Geo-Congress 2020: Geotechnical Earthquake Engineering and Special Topics

A shake table testing program is conducted at the University of California, San Diego, to assess the potential of the polymer injection technique in remediating liquefaction induced foundation settlement. A large laminar soil container placed on a shake table is employed. Emphasis is placed on mitigating the liquefaction-induced settlement of a shallow foundation supported over a large saturated liquefiable stratum. In a series of two shake table tests, the system response is studied first without, and subsequently with polymer injected into the liquefiable stratum. Base excitation is imparted, resulting in liquefaction and excessive foundation settlement in the benchmark experiment. In the second test, after injection of an expansive polymer, a major reduction is observed in the resulting foundation settlement, tendency for pore pressure buildup and associated soil softening. This testing program is a first of its kind and offers insight into the behavior of liquefiable ground remediated by the polymer injection technique.

NorSand is a critical state (plasticity) model for soils in which particle to particle interactions are controlled by contact forces and slips. The state parameter allows capturing soil behavior over a wide range of confining stresses and densities using relatively few and familiar soil properties that can be determined from the routine laboratory or in situ tests. This paper presents the implementation of NorSand in the leading geotechnical software platform FLAC3D. This implemented version includes the usual three-dimensional aspects allowing for the proportion of intermediate principal stress as well as the far less common feature of principal stress rotation; these aspects allow simulation of cyclic mobility as well as static liquefaction. The results are cross-verified with a VBA-coded spreadsheet for simulations of various densities, drainage conditions, and test types, including triaxial compression and simple shear.

Ageing dams located across the west coast of North America, both in the USA and Canada, are threatened by potential for large earthquakes. Assessing the seismic performance of these dams has been a challenge. This paper presents a synthesized approach for assessing the seismic and post-earthquake performance of a dumped rockfill dam built in the 1960s with a gunite (shotcrete) face as the water barrier. The dam may lose its freeboard due to seismic settlements. If loss of freeboard does not occur, the gunite face can still crack and allow leakage. Excessive discharge at the downstream toe due to the through-flow may cause the rockfill at the toe to unravel. Such unraveling and consequent sloughing of the slope may cause a dam breach. The synthesized approach consists of a dynamic analysis and methods for assessing the cracks in the gunite face, leakage through the upstream face, and potential for unraveling and instability of the downstream slope.

Several numerical modeling approaches have been reported in technical literature to determine the seismic soil-structure interaction (SSI) effects in buildings. As part of earthquake-resistant designs of tall buildings, considering SSI effects in the analysis provides more realistic features of its performance during a future seismic event. SSI effects are currently incorporated in building designs using classical impedance functions in the form of translation and rocking springs concentrated or distributed along the foundation level. Numerical simulations using springs and dashpots performed in OpenSees are presented in this paper to simulate the flexibility and the damping of the soil. The results are compared with those obtained using direct approaches considering soil-foundation-structure system in a continuum form. The pressure dependent multi yield (PDMY02) constitutive soil model is used to represent the soil domain underneath archetype tall buildings when subjected to different earthquake time histories. The main goal of this paper is to estimate the difference on the computed seismic response of tall buildings using both SSI modeling approaches. It is concluded that regardless of the SSI modeling approach, the seismic response of tall buildings is affected by the inclusion of SSI effects when compared to conventional fixed-base structure models.

A centrifuge test of a cantilever retaining wall representing prototype wall of 9.14 m height with liquefiable backfill was simulated numerically using simple Finn-Byrne model for liquefaction analysis. Vertical and horizontal motions were introduced to the base of the retaining wall model. Hooke’s elasticity was assumed for the soil behavior. Mohr-Coulomb criterion was assumed as the yield surface. Finn-Byrne formulation was applied for excess porewater pressure generation under dynamic loading. Excess porewater pressures, wall deflections, backfill settlements, and lateral earth pressures behind the wall were computed and compared with the observed measurements. While excess porewater pressures and wall deflections were reasonably predicted, backfill settlements predictions were lower than the measured values. Results were compared with another numerical study that used an advanced constitutive model, i.e., Pastor-Zienkiewicz Mark III, for liquefiable soil. Although Finn-Byrne is much simpler than Pastor-Zienkiewicz model, it can reasonably predict the generated excess porewater pressures and provides very similar settlement estimate as of more advanced models. This study highlights the simplicity and applicability of Finn-Byrne model for liquefaction analysis of cantilevered retaining walls.

In this paper a model is developed to examine the geo-material variabilities and earthquake motions after calibrating the model by carrying out class C numerical simulation based on dynamic centrifuge test on a liquefiable sloping ground using Ottawa F-65 sand. The constitutive model parameters were derived from the result of cyclic torsional shear test carried out at a relative density of 60%. Following the successful validation with the centrifuge test, the constitutive model is used to carry out sensitivity analysis to ascertain the effect of various uncertainties including the material variability present in situ conditions. In order to understand the behavior of a liquefiable sloping ground under realistic scenario earthquake input motions, a numerical study is also performed under 1995 Kobe and 1989 Loma Prieta earthquake motions and the soil system response is compared.

Phononic crystals (PCs) beam has band gaps’ characterization and the potential to inhibit flexural wave vibrations, and it can be used for vibration isolation in beam-foundation systems. To realize the broadband gaps, a multi-frequency locally resonant (LR) PCs model, in which two types of spring-oscillator are periodically attached to an Euler beam, is introduced into the beam-foundation systems. Based on the motion equations of flexural wave in beam, the complex band structures of beam-foundation systems are derived by transfer matrix method (TMM) and Bloch’s theorem. The derivation is verified by the frequency response function (FRF) of the system, which is conducted with finite element method (FEM). Then, the band gap characteristics in the beam-foundation systems are investigated theoretically. Furthermore, the effects of oscillator and foundation parameters on the band gaps are analyzed in detail. Results indicate that multi-band gaps exist in the novel LR PCs beam-foundation system and the multi-frequency LR PCs beam can effectively enlarge the range of flexural band gaps.

This study investigated the dynamic response and liquefaction of saturated-sand level deposits subjected to biaxial shaking using a number of centrifuge tests. Loose sandy soil deposits were built in a 2D laminar container and subjected to a series of biaxial base excitations that approximate in a fairly realistic fashion the conditions of a site subjected to earthquake shaking. A dense array of accelerometers and pore pressure sensors were used to monitor the deposit response. The recorded accelerations and pore pressures were used along with non-parametric identification procedures to estimate the corresponding dynamic shear stress-strain histories. In turn, these histories were employed to assess the effects of non-proportional loading on soil contraction and dilation mechanisms. The predicted response of the soil using the calculated parameters was in good agreement with the recorded one.

Soil liquefaction is relevant to the development of excess pore water pressure and strain, as well as the energy dissipation in the soils. A series of cyclic triaxial undrained tests are conducted on a typical low-plasticity fine-grained soil (Taiping tailings) to evaluate cyclic response at different cyclic stress levels. There are four testing samples subjected to different cyclic stress ratios on the condition of the same void ratio. A unified viscous energy dissipation ratio (VEDR), which is a normalized energy ratio based on the relationship between cyclic stress and strain, is proposed to study the energy dissipation at each cycle. In general, growth trends of cyclic strain amplitude (ε_cyc), excess pore water pressure ratio (r_u), and VEDR for testing samples depend on the applied cyclic stress levels. And the variations of VEDR versus ε_cyc and r_u indicate VEDR is not only related to strain and excess pore water pressure development levels but also can reflect the triggering of excess pore water pressure and threshold strain (close to 0.02%). Additionally, the VEDR results can provide a meaningful basis to study the specific particle behaviors in the process of cyclic loading.

ASCE 7-16 details how the peak ground acceleration (PGA) should be determined for evaluating liquefaction triggering, with this PGA reflecting the influence of a range of earthquake magnitudes on a site’s seismic hazard. Similarly, the Finn and Wightman magnitude-weighting scheme can be used to account for the full range of magnitudes influencing the seismic hazard at a site, where the weights are derived from a site’s seismic hazard deaggregation data. However, the deaggregation data for the seismic hazard maps for the Central/Eastern U.S. are only available for rock motions and not motions at the surface of the soil profile. The authors explore this issue by comparing the weighted average magnitude scaling factors (MSF) and depth-stress weighting factor (r_d) values for multiple sites in the Western U.S. developed using deaggregation data for rock motions and for motions at the surface of the soil profiles. Based on these comparisons, the authors found that using the PGA deaggregation data for rock conditions yield similar weighted averages for MSF and r_d as those computed using deaggregation data for the PGA at the surface of the soil profile.

Analysis of liquefaction and its consequences remains one of the more active areas of research and development in geotechnical engineering. In 1998, a consensus was reached within the technical community on the use of an empirical stress-based approach for liquefaction triggering assessment, called the simplified method. However, regulatory codes and the standard-of-practice recommend performing specific stress-based studies and site response analysis to estimate liquefaction potential. This work presents a comparison between these two approaches to evaluate liquefaction potential. The city of Mayagüez, Puerto Rico, is chosen as the study area because of the high presence of alluvium sand deposits and the complex tectonic setting that surrounds the island. General results indicate that the coastal area of Mayagüez has a high liquefaction potential (factor of safety <1). The simplified-based method showed to be less conservative than the specific-based method. These results can be attributed to the fact that the latter considers soil site effects.

Sloping ground conditions, such as those found in dams and levees, as well as buildings, result in an initial horizontal static shear stress in the ground, affecting its cyclic resistance. When liquefaction triggering is a concern, the K_α correction factor is used to account for this initial static stress in a simplified manner. Laboratory testing was performed to assess the effects of horizontal static shear stress on saturated sands; however, limited data exists for this effect on gravels. In this study, cyclic direct simple shear tests were performed on a uniform gravel to determine the effects of relative density, confining stress, and pore pressure generation on cyclic resistance at increasing values of initial horizontal static shear stress. Tests were conducted using a large-size cyclic direct simple shear (CDSS) device in constant volume conditions on 9mm D₅₀ specimens of a pea gravel (PG9). The effects of relative density on the cyclic resistance of this material were analyzed for loose (47%) and dense (87%) specimens, at three significant vertical effective stresses: 100, 250, and 500 kPa. Testing results show that an increasing horizontal static shear stress has a significant effect on the cyclic resistance and pore pressure generation of both dense and loose uniform gravels, but is more pronounced for loose uniform gravels.

The stratification, behavior, and liquefaction resistance of the shallow deposit of FCR was studied using shake table test and piezocone penetration test (CPTu). The CPTu test was conducted at the end of self-consolidation to assess the FCR profile in terms of strength and homogeneity. The shallow deposit of FCR was then tested under a sinusoidal shaking event to capture its seismic behavior and liquefaction resistance. LVDTs attached to the side of the LSB were used to measure the developed shear strains through depth during the shaking event. The hydraulically deposited FCR was mostly classified as a low-plasticity sensitive clayey silt with high potential for strain softening under cyclic loading using the CPTu results. The flow liquefaction occurred due to the shaking event, as large shear strains up to 10% were developed within the FCR deposit. Large shear strains and heterogeneous medium of the FCR deposit resulted in void redistribution and subsequently increase in pore pressure immediately after the shake.

