Geo-Congress 2019: Geotechnical Materials, Modeling, and Testing

The sudden loss in load carrying capacity of a soil specimen from its homogeneous material response is coined as the onset of instability or bifurcation in geomaterials. A numerical investigation of the coupled undrained (globally undrained, locally drained) transient analysis in Hostun RF sand under biaxial loading has been carried out in ABAQUS along with the implementation of a user defined generalized 3D nonassociative material model. Onset of localization has been probed by inducing material heterogeneity within the numerical framework. This requires a mesh convergence study for a given perturbation intensity. Numerically predicted instability onset strain becomes practically asymptotic to the theoretically predicted value with mesh refinement. The simulations revealed -that increased intensity of material heterogeneity induced in the sand specimens significantly reduced the bifurcation onset strain.

Simulation of plowing and cutting processes in soils is challenging and time-consuming due to large deformations and contact interactions. Recent studies on sand have suggested that a simplified, efficient approach based on incremental plastic analysis can capture the essential physics and features of the problem. The present study refines this technique by enhancing the kinematics and implementing a more sophisticated material law. The effects of hardening and softening, as well as dilatancy and compaction, are introduced. With the modified model, it is observed in the case of hardening (compaction) that the occurrence of multiple successive shear bands at variable locations gives the appearance of continuous shearing in the final pattern of deformation. This is markedly different from the previously predicted response in the case of softening (dilatancy), where shear bands appear at distinct locations and transition from one discrete location to the next. The computed results are compared with preliminary experimental data gathered in the Soil-Structure and Soil-Machine Interaction Laboratory (SSI-SMI Laboratory) at Northwestern University.

Structural backfills are one of the primary construction materials for critical transportation infrastructure projects such as geosynthetic reinforced soil structures, mechanically stabilized earth walls, railway beds, and other earthworks. A variety of approaches exists to numerically characterize the behavior of the well-graded and open-graded gravel aggregates that are commonly used in structural backfills. However, over-simplifications in modeling the behavior of such aggregates can omit some key aspects of their behavior, especially at very low effective stress levels. This paper describes the use of the single hardening model to simulate the behavior of structural backfills. The model is validated against a series of triaxial test results to accurately simulate the behavior of aggregate at low and intermediate levels of confinement. Modifications to the SHM are proposed that improve its predictive capabilities with respect to the deformation behavior of structural backfills.

The discrete element method (DEM) has been extensively used to capture the micro-mechanical behavior of granular materials. To reduce computational expenses and operate within the capabilities of DEM software, many DEM studies adopt idealized rounded particle shapes, which do not truly represent the angularity and surface texture features of sand particles. When in contact, the idealized particles become highly prone to rolling, which can significantly influence the shear behavior observed in DEM. To counteract this manifestation of artificial behavior, contact models embedded with rolling resistance mechanics have been employed in DEM simulations. Here, the angular features of realistic soil particles can be indirectly considered through a rolling resistance coefficient. In this study, the effect of rolling resistance on both macro- and micro-mechanical responses of granular material is examined through undertaking conventional undrained and drained triaxial simulations. The undrained and drained dilative behavior was found to increase with rolling resistance. However, the coordination number (CN) did not reflect this macroscopically observed behavior. Further, the angular velocity of DEM particles was observed throughout undrained shearing, where it was found that particle rotation tendencies can also be associated with dilative or contractive behavior.

The drained and undrained behavior of sand has been broadly investigated. However, the phase transformation (PT) state, i.e. the transition state between contractant and dilatant behavior has not got much attention. There are also arguments on how to define PT states and whether PT for undrained and drained conditions are equivalent or not. In this study, discrete element method (DEM) was used to evaluate the drained and undrained shearing behavior with particular attention to PT state under the critical state soil mechanics (CSSM) framework. It was found that the mechanical quantities e.g. the friction angle (φ), flow potential (u_F), etc. at the PT had good correlations with the state parameter (Ψ). In addition, such correlations could be also helpful to predict the PT state and constitutive relations of soils.