Several researchers have conducted dynamic shaking experiments to examine the rocking behavior of shallow foundations during earthquake loading. This study analyses the results of 142 of such individual experiments from the U.S., Italy, and Greece conducted on centrifuge and shaking tables. The objectives of this research are (i) to summarize seismic energy dissipation in soil due to rocking, permanent settlement of the foundation, and the self-centering ability of the foundation; and (ii) to explore possible correlations between the above mentioned parameters and rocking coefficient of the soil-foundation-structure system, slenderness ratio of the structure, peak ground acceleration, and the Arias intensity of the earthquake. It is found that energy dissipation and permanent settlement correlate well with the Arias intensity of the earthquake rather than peak ground acceleration. A new parameter, defined as the tipping-over stability ratio, shows that rocking foundations possess excellent stability against tipping over failure.

The objective of this study is to develop a consistent relationship between small strain shear wave velocity (V_s), corrected cone penetration test (CPT) tip resistance (q_c1Ncs), and corrected standard penetration test (SPT) blow count (N_1,60cs) for liquefiable soils. In the absence of actual measurements of V_s in the field, it is common to use data from SPT or CPT testing to estimate V_s. However, empirical correlations between pairs of these in situ metrics can yield significantly different values of V_s. Using recent correlations between cyclic resistance ratio normalized to M7.5 (CRR_M7.5) and V_s normalized to one atmosphere of overburden (V_s1), q_c1Ncs, or N_1,60cs, a consistent relationship is developed such that reasonably similar values of V_s can be obtained using either q_c1Ncs or N_1,60cs. In comparison to two published V_s correlations, the correlations given in this study provide an average V_s value when using N_1,60cs as the dependent variable but a slightly lower prediction of V_s when using q_c1Ncs as the dependent variable.

This paper discusses the data collection, ground motion scaling, development of the model parameters used and the results of a seismic site response analyses at a site where multiple surface wave investigations yielded different bedrock site classes. It is well known that input ground motion selection can greatly influence the predicted response from a site-specific analyses. Another important factor is the depth to bedrock in the soil model. These two factors are interdependent on one another. In fact, the stiffness (shear wave velocity) of the half space where input motions are applied, directly influences the target spectrum (i.e. hazard) used to scale the input ground motions. At a bridge site near Jackson, Wyoming, two different data collection, and hence shear wave velocity profiles have been used to predict surface spectral accelerations using site response analysis. At this site overly-conservative predicted spectral acceleration would have resulted in greater costs if deeper, better quality surface wave data had not been collected. The greater depths of investigation resulted in a stiffer half-space, and hence a more favorable target spectrum. This greatly reduced the predicted design response spectrum at the surface at all periods.

Earthquake excitations often cause an increase in pore water pressure in contractive sands resulting in liquefaction, which can lead to catastrophic consequences. Therefore, it is imperative to assess the earthquake-induced excess pore water pressure and deformations to evaluate the post-earthquake serviceability of the important structures such as earthen dams. The analyses are usually performed using the equivalent linear method or the non-linear method. The purpose of this research is to evaluate and compare the excess pore water pressure and associated deformations predicted using these two methods of analyses. Two numerical models of a typical zoned earthen dam were subjected to two earthquake time-history data with significantly different frequency contents to comprehend the differences in the outcome. The analyses results are similar for dams with dense sand shells when subjected to low-intensity earthquake excitations with the predominant frequency significantly different from the first natural frequency of the structure.

The undrained behaviour of granular materials under cyclic loading is highly influenced by various parameters such as void ratio (e), confining stress (p'), initial static shear stress (q_s), cyclic deviatoric stress (q_cyc), stress reversal (SR), and no-stress reversal (NSR) conditions. Extensive studies have been conducted for evaluating the influence of e, p', q_cyc, and SR on isotropically consolidated specimens. However, a soil element in nature is usually in anisotropically or K₀ consolidated state and hence subjected to a q_s. Literature suggests that the variation of q_s may affect the pore water pressure (Δu) generation, strain (ε_d) accumulation, and fabric (F) even for same e and p'. Current study is a preliminary investigation in evaluating the combined effect of q_s and q_cyc on cyclic liquefaction behaviour of K₀-consolidated soils. Cyclic triaxial simulations were conducted using discrete element method (DEM) on an assemblage of spherical particles. It was found that SR and NSR played a significant role in defining the failure mechanism which is dependent on the magnitude of q_s and q_cyc. In addition to macro study, this study also revealed that micro parameters CN and F_vM can be used for defining the point of initial liquefaction.

Deep wastewater injection-induced seismicity has led to over a thousand M_w>3 earthquakes and four M_w>5 earthquakes in Oklahoma over the last ten years. The 3 September 2016, M_w5.8 Pawnee, Oklahoma, earthquake was the first induced seismic event worldwide, that the authors are aware of, where liquefaction was observed and documented, raising concerns regarding the liquefaction risk posed by future induced earthquakes. Determining the suitability of current variants of the simplified procedure for evaluating the regional liquefaction hazard caused by induced earthquakes is part of an ongoing study. A detailed site characterization campaign examining profiles where liquefaction was and was not observed following the 2016 M_w5.8 Pawnee, Oklahoma, earthquake is part of this study. The purpose of this paper is to present an overview of the sites targeted as part of this testing, a summary of preliminary results from the site characterization campaign, and a description of planned future testing.

The moment magnitude (M_w) 7.1 Anchorage, Alaska, earthquake on November 30, 2018 is one of the largest earthquakes to strike near a major U.S. city since the 1994 Northridge earthquake. No fatalities were reported, but the earthquake caused widespread power outages, structural damage to residential buildings, damage to roadways and railways, and ground failures. This paper presents a summary of preliminary findings by the NSF-sponsored Geotechnical Extreme Events Reconnaissance (GEER) team. Damage was characterized using a combination of on-ground site mapping and aerial reconnaissance with state-of-art geomatics technology and photogrammetry. Recorded peak ground accelerations (PGA) at most stations range between 0.2 g and 0.3 g, with a few sites in the central and southeastern vicinities of Anchorage with PGA greater than 0.5 g. The duration of strong shaking from the M 7.1 event may not have been enough to initiate substantial movements on the majority of the historic landslides from the 1964 M 9.2 earthquake, including the slides at the Turnagain Heights and 4th Avenue. However, liquefaction appeared to have contributed to re-mobilization of the 1964 Potter Hill (Rabbit Creek) landslide. While the majority of the damage observed in Anchorage and surrounding communities appeared to be non-structural, the isolated cases of structural damage seemed to be caused by geotechnical issues, particularly settlement of the foundation and/or slope deformations.

Dynamic soil properties such as shear and compression wave velocities are essential for understanding the dynamic response of soils, which will govern the response of any infrastructure founded on or within the soil mass. Despite this, there are only few studies that systematically evaluate the influence of various basic soil properties on the dynamic soil behavior. In this study, twenty soil samples were prepared in the laboratory as mixtures of the montmorillonite with quartz (rock flour) or kaolinite with quartz to prepare soil samples at a wide range of consistency limits. Liquid limits and plasticity indices of the samples ranged from 8 to 486 and 4 to 431, respectively. The samples were used to conduct bender element tests to determine the shear wave velocities and compression wave velocities at the consolidation pressures of 25 kPa, 50 kPa, and 100 kPa. The impact of mineralogical composition and plasticity characteristics on the dynamic soil properties were evaluated. Consolidation pressure appeared to have a small to negligible influence on the shear and compressive wave velocities of both mixtures of kaolinite with quartz and montmorillonite with quartz. The compression and shear wave velocities of the samples decreased with an increase in the plasticity index of the samples. Greater reductions were observed in mixtures of kaolinite with quartz than in mixtures of montmorillonite with quartz. Unique relationships were developed between the shear and compression wave velocities with the plasticity index. These relationships were found to depend on the mineralogical composition of the sample.

A set of dynamic centrifuge experiments were conducted to evaluate the effect of the depth of the groundwater table on the seismically-induced soil settlement and the maximum lateral deformation of silty sand when the soil was subjected to a suite of scaled earthquake motions. A physical model was designed and was constructed to represent a surface foundation with a width of about 3.5 m. The experiments consist of a test on dry and saturated soil specimens as well as a test on a soil having the groundwater table below the soil surface. The soil specimens were prepared in a laminar container. Results show that the seismic soil settlements in the free field and beneath the foundation as well as the maximum lateral deformations of the soil, having the groundwater table below the soil surface, are smaller than those for the dry and saturated soil specimens.

There have been many cases of flow failure in tailings dams triggered by liquefaction both from static and dynamic lading in the last two decades. In 2016, an aluminum tailings facility failed in China creating an environmental disaster. Currently, there is a lack of research addressing the large strain characteristics of aluminum tailings especially related to its undrained shear strength which is important since the safety of embankments against flow failure is commonly conducted by carrying out post-liquefaction stability analysis. This paper aims to estimate the post-liquefaction shear strength of aluminum tailings by means of undrained triaxial compression tests and the application of steady state theory. Furthermore, to study the effects of plasticity and mineralogy of the aluminum tailings, a mixture of several types of silica sands was prepared aiming to resemble the aluminum’s coarse-fraction gradation. Results showed that quasi steady state response is predominant for aluminum tailings whereas the silica sand mixture shows steady state response at low levels of confining stress and density. Furthermore, a unique normalized undrained ratio for post-seismic stability analysis was obtained and its applicability in engineering design was evaluated.

Site response analysis is an important part of earthquake engineering to evaluate effects of local soil conditions on ground motions for appropriate characterization of the seismic hazard. A reliable prediction of site response for soil deposits is crucial for seismic evaluation of existing geotechnical structures and for design of new structures. This paper presents results of 1-D site response analyses based on work performed for a proposed offshore development in the seismically active Taiwan straits. The deposits in the project area included layered liquefiable deposits which required careful consideration in the site response analyses. The site response analyses were performed using two different open-source tools, DEEPSOIL and Cyclic 1D. The input parameter values for the analyses were modelled after results of a geotechnical investigation and the building code uniform hazard spectrum for the site. Both equivalent linear and non-linear approaches were adopted for the analyses and the suitability and limitations of each approach for liquefiable layers are discussed. The seismic site response results obtained from the two different tools are systematically compared from the standpoint of the peak ground acceleration, acceleration time histories, response spectra, and pore pressure generation. The effect of soil liquefaction on ground motions are also discussed.

New developments are planned at an existing wastewater treatment plant, which provides secondary treatment of the liquid stream for about one million residents and businesses. Existing facilities at the 45-year old plant were designed based on various versions of the building code in effect at the time of construction, and each expansion was designed to a different level of seismic performance. As part of the new expansion phase, additional gravity thickeners are proposed in an area of the site surrounded by several older facilities. The proposed gravity thickeners are designed for post-disaster operation after the design earthquake without adversely affecting the performance of the existing facilities. A suite of 15 spectrally matched ground motions were developed for the 2,475 year design return period, and nonlinear seismic deformation analyses were performed using the finite difference program FLAC and effective stress-based constitutive model UBCSAND. As per conventional local practice, time histories representing the average and upper bound estimates of the Arias intensity and significant duration were identified from the 15 earthquakes during preliminary design, and seismic-induced displacements of the facilities were evaluated. Subsequently, the performance of the structures was assessed under all 15 time histories. The analyses showed that the initial selection of time histories based on the average and upper bound Arias intensity and significant duration did not correspond to the average and upper bound displacements under all 15 time histories. It is evident that conventional selection of earthquake records may not result in the examination of the most critical displacement cases.

This paper implements an identification technique to characterize the pore pressure behavior of a fully instrumented wildlife site located in the Imperial Valley of Southern California. A 12-year seismic history of the site was analyzed. The technique estimates shear stresses and strains based on acceleration and pore pressure recorded using a vertical array of sensors in the deposit. A constitutive model was implemented to identify optimal material parameters controlling the contractive behavior of the soil based on the recorded response of all seismic events. The relationship between the maximum acceleration and pore pressure ratio was analyzed, as well as the relationship between the maximum acceleration and a parameter controlling the contraction of the soil. It was found that the seismic history of the deposits affects the contractive tendency of the material, which significantly influences the pore pressure response of the deposit.

Simplifying the assumptions of a problem may lead to significant design and analysis cost reduction, but increase the risk of hazardous consequences, especially when safety-critical structures such as large dams, skyscrapers, etc. are involved. These simplifying assumptions usually come from considering a homogeneous foundation, while inhomogeneity in rock foundations is more rational in modeling of these mega structures. On the other hand, considering a unique geometry of inhomogeneity and mechanical properties for all site foundations around the world is impossible. The purpose of this study is to perform probabilistic analysis of a critical geometrical situation for concrete gravity dam-reservoir-foundation system, using two approaches of Latin hypercube sampling (LHS) and first-order second-moment (FOSM). Pine Flat Dam is considered as a reference case and tensile strength, sliding of dam base and opening of dam heel are considered as controlling performance functions. The results illustrate that exceedance probability (EP) curves which are resulted from FOSM method are not reliable, whereas the shape of curves are similar to the curves resulted from LHS approach. Furthermore, the results show that the importance measure vector can be derived from FOSM method, while the LHS approach is incapable of providing this information.

The great potential of economic benefits of utilizing underground spaces in the urban areas around the world has made the use of underground infrastructures popular. This makes the researchers to perform comprehensive studies of the effects of deep excavations on nearby properties. The protection of adjacent and underground facilities and lifelines during an earthquake is one of the major challenges in design and construction of ground excavations and foundation engineering. Excavation-induced ground movements could be greatly intensified during an earthquake. Large ground deformations may result in cracks or sever damage in adjacent lifelines. Therefore, to reduce the risk of lifeline failures, the seismic response of lifelines adjacent to deep excavations should be completely studied. In the present study, the dynamic performance of a buried pipeline close to a deep excavation is investigated using ABAQUS software. A series of three-dimensional (3D) finite element (FE) analyses are conducted and the normalized tensile strain are plotted to analyze dynamic response of the buried pipe.

Seismic soil-structure interaction (SSI) has the potential to significantly influence seismically-induced ground failure; however, despite recent advances, the contribution remains poorly understood and is routinely neglected in geotechnical engineering practice. Observations from the 1999 Kocaeli, Turkey, and 1999 Chi-Chi, Taiwan, earthquakes indicates SSI effects may be pronounced in the cyclic softening-induced ground failure of low-plasticity, fine-grained foundation soils. The authors recently completed a centrifuge modeling program that seeks to address this knowledge gap by evaluating the SSI-based seismic demand imparted by shallow foundations on fine-grained soils and the corresponding contribution to cyclic softening-induced ground failure. This paper presents preliminary results from the modeling program, including observed peak ground acceleration (PGA), peak structural acceleration, and structure settlement. The influence of SSI effects is demonstrated by comparing observed structural settlement to structure factor of safety evaluated using dynamic bearing capacity calculations.

Many complex soil-structure interaction problems can be simplified by considering one-dimensional beam (structure) resting on elastic spring (soil). The present study uses Winkler formulation to investigate the effect of transverse permanent ground deformation (PGD) on buried continuous pipeline. Starting with a brief review on previous studies in the area of PGD, present study developed a closed-form formulation for the pipe under transverse PGD based on available boundary conditions and compatibility conditions and then the current analytical analysis is validated with the pipe deformation curves along the PGD zone obtained by earlier researchers and it has been found that validation curves are matched in good agreement. Further, the proposed closed-form solutions are used to obtain the influence of various parameters such as PGD width, peak ground deformation, soil stiffness on pipe response.

This paper presents a novel procedure, discretization-based kinematic analysis, to investigate the seismic slope stability at limit state. Such a procedure combines the merits of highly efficient kinematic analysis with adaptive discretization technique for generation of kinematically-admissible failure mechanism for non-uniform soil slopes with varying soil strength parameters, which cannot be readily solved using conventional limit analysis. The proposed approach is applied to a non-uniform soil slope to demonstrate the adaptability of the procedure for wider applications. The upper bound formulations of yield seismic acceleration and/or limit surcharge are derived based on the balance of work rate. Through an optimization procedure, the least upper bound solutions are sought under given parameters, and the critical failure mechanism can be characterized simultaneously.

This paper introduces a series of centrifuge tests—under low and high confining pressures—designed to study the effect of effective overburden pressure on liquefaction potential of clean sand. All the centrifuge tests simulate about 5 m saturated clean sand deposit under effective overburden pressure of 1 and 6 atm with relative density ranging from 45% to 80%. To achieve the targeted overburden pressures, a dry layer of lead shots with different thickness was deposited on top of the clean sand. Viscous fluid was used for saturation to keep constant prototype permeability. All the centrifuge tests were subjected to 10-cycle sinusoidal seismic motions with different prototype peak acceleration to achieve the targeted maximum excess pore pressure buildup. Acceleration, pore pressure build-up and dissipation, and shear wave velocity were monitored, recorded, and analyzed during or after shaking. Acceleration amplification was observed in experiments conducted under low confining pressures, while de-amplification was found in experiments conducted under high confining pressures.

One of the first steps in assessment of liquefaction hazards consists of evaluating the potential for liquefaction triggering at a site. Procedures based on the standard penetration test (SPT) and cone penetration test (CPT) are often used. However, geophysical measurements of shear wave velocity (V_S) have also been used to evaluate liquefaction triggering since V_S is a proxy for soil stiffness. Measurements of V_S for these triggering evaluations are often acquired using downhole methods (e.g., seismic CPT or P-S suspension logging) or cross-hole methods. SPT, CPT, and borehole-based geophysical measurements provide data in the localized region surrounding the boreholes. This presents challenges when attempting to evaluate liquefaction triggering in natural soils that exhibit spatial stiffness variability. Recently, surface wave measurements have grown in popularity for geotechnical investigations and have been used to evaluate V_S profiles for liquefaction triggering analysis. However, surface wave methods typically apply wavefield transformations to evaluate dispersion characteristics. This essentially introduces a form of spatial averaging that can lead to uncertainty in V_S measurements when soils exhibit appreciable spatial variability along the survey line. One promising development in surface wave testing involves the use of full waveform inversion (FWI). FWI attempts to match the entirety of each recorded signal rather than a dispersion curve derived from the corresponding wavefield transformation. Therefore, FWI has the potential to offer broad spatial coverage while avoiding the inherent limitations of a dispersion-based surface wave approach. In this study, numerical modeling was performed to simulate wave propagation in soils exhibiting natural spatial variability. Comparisons were made regarding the extent to which different geophysical approaches could reliably estimate liquefaction triggering. The results demonstrated that FWI can outperform downhole/cross-hole measurements and a dispersion-based surface wave approach when implementing V_S-based liquefaction triggering procedures in spatially variable soil conditions.

In this study, a three-dimensional analysis of soil-retaining wall dynamic interaction is conducted using the discrete element method (DEM). In this method, soil grains are treated as rigid spherical particles which are allowed to overlap one another at contact points. The forces and motions inside the assembly are calculated utilizing Newton’s second law of motion together with force-displacement laws. The deformable sheetpile-type retaining wall is simulated using rigid balls glued together by parallel bonds with specific strength and stiffness to mimic the physical properties of the real wall. Due to computational limitations, the high g-level concept and scaling laws for dynamic centrifuge testing are employed to decrease the domain size and simulation time. In addition, absorbing boundaries are employed at lateral sides of the model to prevent the reflections of the propagating waves back to the assembly. Seismic excitation is introduced to the system through the base wall, which represents the bedrock. The effects of different characteristics of the input seismic wave such as its frequency on the dynamic response of soil-sheet pile system are analyzed. Furthermore, data on lateral thrust and bending moment on the wall as well as its deflection is collected. It is shown that the numerical method is a competent tool to evaluate and predict the dynamic response of soil-sheet pile systems.

In this study, a three-dimensional microscale framework utilizing the discrete element method (DEM) is used to examine the seismic response of dry granular slopes under different conditions of ground motions. The presented model inherently accounts for soil nonlinearity and damping in response to shear deformations. The essential characteristics of wave propagation including motion amplification and resonance were observed from the computational results. The impact of amplitude and frequency of input motion on the response of the slope was examined. Shaking-induced softening of the soil composing the slope may shift its natural frequency to values very close to the frequency of the dynamic motion, leading to a near-resonance condition in which the slope experiences severe deformation.

Estimating the amount of liquefaction-induced building settlement during liquefaction phenomenon due to soil ejecta is a challenge not resolved yet. Current state-of-the-art recommends using engineering judgement and comparison to exemplary case histories, but no studies have been conducted yet that collect and summarize the existing case history data on liquefaction-induced soil ejecta. This study collected observations from the geotechnical extreme event reconnaissance (GEER) database, selected publications on liquefaction, and photographic evidence of ejecta near buildings and organized the information regarding earthquake, soil, and building properties as well as building movements, ejecta properties, and occurrence. The processed data of 20 major earthquakes was categorized and presented in several plots to identify possible general rules of ejecta occurrence and building movement. Frequency and distribution of ejecta properties and occurrence as well as magnitude and intensity measurement of the earthquakes with ejecta incidents were assessed and the influence of distance between ejecta and buildings studied. This paper explains the processing of the collected case history data and summarizes the results of the empirical analysis that identifies future directions for the assessment of ejecta-induced building movement.

Due to the complexity of wave propagation in soil media and the uncertainty in geotechnical material properties, predicted surface motions using theoretical wave propagation models often deviate from recorded surface ground motions. This gap highlights the need for more representative seismic wave propagation models. Seismic wave propagation based upon Kjartansson's constant-Q concept is one such model, in which the energy loss during each cycle is considered to be independent of frequency. A fundamental feature of the constant-Q model is that the soil stress-strain relationship involves time derivatives of fractional order (called the FD model here). The complete identification of the FD model requires determining three parameters, including the soil density, shear wave velocity at a reference frequency, and dissipation factor. This study performs a probabilistic calibration based on Bayes’ theorem to arrive at most likely estimates of the parameters of the FD model. In the calibration process, we develop theoretical transfer functions by solving the Kjartansson's constant-Q model in the frequency domain. The theoretical and empirical surface-downhole transfer functions are computed for a Kiban-Kyoshin network (KiK-net) site and subsequently used in the likelihood function of Bayesian calibration approach. In this investigation, we present posterior probabilistic models for the parameters of the FD model, which facilitate probabilistic linear and equivalent linear site response analysis for cases where the FD model is used to define soil behavior. Moreover, results of this study show that the constant-Q model offers an accurate representation of seismic wave propagation in soil media.