The use of lightweight deflectometer (LWD) to estimate the moduli of geomaterials for quality control (QC) of earthworks has gained attention among departments of transportation. The conventional method of estimating the LWD modulus is based on the assumption of a homogeneous linear-elastic half-space and a uniform stress distribution under the LWD plate. To account for the nonlinear behavior of geomaterials and soil-plate interaction, the results obtained from a dynamic finite element (FE) model was used to generate a comprehensive database containing the responses of a wide range of single- and two-layer geosystems with different nonlinear layer properties and top-layer thickness. An artificial neural network (ANN) model was trained to estimate the LWD moduli more accurately than the traditional layered elastic models. The proposed model improved the process of estimating the target modulus for compacted geomaterials with less simplifying assumptions and without the computational expense associated with the FE models.

A series of cyclic and monotonic constant-height direct simple shear experiments were conducted on a low-plasticity fine-grained soil mixture. The mixture exhibits fundamental behavior that is similar to that of typical clays, but also shows features of sand-like materials, such as high excess pore pressure ratios and developing large strains in a low number of loading cycles. This paper discusses key differences in predictions of two bounding surface constitutive models in simulating the cyclic behavior of the specimens tested in the laboratory. Numerical simulations were performed first, by a model developed for clays, and second, by a model developed for sands. Both models were calibrated using an advanced optimization technique to remove bias introduced by trial and error calibration methods. The comparison of the results of the simulations with laboratory test data shows significant differences and indicates that some fundamental features of the cyclic behavior of low-plasticity fine-grained soils cannot be captured by such models, suggesting it is necessary to develop more robust constitutive models for low-plasticity fine-grained soils.

It is well known that radial consolidation rate of drainage-installed soft deposit is closely related to discharge capacity of drains, which decreases with consolidation process. Conventional solutions were developed to consider the discharge capacity reduction using small strain theory, in which coefficient of volume compressibility and soil permeability were assumed to be constant. This paper formulates a general expression for consideration of discharge capacity reduction with time in numerical analysis, which based on the finite strain theory. The proposed solution was validated for a radial consolidation of large block sample. It is shown that the proposed solution yielded a good agreement with the measured results.

The exact heat transfer mechanism in the soil media can be understood by analyzing the soil behavior surrounding the heat sources. In literature, heat conduction has been considered as a main heat transfer mechanism in soil, and less attention has been given to the natural heat convection in saturated soils. There is only limited research in the literature which shows the presence of thermally induced pore fluid flow in soil media. It has been observed that heat convection through pore fluid flow in sand facilitates heat transfer in the ground. Therefore, both heat conduction and heat convection must be considered to accurately model the heat transfer mechanism in soil. In this paper, the presence of natural convection of water in a 2D axisymmetric domain of soil with a vertical heat source has been numerically investigated in steady-state condition. The soil thermal response and heat transfer mechanism for different soil types are compared. Feasibility of thermally-induced pore fluid flow is analyzed for different soil types. The results determine the presence of thermally driven pore fluid flow in high permeability soil (e.g., coarse sand) and confirm that the effect of heat convection in low permeability silt and clay is negligible.

In this research, a rate-dependent solid constitutive model capable of modeling granular flow behavior was employed with the smoothed particle hydrodynamics method (SPH). In comparison with the conventional methods using SPH in the framework of computational fluid dynamics, SPH method used in this study was simple and accurate. The developed model was verified with well documented experimental data of dry granular flume tests, and flow pattern and impact forces on rigid wall were investigated. The results of this study show the effects of inclination angle, initial soil deposition shape, and the distance between the flow origin and obstacle on the peak and residual force of the granular flow.