Recent studies have focused on how the dynamic response of a clean sand changes with increasing fines content; however, there remains a limited understanding regarding the effects of increasing coarse content. This study aims to elucidate these effects at a system level via centrifuge testing of two uniformly-graded and one well-graded soil mixture which range in mean grain diameter (D₅₀) from 0.18 to 2.58 mm and in coefficient of uniformity (C_U) from 1.53 to 7.44. Models of each soil mixture were prepared to approximately 50% relative density (D_R) and subjected to uniform cycles of sinusoidal acceleration at various Arias intensities (I_a). The high hydraulic conductivity (k) of the coarsest, uniformly-graded mixture prevented significant excess pore pressure generation; however, liquefaction was induced in the other two mixtures. Furthermore, the well-graded mixture exhibited a stronger dilative tendency than the clean sand. The centrifuge results were compared to cyclic direct simple shear (DSS) results in order to consider the complementary perspectives that centrifuge and element testing can provide.

Fabric and boundary conditions determine the hydro-mechanical behavior of rock masses. In this numerical study, a set of two-dimensional models are created to simulate various layered rock fabrics. The fabric varies in terms of density and relative orientation of natural fractures. The behavior of differently-structured blocky media is analyzed due to a mechanical disturbance that resembles the creation of an opening-mode discontinuity in the medium analogous to hydraulic stimulation. The response of the blocky medium is also investigated in terms of the amplitude of this idealized stimulation resembling the viscosity or flow rate of the injected fluid. The analysis is performed using the distinct element formulation, which can capture the opening and shear failure of existing discontinuities and deformations of the rock blocks globally-disturbed under high far-field stresses. The results show fundamental differences in the deformation field of rock masses with different fabrics. Local shear dilation along natural fractures and global kinematic dilation of the stimulated reservoir area are dominant mechanisms although both processes are more limited than the case of rigid block assemblies under low stresses. The amplitude of kinematic dilation differs for different fabrics, and it implies the extent of enhancement in the permeability of the rock mass.

The existence of uncertainty in the design parameters of anchored rock slopes warrants reliability based study. An approach for reliability based design optimization of anchored rock slopes against plane failure is described under different hydraulic distributions. Planar slide failure along with water pressure has been considered in conjunction with Barton-Bandis failure criterion to compute the factor of safety. Nonlinear strength criterion is employed for the computation of strength of jointed rock mass. The rock bolt and rock mass interaction model is used to analyze the stabilizing force in anchors. The variability associated with Barton-Bandis parameters, namely joint compressive strength (JCS), joint roughness coefficient (JRC), and basic friction angle (ψ) and a joint factor is considered. The target reliability based design optimization (TRBDO) is used to obtain an optimum length of the rock bolt and optimum anchor force required to stabilize the rock slope in order that the reliability index must meet a desired level of safety.

The performance and maintenance of infrastructure assets passing through rock cuts depend on the stability of the rock slopes. Most of the previous slope stability works used simplistic two-dimensional slope analysis due to the limitations in analysis software and data collection methods. Three-dimensional understanding of the slope behavior is necessary to estimate the factor of safety of slopes with complex geometry. Three-dimensional analysis conducted in this research is based on method of columns which is an extension of method of slices considered for most two-dimensional analyses. This analysis requires comprehensive data collection of slope geometry, but the present traditional methods are limited by their inaccessibility to hard-to-reach areas on the steep rock slopes. The advancement in lightweight compact sensors complimenting the robust unmanned aerial platforms have found their applications in remotely conducting quantitative assessments of infrastructure assets. The research presented in this study discusses the usage of aerial photogrammetry in collecting rock slope data and three-dimensional stability analysis using commercially available software in which the generalized Hoek-Brown (HK) failure criterion is used to represent the true failure envelope of rock mass. Morgenstern-Price stability analysis method was used to evaluate the global minimum factor of safety. This approach has resulted in significant savings in data collection time and cost, but also provided comprehensive idea about the stability of rock slopes for a given set of material properties.

Understanding of crack initiation and propagation in intact rocks is extremely important in rock engineering. The purpose of this study is to identify the different stages of cracking in intact prismatic rock specimens using the acoustic emission (AE) monitoring technique. The testing program involved uniaxial compression testing of Barre granite specimens with eight AE sensors epoxied on the planar surface as well as sides of the specimen. During the experiments, crack induced due to the uniaxial loading was monitored by AE parameters. The rate and the cumulative plots of the AE hit and energy reflected the various stages of crack initiation and coalescence. The study focused on the determination of crack initiation and crack damage stress thresholds using cumulative AE hit method (CAEH) and cumulative AE energy method (CAEE), respectively, and both methods allowed the identification of several cracking stages, including the crack closure, elastic deformation, crack initiation, microcrack growth (stable growth), crack damage, and unstable crack growth.

Small-strain dynamic properties of 23 rock cores, collected from two dam spillways and adjacent exposed rock areas, were tested using the unconfined, free-free, resonant column (URC) method. The URC method, introduced in 1994, is a nondestructive, dynamic method to independently determine shear, unconstrained-compression, and constrained-compression wave velocities (V_S, V_C, and V_P, respectively). These wave velocities have many uses such as: (1) identifying stiffer versus softer zones, (2) permitting direct calculation of three values of Poisson’s ratio with which each rock core can be characterized as isotropic or anisotropic for use in evaluating core quality and developing robust correlations, and (3) with mass density, calculating small-strain moduli for use in numerical modeling. The laboratory data determined with isotropic cores show clear correlations between: (1) wave velocities and Poisson’s ratio, (2) unconfined compressive strength and mass density, and (3) field and laboratory V_S values. No clear correlations were found with anisotropic cores.

The paving fabric, a stress-relieving interlayer, was used in this study to reduce reflective cracking. The mechanisms of reduction of reflective cracking through paving fabrics are stress relief and waterproofing. The nonwoven geotextiles are selected as paving fabrics in this experiment. The objective of this study was to evaluate the effectiveness and performance of paving fabric on reduction of reflective cracking in the field. The twelve 150 m pavement sections of a four-lane highway were rehabilitated, and then monitored for seven years in the state of Mississippi. Another factor such as overlay thickness on long-term performance with paving fabric was also studied. The results indicated that the paving fabrics and thicker overlay thickness can significantly reduce the reflective cracks and delayed the cracks growth.

In this study, falling weight deflectometer (FWD) tests were performed on 12 asphalt pavement sections in South Carolina to estimate the resilient modulus (M_R) of the subgrade soil using three back-calculation tools: BAKFAA, SCDOT Program, and AASHTOWare. Repeated load triaxial tests were performed on soil samples obtained from the pavement sections to obtain a direct measure of M_R. The data obtained from these methods were used to study the feasibility of using the subgrade M_R found from the FWD test to subdivide pavement sections (ranging in length from 2 to 40 km) into multiple, shorter pavement sections for use in the local calibration of the MEPDG. In South Carolina, the number of pavement sections with data available for local calibration is limited, thus subdividing the pavement sections based on changes in material properties will help increase the number of pavement sections for local calibration. Results show that the M_R values found from the FWD data have similar trends to the laboratory measured M_R values. Based on findings from the FWD testing, 4 of the sections exhibited 2 different M_R profiles, 1 section exhibited 3 different M_R profiles, and 7 sections had relatively constant M_R profiles along the length of the sections. Thus, 6 additional sections have been identified. Work is ongoing to analyze additional data to identify additional pavement sections.

Pavement deterioration due to frost action is a challenge for transportation infrastructure in the northern part of United States. Combination of the variation of subgrade temperature, moisture, and soil type leads from minor to severe frost damage. Accumulated water causes the differential frost heave during freezing temperature followed by settlement in subsequent thawing days in seasonally frozen areas. While the classical solution suggests using granular materials up to freezing depth which comes with substantial cost, insulation can be an effective alternative to prevent the frost action reaching the frost susceptible soil. With an attempt to moisture and temperature adjustment, geocomposite insulation layer was modeled in numerical environment. Geosynthetics layers consisting a geonet sandwiched between geotextiles at top and bottom was placed before the subgrade. The top and bottom geotextile layers acted to prevent both downward and upward moisture flow in the pavement. The numerical modeling results yielded to less moisture variation following precipitation. In addition, it was also found that the maximum freezing depth was reduced after using the geosynthetics layer. As such, the study suggests insulation using geosynthetics layer can be an effective solution for reducing frost damage risk in frost susceptible areas.

This paper provides information on the plastic mold compaction device (PM Device) developed and evaluated over the past few years to improve paving with chemically stabilized soils. The PM device can produce test specimens with a height/diameter ratio of 2:1 in the laboratory or the field. Recently, AASHTO PP 92-18 was approved, which is a national method for use of the PM device, and this paper builds upon this method and outlines some implementation-oriented procedural considerations not specifically addressed in PP 92-18. Of primary interest herein was improved quality through variability reduction that is believed to be possible by way of the PM device. Environmental ramifications of reduced variability were shown to be substantial in the context of cement usage reduction and that additional mixing energy needed to achieve uniformity was far outweighed by even modest cement usage reductions. Potential economic advantages of the PM device would be associated with increased pavement life from more uniform construction.

Loss of coarse aggregate is a common problem for granular roadways due to a lack of fine particles with binding capability. Chemical stabilization is one of the most commonly applied techniques to solve the binding issue of coarse aggregates in granular roadways. However, such methods are usually not economical and may pose environmental concerns such as leaching of heavy metals and nitrates. Quarry fines are the by-product of the crushing process of stones during aggregate production. They can be used as alternative materials to overcome the binding problem while ensuring the treatment is sustainable, economical, and environmentally friendly. The binding capacity of a soil material is directly related to its plasticity index (PI), alumina content, and fineness. In the current study, quarry fines from seven different sources were collected and assessed for their capacity to bind granular aggregates. X-ray fluorescence (XRF), sieve-hydrometer tests, and Atterberg limit tests were conducted on each quarry fines material. Binding capacity of the materials were assessed via vane shear and pocket penetrometer tests on quarry fines specimens prepared as a slurry. In addition, the optimum mixtures of quarry fines with surface aggregates were investigated by comparing the results of California bearing ratio (CBR) tests, for which pairwise correlations were found. Overall, the results show that quarry fines with higher alumina content and PI had higher binding characteristics.

AASHTOWare pavement mechanistic empirical (ME) analysis software was used by the design team to optimize the PCC pavement and foundation system on the I-25 North Express Lanes Project (Johnstown to Fort Collins, CO). The pavement foundation system was designed and resilient modulus (M_r) target values assigned for subgrade, subbase, and a geogrid stabilized aggregate base layer. To verify that the design M_r values were achieved during construction, automated plate loading testing (APLT) was used at point locations as part of the quality assurance (QA) program. In addition, validated intelligent compaction (VIC) testing was implemented on a portion of the project to collect geospatial maps covering 100% of the work area to help the contractor improve compaction process control to achieve maximum uniformity as a quality control (QC) measure. This paper describes the application of APLT and VIC technology to establish the field target values based on the ME design input values accounting for stress-dependency. The paper also describes the process and results for statistically calibrating the VIC output to stress-dependent resilient modulus (R²>0.9) for the pavement foundation layers and engineering interpretation of the results. The innovative methods used in this project demonstrates how assumed ME pavement design values can be used in field process control and verification testing. By improving field verification of the design input parameters, the QC/QA process is optimized, and greater assurance is provided that long-term pavement performance will be achieved.