With the first high speed trains (HST) emerging in the United States, it is critical to develop better understanding of the design and performance requirements for HST track embankments. One of the main challenges in this process is to determine proper track embankment design criteria, specifically stiffness criteria to meet the acceptable deformation limits considering the maximum design speed. This study investigates the long-term deformations of HST track embankments on soft clay subgrades. The required thickness and stiffness (deformation modulus) for track embankment layers to meet the maximum deformation criteria were evaluated for a typical at-grade embankment section. A nonlinear, three-dimensional finite element (FE) model was developed to simulate the track embankment dynamic behavior under HST loading. Results of the FE analyses showed that the maximum settlement resulted from the train cyclic loading was around the typical criteria adopted for the existing HSTs. Variations of the settlements with train loading cycles showed that the plastic deformations accumulated within the first 10 cycles and after that became stationary.

On May 8^th, 1981, a gigantic sinkhole in Winter Park, Florida (USA), opened up mobilizing 250,000 cubic yards of soil, including extensive damage to two adjacent streets, a three-bedroom house, and car dealership. This catastrophic sinkhole has been referred to in the technical literature as the Winter Park sinkhole. When it stopped growing, the crater reached approximately 107 meters in diameter and 30 meters in depth, causing a devastating $4 million in damage to the community. Numerous site investigation efforts were performed in the vicinity of the sinkhole, and several geotechnical reports detailed the geotechnical characteristics of the site. In this study and for the first time, finite element based numerical investigations were conducted to elucidate the geotechnical failure mechanisms of the Winter Park sinkhole. PLAXIS 2D using the hardening soil small model (i.e., HSSmall, which captures small strain behavior of soils) was selected as the numerical platform for this study. Constitutive soil parameters were determined using published correlations and site-specific subsurface investigation data. Failure was triggered in the numerical model by incrementally increasing the size of a subsurface cavity until collapse of the model occurred. This analysis was aimed to assess the mechanical behavior of soils around cavities associated with stresses, strains, deformations, and excess pore water pressures. The shearing stress paths and evolution of ground surface deformations that triggered the geotechnical failures during the sinkhole formation are presented in this paper.

The characterization of seabed sediments is a crucial factor in geotechnical offshore and nearshore engineering, and there is an emerging need for more cost-efficient solutions. Free fall penetrometers (FFP) are designed to address this need, and to facilitate geotechnical in situ testing in subaqueous areas in a cost-effective manner. Soil parameters are deduced from different sensor suites, and in the case of small-scale, portable devices, often using only acceleration sensors and a pore pressure transducer. This leads to challenges in data interpretation associated with transient strain-rates, hydro-mechanical coupling between interstitial water pressures and soil skeleton, soil structure interaction, and a non-linear soil response during the impact. The material point method (MPM) represents a promising technique for this problem, because it can handle large deformations without mesh tangling, incorporate soil-structure interaction, deal with rapid impact processes, and simulate coupled hydro-mechanical problems. This study presents an initial numerical analysis of a FFP deployment, in which an advanced moving mesh technique is considered to optimize the accuracy of the results. The results are compared to data from controlled laboratory tests for validation, and the effects of mesh size are discussed.

A discrete numerical model developed for cohesive soils was utilized to study the thermo-mechanical behavior of a saturated kaolinite. The physico-chemical interactions that exist between clay particles, mainly van der Waal attractive and double layer repulsive forces, were considered. Van der Waal attractive interaction was modelled based on the hybrid Hamaker-de Boer-Lifshitz approach. Further, double layer repulsive interaction was modelled based on the Gouy-Chapman theory. A brief discerption of the implementation in a discrete element framework is presented. Moreover, the effect of temperature variation on the inter-particle forces, mainly the double layer repulsive force, is discussed. Finally, the thermally-induced pore water pressure generated during undrained heating of a clay sample was studied and validated against experimental data. The findings suggest that incorporating temperature-dependent interparticle forces in DEM simulations of cohesive soils will allow understanding the underlying thermally-induced micro-structural changes providing another insights and explanations into the observed large-scale behaviors.