The placement of soil at a prescribed lift thickness during earthwork construction plays a critical role for ensuring the effectiveness of subsequent soil compaction. A majority of earthwork construction specifications consequently mandate that soils be placed and spread to a “not to exceed” target lift thickness. This approach is common for both “method-based” and “end-product-based” specification frameworks for soil compaction. To date, little research has been performed to assess the viability and relative accuracy of emerging tools that can be used to monitor soil lift thickness, either prior to or post-compaction. In the current study, two innovative pieces of survey equipment were examined: the MIT SCAN T3 nondestructive thickness scanner and a compaction roller mounted with a continuous compaction control (CCC) kit with real-time kinematic global positioning system (RTK-GPS) measurement capabilities. A compacted soil test pad was constructed, which had 82 pre-determined locations that were surveyed to measure the post-compaction lift thickness for a given compacted soil layer. Lift thickness measurements made by the MIT SCAN T3 and RTK-GPS measurements from the compaction roller were compared against physical lift thickness measurements made utilizing a caliper and steel ruler. Lift thickness measurements along the embankment ranged from 10 cm to 70 cm, with the MIT SCAN T3 measurements having an average absolute error of less than 0.5 cm, and the RTK-GPS measurements made from the compaction roller having an average absolute error of less than 2.0 cm. The results from this study illustrate the relative accuracy that can be achieved for these two approaches for assessing compacted soil lift thickness.

Flexible pavements constructed over expansive soil suffer from longitudinal cracking, rutting, surface depressions, and shoulder dropping problems. Rehabilitation of these roads can be done by replacing the existing base layer with recycled asphalt pavement (RAP) material. However, the use of 100% RAP in the base layer is not feasible due to its excessive lateral movements and permanent deformations. Geocell can be used as reinforcement for the base layer constructed with RAP which helps to address these problems. In this study, a test section was constructed with 10 cm thick high-density polyethylene (HDPE) geocell and filled with RAP material. The performance of the test section has been monitored from the load and deformation sensors, topographic survey, and visual inspection methods. Initial results obtained from the field sensors indicate that the utilization of geocell in the base layer reduces the stresses on the subgrade layer and only negligible deformations were measured under the base layer.

In the current study, a mechanistic-based analysis was conducted to compare the mechanical performance of granular roadway test sections built with three aggregate options. Each test section was tested using light weight deflectometer (LWD), international roughness index (IRI), dustometer, and gradation tests to determine the stiffness, surface roughness, dust production, and fines content, respectively. In addition, the abrasion resistance was measured by Los Angeles (LA) abrasion, micro-deval, and C-freeze tests for each aggregate material and results were correlated with field data. Abrasion and freeze/thaw tests indicated the durability of aggregates were greatest for Lime Creek formation Class A (LCF CA), followed by Oneota formation dolomite Class A (OFD CA), with Bethany Falls limestone Class A (BFL CA) having the lowest durability. LCF CA had the best performance with respect to stiffness, roughness, and dust production, and also had the lowest fines content along with OFD CA. However, OFD CA had the largest dust production and roughness values, while BFL CA had the lowest stiffness and maximum fines content. In addition, good correlations were observed between the results of C-Freeze tests and stiffness and fines contents.

Reflective cracking is one of the most common types of distresses that occur in composite pavement system. This study conducted extensive one-at-a-time (OAT) sensitivity analyses to determine the effects of traffic levels, structural design inputs, and material properties on AASHTOWare pavement mechanistic-empirical design (PMED) long-term (20 years) reflective cracking performance predictions for Iowa asphalt concrete (AC) over jointed plain concrete pavements (JPCP). The results showed that the most sensitive input to long-term (20 years) PMED reflective cracking predictions was joint spacing. The moderately sensitive inputs included JPCP layer thickness, AC thickness, tensile strength at -10 °C (14 °F), transfer joint load transfer equivalent (LTE), and the ratio of slabs distressed before and after restoration. The rest of the inputs investigated had either negligible or no impact on long-term (20 years) PMED reflective cracking predictions.

This paper focuses on a laboratory study directed towards quantifying local stiffening of mechanically stabilized geogrid-aggregate specimens through shear wave velocity measurements using bender element shear wave transducer pairs and, at the same time, measuring permanent strain accumulations in repeated load triaxial testing. Crushed stone aggregate base material samples were prepared at three different gradations conforming to the upper bound, mid-range, and lower bound gradations of the Illinois Department of Transportation’s CA06 dense-graded aggregates. All specimens were compacted at the target maximum dry unit weights and optimum moisture contents. Geogrid-aggregate specimens were stabilized with geogrids of two different triangular aperture sizes placed at mid-specimen height. In addition, unbound aggregate control specimens were prepared and tested for comparison. Three pairs of bender elements were installed above mid-specimen height for all the specimens tested with and without geogrids. Repeated load triaxial testing was conducted following AASHTO T307 standard test procedure for resilient modulus. Shear wave velocities and permanent deformation accumulations were measured at the conditioning stage and at each of the 15 applied stress states. The trends of permanent deformation accumulation in test specimens reveal that the engineered mid-range gradation specimen stabilized with the smaller aperture geogrid had the least permanent deformation accumulated when compared to other aggregate gradation and geogrid combinations. This was also in agreement with the largest shear wave velocities measured in the vicinity of the geogrid thus indicating that better geogrid-aggregate interlock is observed for densely packed engineered mid-range gradation specimens stabilized with the smaller aperture geogrid.

For years, geosynthetics have been placed at the interface between the granular base course and the weak subgrade of pavement sections to provide stabilization. Geosynthetics may provide physical stabilization (i.e., separation), mechanical stabilization (lateral restraint), and reinforcement (tensioned membrane effect). For pavement design, allowable deformation is typically limited to 13 mm or less, so only separation and lateral restraint are mobilized in the pavement section. Although geosynthetics provide marked improvements in soil stabilization and pavement performance, a single approach to account for these improvements by separation and lateral restraint has not been well established. Various geosynthetics allow for different design considerations in varying climatic and load-intensity situations. This study focuses on geogrids but uses non-stabilized sections as control sections. Products were selected from a state department of transportation pre-approved materials list in order to remove bias in selection and to mimic the potential selection process in practice. Geosynthetics were installed at the interface of 250 mm of vibratory-compacted granular base course and weak subgrade in large-scale box tests. Cyclic loading was applied at eleven load intensities or until 25 mm maximum deformation was achieved. Permanent displacement at the surface of the base course and interface pressure beneath the geosynthetic (at the top of the subgrade) were recorded. Stress distribution angle and stress patterns at the bottom of the base course were observed. This paper discusses the effects of geogrid as a means of stabilization in terms of interface stress reduction as well as the ratio of permanent to resilient deformation. In this study, replacement of virgin aggregate with recycled concrete aggregate reduced the interface stress by 55%; addition of geogrid to both sections further reduced measured interface stresses. Addition of geogrid effected greater permanent deformation but a smaller incremental deformation in both VGB and RCA. The implications for pavement performance are also discussed.

Particle transport in porous media can significantly compromise the serviceability of civil infrastructure. For example, pumping or migration of saturated subgrade soil to pavement subbase, adversely affects the performance of the pavement and leads to its failure. In this study, an analytical framework is implemented to 1) understand mechanisms of pumping, and 2) estimate the amount of subgrade fines migration into subbase under traffic loads. The model is verified using results obtained from experimental investigations previously conducted to quantify the amount of pumping. The experimental tests were conducted using one-third model mobile load simulator (MMLS3), an accelerated pavement testing (APT) device. Results showed that the analytical model provided a reasonable prediction of the amount of fines migration from a saturated pavement subgrade to subbase. The study also revealed that the subgrade pumping and the deposition process is governed by hydraulic condition, erodibility of subgrade, grain size of subgrade, grain size and pore size of subbase, permeability of subbase, and viscosity of pore fluid in the subbase.

The primary objective of this paper was to measure elastic modulus to compressive strength improvements within in-placed recycled materials that incorporated steel slag. Laboratory mixtures containing cement, steel slag, and in-place recycled pavement were evaluated. Test specimens were prepared with an emerging tool referred to as the PM device. Raw materials were taken from an in-place recycling project in Mississippi and blended with varying cement and steel slag dosages. Use of 15 to 30% steel slag allowed removal of 1% cement while improving elastic modulus roughly 15 to 20%. Higher modulus at lower cement dosages, all other factors remaining constant, reduces plastic shrinkage cracking while also reducing pavement deflections, both of which increase pavement life. Additional, but manageable, compactive effort should be expected for mixtures containing steel slag. Pavement designers are encouraged to consider non-expansive steel slag for in-place recycling projects where the existing material is mostly reclaimed asphalt pavement.

The 2017 reconstruction of MnROAD-National Road Research Alliance (NRRA) low volume and mainline road test sections involved constructing a range of pavement surfaces and foundations. This paper presents results from automated plate load testing (APLT) and validated intelligent compaction (VIC), which was used to develop spatial coverage maps of resilient modulus on finished unbound foundation layers. Testing was performed in selected test sections of the low volume road test track, with the primary objective of measuring in situ resilient modulus (M_r) of the unbound pavement foundation layers. The surface at the time of testing ranged between relatively soft clay subgrade to well-compacted and relatively stable aggregate base layers. The aggregate subbase/base layers in some of the test sections included large stone subbase, conventional aggregates, and recycled concrete aggregates. VIC field calibration testing was performed with APLT to determine cyclic stress-dependent composite M_r as well as backcalculated M_r values for the overlying granular base/subbase and the underlying subgrade. VIC mapping on some test sections showed increasing M_r with increasing pass, demonstrating the need for additional compaction effort that would have not been realized without real-time mapping. VIC mapping also demonstrated significant variability in M_r properties between the test sections and within each test section.

The main goal of this study was to assess accelerated methodologies for determination of base SLCs in Florida base materials. It is desired that the traditional empirical and observationally based technique for determining layer coefficients be streamlined by either an accelerated loading process or by the computer simulation of pavement performance. The paper describes an accelerated methodology that uses the idea of Timm et al. (2014) in which the structural numbers (SN) of two paired test sections are used to backcalculate the unknown SLC. The SNs are determined from the AASHTO performance equation using a prediction of pavement performance from the University of Florida (UF) top-down cracking (TDC) model. The paper presents positive application of the methodology for two test sections in Louisiana and two sections in Florida.

The price of virgin aggregates has increased due to the high demand, lack of high-quality aggregate sources, and federal/local restrictions about their production. In this study, the use of recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP) materials in pavement foundation systems were evaluated as the two alternatives to virgin aggregates. Four full-scale base layers were constructed with coarse RCA, fine RCA, limestone (control), and RCA+RAP materials. Falling weight deflectometer (FWD) and laboratory resilient modulus (M_R) tests were performed to evaluate the field and laboratory stiffness of the base layers and the materials, respectively. Test results exhibited that the recycled materials were good alternatives to virgin aggregates and the trend of laboratory M_R test results were somewhat similar to FWD test results. Coarse RCA and fine RCA resulted in higher M_R and elastic modulus than those of limestone and RAC+RAP.

Granular roads are important to the economies of rural communities, as they provide access to urban areas and comprise one of the main transportation systems for hauling agricultural products. However, such roads may be subjected to heavy traffic loads from agricultural machinery and animal husbandry equipment, and suffer severe damage from seasonal freeze-thaw cycles which cause various types of deterioration including material loss, potholes, frost boils, rutting, and loss of crown. Reconstruction and maintenance of these roads can be costly depending on the frequency and severity of their damage. To improve the performance and reduce the frequency of maintenance and repair of granular roadways, various chemical and mechanical stabilization methods may be used. In the present study, test sections were constructed in four counties around Iowa as part of an ongoing research project to study the performance of five chemical and eight mechanical stabilization methods. In this paper, the performance is evaluated and compared for selected test sections in three of the counties stabilized using the following four methods: (1) a novel optimized gradation with clay slurry method, (2) ground tire rubber incorporated into the surface course, (3) Portland cement incorporated into the surface course, and (4) a proprietary chemical stabilizer mixed with the subgrade and surface course. To evaluate the performance of the test and control sections, light weight deflectometer (LWD) and dynamic cone penetrometer (DCP) tests were conducted to determine the elastic modulus and shear strength of the granular surface and subgrade layers. Based on the test results, the novel optimized gradation with clay slurry and cement-stabilized sections provided the greatest improvements in performance.

Compaction is one of the most important operations in pavement construction. Poor compaction of base and sub-base can lead to various types of deterioration/failure, and consequently increase the cost of maintenance and rehabilitation. Non-uniformity and inconsistency of the compaction are the most prevalent problems associated with conventional compaction techniques. The density-based quality control (QC) and quality assurance (QA) practices for compaction evaluation (spot test measurements) only cover less than 1% of the compacted area. Therefore, there is a need for transitioning from a point-wise to system-wide inspection practices. Intelligent compaction (IC) is an innovative technology that can improve the uniformity and consistency of compaction and provide a system-wide stiffness-based inspection practice. The main objective of this study was to evaluate correlations between intelligent compaction measurement values and in situ spot test measurements. To this end, spot measurements were taken during IC operation in a reclaimed base project in Route 117, Vermont, and simple linear regression models were built to investigate the correlation between intelligent compaction measurement values (CMVs) and dynamic cone penetration index (DCPI)/nuclear gauge density (NGD)/pavement quality indicator (PQI)/core densities. The results indicated that the correlation between the CMVs and spot measurements was meaningful only in case of DCP tests performed during the initial reclaim phase. Different mechanisms for compaction quality measurement and variation of material properties throughout the project were the main reasons for the observed weak correlation.

The objective of this study was to capture the changes in mechanical properties of the base course when materials are compacted at maximum dry density (MDD) and optimum moisture content (OMC) and then additional water is introduced. The effects of this additional water in the base course is evaluated to understand the effects of water infiltration due to seasonal variation even after the base layer is constructed. Blends of virgin aggregate (VA) and reclaimed asphalt pavement (RAP) were selected for this evaluation. The laboratory test results showed that the addition of water increases the permanent deformation and decreases resilient modulus (both adverse effects). However, samples with better drainage properties (i.e., RAP-VA blends) perform better than base course constructed with VA alone.

It has long been recognized that excess moisture in the pavement layer when combined with heavy traffic load and moisture-susceptible materials, can significantly reduce the service life of a pavement structure. So far, no pavement design guidelines can provide an accurate, robust, and dynamic infiltration-drainage model that is suitable for both saturated and unsaturated soils under different climatic conditions. This paper aims at proposing a new infiltration-drainage model that is suitable for both saturated and unsaturated soils. The proposed model is based upon Richards’ equation to govern the water flow in saturated and unsaturated soils, with an additional water source term to account for the influence of precipitation and the current water state within the soil. The calibrated model was used to evaluate the influence of rainfall intensity and duration on the drainage performance of a pavement structure.

Pumping is among the leading distresses in both flexible and rigid pavement. Pumping is defined as the ejection of water and fine materials of the pavement system under pore water pressure generated by repetitious traffic loading through larger voids or cracks. Pumping can significantly reduce the overall strength of the pavement, clogging the course material and eventually affecting pavement performance. Pumping requires heavy traffic loads, water, fine content in the lower layer, and no fine particles in the upper layer. Methods of limiting pumping include removing water, reducing pore water pressure, and separation of fine content from upper layers. The latter is investigated extensively in the literature. In this study, the reduction of water content as a means to reduce pumping is investigated. The drainage performance of a newly developed geotextile that can drain water both in saturated and unsaturated conditions has been compared to conventional drainage systems being used in pavements. For this purpose, a box filled with a granular pavement base material was instrumented and measurements of volumetric water contents were made to compare the effectiveness of each studied case. Results showed that the drainage ability of the newly developed geotextile is significant, specifically in an unsaturated condition, compared to conventional drainage methods being used in practice.

Inadequate subsurface drainage tremendously impacts pavement performance. Pavement foundation models in various degrees of superposition and complexity including the Winkler foundation model idealized as a dense liquid, the two-parameter Vlaslov model and the three-parameter Kerr foundation model are indispensable idealizations in the mechanistic-empirical design processes. These design idealizations of foundation types are confounded by undrained or poorly drained subsurface conditions of erodible base and subgrade materials associated cracking, faulting, and accelerated degradation of surface ride quality. In concrete pavements, in particular inadequately drained bases have caused surface joint-spalling, mid-depth joint-cavitation-induced-scouring, and bottom trapezoidal-erosion of the concrete. In addressing this challenge, research examined characteristics of a geocomposite joint drain (GJD) as a subsurface drainage material. This research showed that the numerous benefits of geocomposite joint drain are not limited to lateral stability under load, lateral transmissivity as well as ease of construction and reduction in overall pavement structural thickness.

Traditionally, classroom-engineering courses tend to emphasize theory, with limited integration of and application to real-world engineering practices. Additionally, students work mostly on their own, which limits their opportunities to learn the importance of working in a group and developing effective interpersonal communication skills. Employers want entry-level engineers to be sound technically and possess a variety of professional and interpersonal skills, so they can work effectively as part of teams to execute and manage actual projects, communicate well, and understand the economic, social, and political aspects of their professional activities. Engineers need these skills to maximize their importance and value in society and to fulfill society’s expectations of engineers. These professional expectations complicate engineering education in universities worldwide. This paper discusses components of an undergraduate engineering course taught at the University of New Orleans (UNO). The paper shows the importance of using actual, problem-based learning in the classroom, where students work in small groups under the direction of professional engineering practitioners, who serve as (1) supervising mentors to the students and (2) client representatives. This interactive, hands-on experience helps students understand better the application of theory in real-world projects, gain an appreciation for the business and professional practice aspects of engineering, and gives them opportunities to make valuable professional contacts. The mentors, on the other hand, enjoy giving back to their profession and, as a side benefit, they meet potential employees (and clients).

This study is a preliminary effort that aims to develop novel examples and in-class activities that convey geotechnical engineering concepts to students in a multidisciplinary way. A library of examples in eleven most common topics of geotechnical engineering has been established. Each example comes from one of five categories including engineering, science, history, global issues, and art. The examples and in-class activities for each topic are compiled in the format of slides for ease of use. To assess the effectiveness of this approach, a survey was designed and distributed to the students taking the “Geotechnical Engineering” class. Survey results highlight the importance of the study and provide insights into the future design of novel examples. This study is expected to promote critical thinking and result in greater retention of geotechnical engineering knowledge.

Engineering capstone courses often struggle to balance authentic design experiences with the need to develop project management skills and cover the ABET requirements. A senior design course implemented in the Department of Civil and Environmental Engineering at the University of California, Davis, employs a unique format to model a professional workplace. Geotechnical case study projects are developed in partnership with industry, which allows students to work with real geotechnical engineering site data and compare their final design to the actual design implemented. Students write a work plan in response to a request for proposals, develop preliminary designs, perform an alternatives analysis, and then develop a detailed design that includes sustainability considerations. This approach allows students to engage in and gain feedback on a project which requires technical depth as well as project management skills. This paper describes the development and implementation of the geotechnical engineering section of the course, lessons learned, and recommendations for programs considering similar courses.

The GeoExplorer project is an ongoing effort aimed at addressing educational gaps related to field testing and practical experience in geotechnical engineering education. A computer game-based module was developed to supplement traditional lecture techniques and take advantage of technology familiar to today’s students. To date, three different versions of the GeoExplorer module have been implemented at four different higher education institutions in the United States to 480 students in total. The final module consisted of a lecture to teach cone penetration testing (CPT) procedures and analysis using traditional methods and demonstration photos and videos as well as a virtual internship experience where context of the virtual field testing environment is provided through a mock internship with a fictitious company. In between implementations, instructor feedback and student surveys were used to iterate over the module and different existing curriculum to work towards our vision of a mixed reality game, one that blends existing curriculum activities with virtual ones. In this paper, we describe our initial impressions of the results of these implementations and reflect on differences in student learning gains on different campuses. The resulting insights shed light on the constraints, difficulties, and opportunities for game-based learning in geotechnical engineering education, particularly as it relates to building a module that is equally effective in fostering student learning in a variety of different classrooms.

While engineering outreach activities are numerous, many are unrelated to active areas of research in geotechnical engineering and fail to meet the needs of K-12 educators. Graduate students often practice communicating their research to technical audiences, but have less opportunities to communicate research to the public. A graduate course in engineering education was developed to address both of these needs. After introducing students to engineering education design and practice, students develop an educational module related to their research that meets relevant educational standards (e.g., next generation science standards, common core standards). Towards the end of the course, students implement their designs in a K-12 classroom, evaluate the results, and incorporate lessons learned into their final design. This paper provides an overview of the graduate engineering education course and details the development, implementation, and evaluation of a bio-inspired foundations module developed as a course project. The module was used to introduce a middle school class to concepts in bio-inspiration and sustainability through a hands-on example of active bio-inspired geotechnics research. The paper also includes a discussion of the impact of the course on graduate student development of teaching and communication skills and the alignment between K-12 educational standards and geotechnical engineering concepts.

Across most disciplines of engineering there continues to be economic, social, and political changes that merit a more comprehensive knowledge base for those pursuing careers in engineering. STEM education in general is often cited as a critical component to increase economic global competition by expanding the competitive edge in modern economies. In addition to technical skills taught at the university level, evidence from industry suggests a need to create an environment fostering a holistic engineering skillset that prepares students for a variety of engineering careers and accelerates their professional development. Data from surveys, interviews, and career fair observations revealed that non-technical skills such as writing, presenting, communicating, collaborating, leading, mentoring, and critical analysis have been identified as important by industry representatives. This paper discusses the efforts of one National Science Foundation-funded Engineering Research Center to strategically embed and adjust educational components to allow future engineers to learn, practice, and apply non-technical skills that enrich their university experiences.

In most undergraduate civil engineering degree programs, students start with a mechanics sequence in which physics concepts are applied to solve problems. In geotechnical courses, sometimes these physics-based concepts are de-emphasized in favor of focusing on empirical procedures used in practice. While such an approach certainly has its benefits, it can be argued that a well-founded background in fundamental principles can better equip geotechnical engineers to troubleshoot problems and extrapolate to achieving more innovative, resilient, and comprehensive solutions, in particular amidst the rapid rate of technological advance in other fields of science and engineering. Herein, the flipped classroom technique is proposed as one means to promote enhanced student learning of underlying scientific principles in geotechnical engineering. In the flipped classroom, students watch a short video “lecture” outside of class, availing time in class for group problem solving, instructor interaction, and anchoring of solution methods back to fundamentals. Two example applications are presented. Several positive outcomes have been observed: students demonstrate higher command of knowledge and are more interactive, engaged, and enthusiastic about geotechnical engineering.