The influence of soil dilatancy on the bearing capacity of a surface strip footing, situated on the edge of the reinforced cohesionless soil slope, is investigated by incorporating a non-associated flow rule in lower bound finite elements limit analysis. A single layer of reinforcement is laid at various depths below the base of the footing. The improvement in the bearing capacity of the strip footing is expressed by an efficiency factor which is the ratio between the obtained values of bearing capacity factor associated with the unit weight of soil for reinforced and unreinforced slopes. The variation between the efficiency factor and depth of placement of the reinforcement layer are presented as a series of design charts for various combinations of slope angle, soil friction angle, and dilative coefficient. By keeping other parameters as constant, the efficacy of reinforcement layer increases up to a certain depth of placement of the reinforcement layer, after that it reduces. The design charts indicate that the reinforcing efficiency enhances with an increase in the value of dilative coefficient. It is found that as the value of slope inclination and friction angle of the slope fill increases, the efficiency factor also enhances. Failure patterns are also provided for few representative cases.

Flat-plate dilatometer (DMT) and ASTM D 2435 consolidation test derived constrained moduli are compared and a utility analysis is performed. For the Northwest Corridor Express Lanes project along I-75 in Georgia, utilities (sewers, water lines, etc.) were expected to be affected by new embankment construction. Because of extensive sample disturbance incurred during sampling and testing of the Piedmont residuum soil, consolidation tests measured low constrained moduli and preliminary settlement estimates predicted large and unrealistic settlements. Additional DMT in situ tests were used to measure the constrained modulus with less disturbance. At critical utility crossings, the proposed embankments were modeled using PLAXIS 2D with soil defined by the DMT constrained modulus profiles. Settlement profiles from these modeled cross-sections were applied to the utilities using an elastic beam approach. The use of the DMT and elastic beam approach confirmed many of the critical utilities would not be damaged, thereby saving construction time and tens of millions of dollars in utility remediation and relocation costs.

Sand is extensively used in geotechnical engineering applications due to its abundance in the field. In general, sands are subjected to very low strain rates in most geotechnical engineering applications; however, during air or surface blasts, sands are subjected to high strain rates and their response needs to be studied in detail. The recent years have seen an increase in the usage of split Hopkinson pressure bar (SHPB) device to study the response of sand at very high stresses (on the order of MPa) and strain rates (10~1000/s). Researchers have shown that the particle size in sand influences its mechanical behavior at low strain rates. However, the effect of particle size on the stress-strain response of sand obtained from an SHPB device where particles are subjected to high strain rates is seldom studied. The particle size could also have an influence on the stress-equilibrium condition which needs to be satisfied by the specimen for the stress-strain analysis from the SHPB to be valid. However, the afore mentioned criteria are seldom studied and need to be studied in detail. In the current study, the SHPB device is modelled using a commercial software package LS-DYNA with a coupled finite elements-discrete element method. The sand specimens are modelled using polydisperse (spheres with varying sizes) and monodisperse discrete spheres. These simulations are used to understand the variation of stress-strain response of sand as a function of particle sizes. The study also provides insight into the effect of friction at the boundaries on the stress-strain response of the specimen. The results indicate that the specimen having larger polydisperse spheres provided similar stress-strain response as the specimen having smaller polydisperse spheres. However, the monodisperse specimen provided a softer response compared to the polydisperse specimens.

The presence of voids or karst features beneath rock-socketed drilled shafts can significantly diminish end bearing. However, very few methods exist to verify the presence of such anomalous features. Development of a stress wave non-destructive testing (NDT) method for in situ evaluation of conditions beneath drilled shaft excavations would improve quality control of these deep foundation systems in karst. However, development of such a system would need to address the potentially complicated stress conditions present at the base of excavations. The propagation of stress waves in soil and rock is influenced by the state of stress in the material, as manifested in their governing equations. Material modulus, velocity of waves, and the travel path of stress waves are in particular affected by the stress condition. Studies on the effect of anisotropy have been principally performed on small samples of soil and rock and there is limitation on the understanding of the effect of stress irregularity on wave propagations at larger scales. In this study, the state of stress and wave propagation underneath the bottom of drilled shaft excavations were numerically modeled to acquire a clearer understanding of the effect of stress redistribution on stress wave propagation. The initial results demonstrate the complicated state of stress at the bottom of excavations, where the gradient of stress changes rapidly up to the depth of one shaft diameter beneath its base. Details regarding the development of the numerical models, including material property selection, stress conditions, and wave propagation are provided. For the purpose of tomographic imaging, changes in the fundamentals of wave propagation can cause misleading results if unaccounted for when determining the velocity field beneath the drilled shaft excavation. A brief discussion on how the stress redistribution could potentially affect the imaging technique is therefore provided.