Bivalve colonies are being explored regarding their potential contribution to erosion and scour mitigation. As a first step toward this goal, the in situ conditions of a tidal riverbed around an oyster reef in the Piankatank River in Virginia were investigated using a rotary side-scan sonar (SSS) and a portable free-fall penetrometer (PFFP), among other methods. The field survey was performed on October 4 and 5, 2018, in an area with a radius of approximately 300 meters in the direct vicinity of an oyster reef. The SSS results showed a significant increase (>20%) in the standard deviation of the backscatter intensity where the oyster reef was located, indicating an increased surface roughness. The PFFP results suggested somewhat of an increase of in situ peak friction angles with increasing proximity to the oyster reef. This correlation can be explained by an expected increase in sharp oyster shell fragments near the oyster reef. Thus, the SSS offered clear imaging and a measure of increased surface roughness of the oyster reef, while the PFFP provided insights into changes in sediment behavior in the riverbed surrounding the reef.

Sediments of coastal Louisiana contains silt clay alluvial deposits mixed with varying percentages of organic matter which are very compressible and erodible in nature. Coastal property development, sea level rise, geologic subsidence, loss of barrier islands, increasing number and intensity of coastal storms, and other factors have resulted in water quality degradation, wetlands loss, reduced storm and surge protection, ground settlement, and other challenges in coastal areas throughout the world including Louisiana. One of the goals towards re-establishing a healthy coastal ecosystem is to rebuild wetlands with river diversion or sediment conveyance projects that optimally manage and allocate sediments and positively affect the water quality. Engineering properties and material characteristics of the dredged material are input parameters in several mathematical models used to predict the long-term behaviour of the dredged material and foundation soil. Proper characterization of the dredged material and their settling properties is of utmost importance in the effective design of a coastal restoration and land reclamation project. This paper presents the results of several laboratory tests performed on coastal sediments containing varying percentages of organic content obtained from southeast Louisiana. The effects of organic matter on the settling characteristics of the dredged sediments used in coastal Louisiana marsh creation projects are discussed in this paper. A lower organic content generated higher settling characteristics for coastal sediments. The zone settling velocity was lower for dredged slurry with higher percentages of organic matter.

Seabed soil behavior under ocean wave loading is important to understand for the safety of coastal infrastructure, e.g., breakwaters, wind turbines, coastal armoring. A two-dimensional finite element model is generated in OpenSees to simulate nearshore seabed soil reaction to progressive wave loading by coupling pore water pressure and soil particle displacement. Wave loading is applied at the surface of a two-dimensional rectangular seabed domain as vertical pressure as well as pore water pressure. The numerical model is justified by comparing with analytical solution using different material parameters. A parametric study on model boundary effects shows that for the same wavelength wave, effective finite element domain size is not related to the full domain size as long as the lateral domain size is at least one wavelength. Soil liquefaction potential at different locations is studied with changing wave frequencies. A standing wave situation is also examined to simulate an ideally fully reflected wave in front of a coastal structure. The node and anti-node location of the standing wave greatly affect the liquefaction potential prediction. The results show that the wave properties are important for predicting soil liquefaction depth as well as liquefaction initiation time. Soil parameters like hydraulic conductivity and the elasto-plastic material behavior would also have the impact to the liquefaction region size and magnitude. This study provides a reasonable reference for further soil-fluid-structure interaction studies.

The Louisiana coastline experiences drastic levels of deterioration due to marsh edge erosion, pipeline and navigation channel construction, saltwater intrusion, and restricted sediment supply. The role of geotechnical properties as a driver of wetland behavior is underscored by the many studies on wetland loss, e.g., marsh edge erosion, shallow subsidence, wetland collapse, and uprooting. A modified piezocone penetrometer was implemented alongside soil cores to evaluate shear strength and hydraulic properties of the vegetated mats at two marshes in Terrebonne Bay, Louisiana. Based on the field measurements, the test method was found to be repeatable and consistent with the ASTM D5778 standard guideline. This study provides a geotechnical assessment of the two locations to better understand the implications of the root-soil matrix on wetland stability. The results show these marshes are supported primarily by an offshore sediment supply and a progression inland from the shore is accompanied by a reduction in soil strength.

The soil cement mixing technology (SCM) for soft ground improvement has been widely applied since 2000s in Vietnam. Recently, the SCM has been applied for the seepage cutoff of earth levees in the Mekong Delta. However, the permeability of soilcrete need further research. This study investigated the permeability of the soilcrete specimens made from the soft clay taken in the Mekong Delta mixed with cement slurry in the laboratory. The cement contents of 200, 250, 300, and 350 kg/m³ at the ratio w:c of 1.2:1 were used to examine variation of k_s and k_soil. The falling head—constant tailwater level method was applied for the both rigid and flexible wall permeameters. After 90 days tested, the results indicate that (1) k_s lower 100 times than k_soil; (2) k_s decreases with the curing time; (3) k_s decreases with increasing in cement content, but slightly increases at a cement content of 350 kg/m³; (4) the height of soilcrete specimens has unclear effects on the soilcrete permeability.

Hurricane Harvey, a category 4 hurricane on the Saffir-Simpson hurricane wind scale that approached from the Gulf of Mexico, caused severe flooding in Texas and Louisiana. Recorded water levels along the Brazos River exceeded historic high-water levels, and erosion and slope failures of riverbanks were observed in many locations along the river. A near-surface site investigation was conducted in the Brazos River along a short section in Sugarland, Texas, post-Hurricane Harvey. In situ tests were conducted using a portable free fall penetrometer and a chirp sonar. Results showed that sediment properties varied between different locations. Weaker sediments underlying a loose top layer were observed at both riverbanks reaching a penetration depth of ~20 cm, whereas stiffer sediments were found at the center of the river with an estimate of maximum quasi-static bearing capacity ranging from 25 to 300 kPa at sediment depths less than 7 cm. Particle size distributions varied as well depending on the location. Results suggest a correlation between sediment strength and backscatter intensity of the chirp sonar. In summary, in situ geotechnical properties across and along short sections of the Brazos River exhibited a significant variability, likely governed by the local sediment remobilization processes that was reflected in portable free fall penetrometer and chirp sonar measurements of the riverbed surface.

Phipps Peninsula is a sandy peninsula located near the town of Yakutat, Alaska. In the summer of 2018, a field study was conducted in three areas of the peninsula. All three locations feature complex sediment remobilization processes shaping the local geomorphology. Here, variations in geotechnical properties at the three test sites are investigated. For this purpose, a portable free fall penetrometer (PFFP) was deployed along several transects at the three sites, totaling approximately 750 deployments throughout the course of the study. Since field studies using PFFP on sub-aerial and intertidal beach areas are limited, and results are highly variable, novel methods were implemented for the analysis of the PFFP data. This study represents a first step towards the use of PFFP data to characterize geotechnical properties on sub-aerial and intertidal beaches. Temporal differences in strength are discussed in the context of local physical processes, and spatial variability was related to differences in morphology and hydrodynamics.

Coastal bluffs are at the intersection of land and seas. Thus, their failures and recessions are controlled by both land- and sea-based activities. Bluff recession imposes risks to structures and infrastructures and has environmental and economic consequences. Hence, it is critical to understand various processes influencing bluffs behavior, necessary for developing predicting tools and methods for future bluff recessions. We developed an experimental campaign to study the effects of fine content on the erosion and failure processes of predominantly sandy bluffs, bluffs that are composed of mostly sand and little fine contents. Bluff models of various soil properties underwent wave and surge actions in a wave flume. The responses of the bluffs to those “sea-based” activities were recorded and analyzed using image processing techniques. Then, the rates of beach erosion, and undercutting and recession of the bluffs were assessed against the fine content of bluff material. Our observations and analyses highlight the effects of fine content on the erosion of foreshore and instability and recession of bluffs.

On the majority of navigable waterways around the world, maximum ship vessel size is dictated by the size of the vessel that can be accommodated by depth limitations within access water bodies and port dimensions. For example, in the Americas, vessel dimensions are limited so that the ships may fit through the Panama Canal’s locks. These ships are known as “Panamax” vessels. In southeast Asia, maximum vessel dimensions are governed by the depth of the Strait of Malacca and hence are appropriately dubbed “Malaccamax” ships. In light of this, one of the design considerations for these restricted water ways and ports is potential soil erosion/scour near critical infrastructure due to main propeller or bow/stern thruster wash. The World Association for Waterborne Transport Infrastructure (formerly the Permanent International Association of Navigation Congress or PIANC) has published guidelines for designing scour protection for quay walls and revetments subjected to propeller and thruster wash mostly through the utilization of empirical formulations derived from physical modeling and field studies. While these guidelines are a constructive starting point for scour protection, in the future it is expected that computational fluid dynamics (CFD) models will be employed to more accurately estimate bed stresses for which the bed protection can be designed. In this study, several CFD simulations were prepared to investigate combined thruster and propeller flow around a representative berthed Malaccamax vessel using Siemens’ Star-CCM+. Results showed that bed stresses induced by the thruster close to the quay wall can exceed order 300 Pa and the highest bed shear stresses are caused by vortices associated with overcoming the inertia of the stagnant water near both the propellers and thrusters.

There has been a growing concern in recent years about the effects of anthropogenic noise due to pile driving on underwater wildlife. Current guidelines for mitigating hydroacoustic effects associated with these geotechnical events are based upon relatively simple transmission loss formulations. The advantage to these guidelines is that computing transmission loss using the prescribed methods is not labor intensive. But their disadvantage is that they may not take all variables into account when computing transmission loss—particularly the wave climate and/or local geotechnical information. Because of this, it may be possible to improve transmission loss computations. To better-characterize pile driving sound transmission loss, a unique in-water instrumentation system has been developed. This system consists of several hydrophone-equipped buoys that transmit sound data to a field team in real time via a wireless network. The sound data are also recorded onboard the buoys along with geospatial data and water temperature data at depth. Preliminary testing has been conducted using this buoy system at various water-based pile driving sites throughout Florida. Preliminary results show that transmission loss coefficients may be significantly higher than coefficients recommended using the Practical Spreading Loss Model.

Reliable estimation of strength development of cement stabilised clay is beneficial in optimising cement dosage to satisfy a target desired strength performance in land reclamation and ground improvement applications. Traditional strength predictive models often adopt either hyperbolic or logarithmic model to represent the evolution of strength gain over time. However, these models generally consider only a limited range of curing ages, offering inaccurate estimates at very early or late age phases. In order to present the complete 3-phase strength development of cement stabilised clays, involving the settling, active, and inert stages, a cumulative distribution function (CDF) of the log-normal distribution is introduced. Results show matching estimates of the measured strength development over a range of clays and cements using the novel CDF approach across an extensive database collated from long term experiments in several literatures.

Undrained strength of Lake Agassiz clays in the Fargo, ND, area have a relatively low rate of increase in strength with depth. When using automated optimization algorithms within limit equilibrium software for selecting a critical slip surface, a deep V-shaped wedge mechanism with a factor of safety 15% to 30% lower than a critical circle may be calculated. That optimized limit equilibrium surface may be disregarded as kinematically inadmissible; however, decisions would then be based on circular surfaces that may not be truly optimized. This paper compares limit equilibrium solutions for undrained embankment stability to a simple analytical upper bound, as well as to numerical upper bound and lower bound solutions, to aid in selecting the factor of safety for an appropriate optimized critical slip surface.