Instability of seabed due to wave action may cause serious damages to coastal infrastructure. The wave-induced instantaneous liquefaction near and around a structure, may impact the stability and capacity of foundation elements. The wave-seabed interaction has been mostly studied based on decoupled analysis for the flat or slightly sloping seabed (slope less than five degrees). However, some of marine structures, near shore may be built on (or anchored to) seabed with considerable slopes. In this paper, the response and instability of the sloping seabed supporting a marine structure and subjected to surface waves is evaluated. The scope included developing a numerical model using a fully coupled approach. Biot’s equations of the seabed in conjunction with governing equations for other domains (structure and fluid regions) are solved simultaneously using finite element method. The instability of seabed due to wave-induced instantaneous liquefaction around the marine structure is evaluated and the effect of slope on the extent of liquefied zone is examined. The results indicated that seabed response and the extent of liquefied zone near the structure are reduced with increasing steepness of seabed. The effect of various slope steepness and soil parameters on the extent of the liquefied zone is characterized and discussed.

The results of probabilistic analyses of a mechanically stabilized earth (MSE) wall with geosynthetic reinforcement are presented. The analyses consider spatial variability of reinforced and foundation soil properties using the 2D non-circular random limit equilibrium method (RLEM). In this study, it is assumed that the reinforced soil is a purely frictional soil, while the foundation is a cohesive-frictional (c-ϕ) soil. A negative cross-correlation between cohesion and friction angle and a positive cross-correlation between cohesion and unit weight, and between friction angle and unit weight are also assumed. It is shown in this study that, considering only random variability of soil properties results in an overly-conservative probability of failure for design. However, considering spatial variability of soil properties plus cross-correlation between soil input parameters provides an estimate of probability of failure which is in better agreement with the margin of safety implied using a deterministic factor of safety.

Traditionally, numerical studies on soil-culvert systems utilize two-dimensional (2D) finite element models (FEMs) to ensure minimized computational effort. 2D FEM adopts plane-strain assumptions—assumptions that miss the prevalent loading conditions in soil-culvert systems. The correct way of modeling such systems is to use full-scale three-dimensional (3D) FEMs. However, such endeavors have proven to be bulky both in computational time and memory needed to perform the analyses. In this study, the applicability of smaller-sized 3D models, to realistically represent soil-culvert systems, is scrutinized. Special types of elements, namely infinite elements, are employed to shrink full-size models by half. It was found that the use of infinite elements reduced computational time significantly while maintaining the accuracy of results and provided a more realistic time history in dynamic models.

The rapid depletion of virgin aggregate materials has proliferated use of alternative material such as recycled crushed concrete aggregate (RCCA) and reclaimed asphalt pavement (RAP) as pavement base material. However, based on the experimental results, strength is greatly affected due to the migration of fines from the subgrade and soil intrusion during road construction in the base materials. If the intrusion of fine particles cannot be controlled, a stiffness reduction factor should be considered in pavement design. The objective of the current paper is to develop a prediction model to evaluate stiffness parameter of recycled granular bases with intrusion of fine particles, using unconfined compressive strength (UCS). First, an experimental program was designed with varying percentages of untreated and cement treated RCCA and RAP which were mixed with soil samples in different proportions. Soil intrusion was allowed up to 24% based on the recommendation of Texas Department of Transportation (TxDOT) engineers. Secondly, linear statistical regression analysis was performed on the experimental test results, which were then fitted in a prediction model. Consequently, the UCS and M_R results were used to develop a prediction model using multiple linear regression analysis. The developed model suggests that there is strong correlation between M_R values and UCS.