Evaluation of large numbers of diverse structures can be necessary for dredging and remediation along the waterfront. For large remediation projects, dredging may be needed along miles of shorelines potentially impacting hundreds of structures. The complexity of evaluating potential impacts poses unique problems for geo-structural evaluation. Modern tools such as databases and geographical information systems (GIS) offer the opportunity to consolidate data in complex ways to permit contemporaneous assessment of data from diverse sources and of diverse types. This paper presents the development of both conventional databases and GIS databases that include diverse data including tabular and graphical data. Georeferenced graphical data such as digitized geologic maps, soil survey maps, digitized historical aerial photographs, digitized fire insurance maps, property boundary maps, and contemporary aerial imagery can be overlaid and evaluated together with digital and tabular data sets. In this example, 3-dimensional point clouds generated by LiDAR and high-resolution sonar mapping were also linked in a way that permitted spatial evaluation in the third dimension to enhance the plan view imagery. Structures were identified through digital assessment of the imagery, together with the point cloud measurements for field reconnaissance. Field reconnaissance data was collected digitally in the field and uploaded to a web-based GIS database. Critical parameters for evaluation including dimensions, condition, geotechnical conditions were initially assessed and over 350 structures were classified and evaluated for potential zone of influence within which structures would be influenced by dredging activities. This assessment served as the basis for planning detailed investigations and preliminary definition of safe dredging limits. This paper will discuss the process and tools utilized, as well as, the bases used in the assessment and lessons learned using this approach.

During the spring of 1997, flooding in the communities of Grand Forks, North Dakota, and East Grand Forks, Minnesota, resulted in over $1 billion in damage and forced the evacuation of more than 50,000 residents. A $400 million flood risk reduction project is now complete providing protection against a flood with an annual probability of occurrence of 0.4%. The primary geotechnical design challenge was to determine a cost-effective, stable, flood barrier alignment in a region where landslides are a common occurrence. The Red River of the north meanders through the lakebed deposits of Glacial Lake Agassiz creating riverbank instability. Determining those areas affected by prior landslide activity and developing slope stability models that accurately define soil shear strength and groundwater conditions proved difficult. Some of the geotechnical design difficulties encountered and lessons learned over the course of this project will be discussed. An overview of the design and construction of a slope stabilization project utilizing prefabricated vertical drains and staged embankment construction will be presented.

Offshore wind turbines are exposed to high cyclic lateral loads induced by wind and waves which play a special role in the design of foundations. It's essential to clarify the bucket behavior under cyclic lateral loading to fulfil the design requirements of these foundations in both ultimate and serviceability limit states. In this study the behavior of monopods embedded in saturated sandy soil subjected to cyclic lateral loads were investigated using a sophisticated finite element model. The accumulation of permanent soil deformations and excess pore water pressure in saturated sandy soil due to cyclic lateral loading are taken into account by a fully coupled two-phase model combined with a hypoplastic constitutive model. Porosity-permeability dependence is modelled with the Kozeny-Carman relationship. The main focus was dedicated to loads levels that led to progressive failure, attenuation, and shakedown behavior under cyclic lateral loading. The main finding of these investigations are presented which make an effective contribution to the safe and economic design of bucket foundations.

Bridges supported by abutments on rock or end-bearing piles are not expected to settle. However, sometimes approach embankments to bridge abutments settle due to underlying compressible soil and/or traffic loading, causing bumps at the ends of bridges resulting from differential settlement between abutments and embankments. Climatic conditions including temperature changes and heavy rainfalls may also cause bumps. The seasonal temperature change generates expansion and contraction on bridge girders, which induce soil movements in the backfill behind the abutments. Heavy rainfall may cause erosion in the backfill when drainage systems are insufficient. In addition, improper design and construction may end with settlement of the backfill. This paper provides a comprehensive literature review and summarizes the internal and external reasons and mitigation techniques for bumps at the ends of bridges. The mitigation techniques are classified into five categories and compared in terms of their advantages and disadvantages: (1) bridges on shallow foundations supported by geosynthetic-reinforced soil (GRS); (2) use of lightweight fill; (3) use of approach slabs to create a smooth transition between bridges and embankments; (4) improvement of soft soils underneath embankments; and (5) stabilization of embankment fill.

The focus of this study was to evaluate the undrained shear behavior of filtered mine tailings and a tailings-dominated mixture of filtered tailings and waste rock (i.e., GeoWaste). Consolidated undrained triaxial compression tests were conducted on filtered tailings and GeoWaste. Filtered tailings yielded contractive, strain-hardening behavior. GeoWaste also exhibited strain-hardening, contractive behavior, and a modest transition from contractive to dilative behavior at an effective confining stress of 500 kPa. The undrained shear behavior of GeoWaste was comparable to filtered tailings at effective confining stresses of 50 kPa and 100 kPa. The undrained shear behavior of GeoWaste at an effective confining stress of 500 kPa exhibited enhanced shear resistance compared to filtered tailings, which was attributed to interaction between waste rock particles.

Erosion along the permafrost coasts has been accelerating, threatening the wellbeing of many Alaskan communities. This paper synthesizes and presents the engineering challenges, the costs of erosion control measures, and the remediation and prevention measures for permafrost coastal erosion through case histories. The review and synthesis of the state-of-the-practice of permafrost coastal erosion controls can be used to identify measures and construction materials that are proven effective in Arctic coasts. The synthesis shows that revetments built with rocks have the least reported failures and are the most common measures applied along the permafrost coasts. For seawalls, bulkheads, and groin systems, reported failures are mostly associated with displacement, deflection, settlement, vandalism, and material ruptures. The effectiveness of beach nourishment is inconclusive; only one successful beach nourishment project is reported in Alaska, but it is located outside the permafrost region. This study also shows that the unit cost of the erosion control measures in Alaska has continued to increase over the past 40 years.

Fly ash (FA) as supplementary cementing material (SCM) or a single binder agent can have two potential applications in mining. In this study the application of class C fly ash both as a single binder agent to improve the mechanical properties of tailings at the paste consistency and as an SCM to substitute Portland cement (PC) in cemented paste backfill (CPB) was evaluated through unconfined compressive strength (UCS) testing. Gold mine tailings were mixed with PC and/or class C fly ash at the initial solid content of 78%. Specimens were prepared by mixing tailings with 3% PC, 1.5% PC:1.5% FA, 1.5% PC:3% FA, and 7% FA binder contents and cured for 90 days maximum. The specimens with 3% PC and 1.5% PC:3% FA binder contents yielded fairly similar 90-day UCS values. The specimen with 7% FA binder content yielded a 90-day UCS value of 109 kPa. Vicat needle tests were performed to investigate the impact of PC replacement with fly ash in CPB on the initial and final setting times. The replacement of 50% PC with class C fly ash resulted in approximately 3.5 times longer initial and final setting times. Based on the test results class C fly ash can be successfully used to develop the most economical CPB mix design; however, longer setting time is needed. Moreover, the test results indicate a potential application of class C fly ash to be used as a single or major binder content to improve the mechanical properties of tailings at the paste consistency.

By 2023, global utility-scale solar photovoltaic (PV) installations are expected to reach almost 1,000 GW. Ground-mounted solar PV racking systems typically consist of a steel structure supported by drilled or driven pile foundations. Due to the relatively light-weight nature of solar racking installations, environmental conditions such as hazards due to frost action are of critical importance for PV ground-mounted systems. Pile uplift due to adfreeze stresses from frost action typically controls the foundation design for projects in the northern portions of the United States and in Canada. This paper presents a discussion of important considerations for geotechnical design for utility scale solar PV racking systems, with a focus on frost action risk, typical evaluation methods, design recommendations, and mitigation options for impacted sites. The important role of a typical design process including performing appropriate geotechnical investigations and incorporating results of pile load testing for optimization of design are also discussed.

Frost heaving is a major cause of damage to infrastructure in the seasonal freezing area. It is well known that the heaving is caused by the freezing of moisture migrated to the frozen front in response to the suction force instead of freezing of in situ only. Researchers have been trying to measure the suction force of the freezing soil and obtained a soil-freezing characteristic curve (SFCC) which is similar to the soil-water characteristic curve (SWCC) in unsaturated soils. However, a direct suction measurement in freezing soil is still a challenge. In this study, a high suction tensiometer (HST) developed for matric suction measurement in unsaturated soils was used to measure the suction in the freezing soil. Six thermocouples were installed in the soil to monitor the temperature variation of the different location of the soil. The experiment design, procedures are addressed in detail. The results revealed that 1) suction generated in the soil when water freezes during the freezing process, 2) HST can successfully measure the suction variation in the process of soil freezing, 3) suction increases dramatically when the water freezes to a certain degree, 4) temperature variation at the different location indicated that moisture migration happened in the freezing process.

The Trans Alaska Pipeline System (TAPS) was constructed in the 1970s to transport warm crude oil from Prudhoe Bay to Valdez over a distance of about 1,300 kilometers. TAPS traverses three major mountain ranges as well as continuous and discontinuous permafrost terrain. TAPS design was a major advancement in cold regions engineering and the system has outperformed its design life. Changing thermal conditions at isolated permafrost sites along TAPS have required increased maintenance and adaptations to maintain TAPS integrity and resilience for the next generation of operation. This paper presents three cases along the TAPS where the original design was no longer performing as intended due to changed subsurface thermal conditions and where Alyeska Pipeline Service Company implemented mitigation to ensure safe pipeline operation for many more years.

Managing the risk of differing subsurface conditions is never simple; however, when a design-build (DB) or public private partnership (P3) contract is awarded before a full subsurface investigation is completed, it becomes more complex. This paper reports a synthesis of the results of two projects that evaluated risk management approaches for subsurface issues related to geotechnical conditions and utility coordination. The projects identified effective practices for managing geotechnical and utility risk in construction manager/general contractor (CMGC), DB, and P3 projects. A toolset to expedite subsurface risk reduction is proposed. Effective practices are identified in the areas of enhancing pre-award communications on subsurface issues; the use of differing site conditions clauses; and aligning owner and contractor perceptions of subsurface risks as early as practical. The paper finds that contract language is not sufficient to transfer the risk of changed subsurface conditions. The owner actively must communicate all available subsurface information during procurement and pursue a strategy to reduce/retire subsurface risk expeditiously after award.

This paper evaluates how subsurface database management complements the traditional procedures and practices in geotechnical engineering. It explores new methods of geotechnical project management and delivery. It observes how the acquisition and storage of subsurface exploration data has advanced beyond handwritten paper archived in cardboard boxes to being collected and transformed electronically and stored in the compute cloud. This paper explores why all this advancement happened, what enabled it, and how it shaped contemporary geotechnical project delivery. The flow from raw field data to lab data, to data turned into information via reporting, to data represented geospatially, to data interpretation, interpolation, and extrapolation and, finally, data turned into 3D models is discussed and illustrated. The described data flow is used in building information modeling (BIM) and collaborative ecosystems shared among various stakeholders and across different geographical locations. Transformation in the way data has been handled was possible by shifting from an information ownership to an information stewardship mindset.