This paper presents a field case study of in situ automated plate load testing (APLT) to evaluate the mechanistic properties of two foundation layer test sections constructed on Illinois Tollway pavement research test sections. One section consisted of nominal 102 mm thick aggregate subbase underlain by nominal 254 mm thick lime stabilized subgrade (LSS) over natural subgrade. The other section consisted of nominal 102 mm thick aggregate subbase over compacted subgrade. The foundation layers were designed to support a cement treated base (CTB) layer and continuously reinforced concrete pavement (CRCP). Testing was conducted to determine in situ composite resilient modulus (M_r) on top of the aggregate subbase layer, the individual layer M_r values, modulus of subgrade reaction (k) values on unstabilized and LSS layers, and permanent deformation (δ_p) characteristics on the aggregate subbase and subgrade layers. Results show that the pavement foundation conditions were highly variable within and between test sections [coefficient of variation (COV) values ranged between 39% to 63%]. Permanent deformation models were developed to estimate deformations under future trafficking. Stress-dependent universal M_r model parameter values were developed for comparison to typical laboratory M_r values. Falling weight deflectometer (FWD) testing was conducted after the pavement was constructed, and the backcalculated results suggest that the variability of the foundation layers is dampened by the stiffer CRCP and CTB structure.

Pavements founded on fine-grained subgrades subject to moisture increase are prone to severe distress shortly after construction. Moisture can reach the pavement foundation through various means including infiltration, capillary rise, lateral moisture transfer, and frost-thaw action. A recent advancement in the geotextile industry has led to the development of geotextiles with enhanced lateral drainage capabilities that can wick water out of the pavement section under unsaturated conditions. A laboratory test was conducted to quantify the moisture increase in the different pavement layers due to capillary rise from a nearby water table and to assess the ability of the wicking geotextile in decreasing the moisture from the system leading to an improved performance. Subgrade and base soil layers were compacted in a test box with acrylic sides. A hydraulic system was established to create a constant water level and allow for capillary rise. A laboratory testing program was conducted with conventional and wicking geotextiles installed at the layer interface and extended outside of the box. The moisture content was continuously monitored at different elevations using the time domain reflectometer technology. The results of this hydraulic setup showed a decreased moisture level in the pavement layers where the enhanced lateral drainage geotextile was installed.

Recycled concrete aggregate (RCA) results from the recycling of Portland cement concrete pavements. The use of RCA as aggregates on paving projects, where virgin quality aggregates are scarce, offers economic and environmental benefits. RCA is commonly used in the unbound base or subbase layer in pavements. Lower quality RCA (i.e., from D-cracked pavement) can be used in subgrade soil stabilization. In this study, a clay subgrade soil was stabilized using RCA and three different cementitious materials (lime, Class C fly ash, and a combination of Portland cement and fly ash). Clay soil-cement mixtures containing 0%, 50%, and 100% RCA, from two D-cracked concrete pavements, were designed following the United States Army Corps of Engineers method. The methodology uses standard Proctor compaction and unconfined compressive strength test results. These results indicate RCA, in conjunction with all cementitious materials except lime, improves the clay soil strength.

Geosynthetics are used in the pavement base/subgrade interface for possible benefits of filtration, drainage, separation to prevent base contamination, and subgrade reinforcement. The Virginia Department of Transportation has constructed two experimental sections using geosynthetics in Bedford and Albemarle counties that have been in service for 23 and 10 years, respectively. Recently, the Virginia Transportation Research Council conducted a follow-up investigation of the long-term performance of these sections. These sections were assessed using falling weight deflectometry and pavement condition ratings (i.e., a distress survey). In the Bedford project, sections with either geotextile or geogrid have a better structural condition than a section without geosynthetics. In addition, no evidence of contamination of base aggregate with subgrade clay was observed except for one segment with no geosynthetics and 4 inches (100 mm) of base. After 10 years, very little distresses was observed in the Albemarle project on both the control and geotextile sections.

Unbound aggregate utilized in base and subbase layers distribute the imposed load induced stresses to protect subgrade. Although the percentage of fines content in aggregates used for these layers rarely exceeds 20%, however, the behavior of aggregate skeleton is significantly influenced by the fines content characteristics. In this study, the effect of fines content (from 5% to 12%), plasticity index (from 5% to 9%), and dust ratio (from 0.4 to 1.0) of crushed limestone aggregate matrix on cyclic behavior of base and subbase layers are investigated. Cyclic tests are conducted to identify the resilient modulus, recoverable and permanent deformation of crushed limestone samples prepared at optimum moisture content with Illinois dense-graded standard gradation, i.e., CA 6. It is observed that fines content 12% is sensitive to permanent deformation and resilient modulus when the dust ratio is 0.4 and 0.6. However, at dust ratio 1.0, fines content 12% also showed effective response against permanent deformation and resilient modulus. With an increase of fines content from 5% to 12%, the permanent deformation increased and resilient modulus decreased when the dust ratio was 0.4 and 0.6, however, it behaved completely opposite at dust ratio of 1.0.

Hydronically-heated bridges are often used for bridge deicing with shallow geothermal energy extracted from underground loops as the energy source. Previously heated bridge designs are limited for implementation on new bridges since the heating loops are embedded within the concrete deck during bridge deck casting. This study describes the testing of an externally heated concrete slab under simulated environmental conditions. This heated slab consists of PEX pipes attached to the concrete deck bottom and encapsulated in geofoam for heat insulation. A fan was position at the top of the slab to create various wind speed over the test area. The temperature response at 1 inch below the slab surface was monitored under various wind speeds. The results show that there is a significant effect on the heating performance of the heated bridge deck due to the wind.

NASA’s soil moisture active passive (SMAP) satellite measures the near-surface soil moisture (0–5 cm depth) everywhere on Earth’s surface. It produces global soil moisture maps [in m³/m³] at the 9 km spatial and 24-hour temporal resolution. SMAP launched in January 2015 and has been collecting observations for a three-year period (2015–2018), with a 2–3 day temporal resolution. SMAP’s global soil moisture maps can be used to improve weather forecasts, increase our understanding of the water and carbon cycle, monitor droughts, and predict timing and location of floods. The radar observations could be superimposed on a map of transportation infrastructures to evaluate their performance under excessive water intrusion. This study included a analysis to evaluate the moisture-induced performance of transportation infrastructure foundations and pavement layers. The SMAP data were extracted within the study area before and during a major weather event. Other remote sensing products that monitor precipitation and groundwater changes were also employed to determine the level of infrastructure inundation. The results of this evaluation process suggest the feasibility of using SMAP data to investigate the performance of transportation infrastructure foundation layers under inundated conditions.

Pavements are subjected to many forms of stress during their service life including cracking and failures. Many of the failures can be attributed to poor subgrade, freeze-thaw cycle variations, and fatigue under repetitive axle loadings. Fatigue related cracking can lead to riveting, pot holes, and cracks in the wheel path, etc. One way to improve pavement performance is to enhance the mechanical properties of the base/subbase. This article describes the research on mechanical concrete comprising of waste tire-derived geo-cylinders filled with coarse aggregates to improve mechanical properties. Mechanical concrete helps in creating a more stable platform for the pavement system through confinement effects and distributes the stresses from axle loads to the ground and increases the subbase moduli. Some of the benefits of using mechanical concrete are cost effectiveness, savings in material and labor, and sustainability. This paper focuses on the presentation and discussion of laboratory test results conducted on representative pavement sections consisting of mechanical concrete with different tire diameters and its effectiveness in enhancing the pavement subgrade moduli under both static and fatigue loads up to 1 million cycles.

This paper presents first of its kind field testing results with frequency and stress controlled in situ cyclic plate load tests (PLTs) to assess the performance of geogrid stabilized base layer under asphalt pavements. Field testing was conducted on two test sections in northern Minnesota with and without geogrid stabilization in the base layer. Cyclic PLTs were conducted on a 304.8 mm diameter flat plate using sinusoidal loading at frequencies ranging between 1.4 to 0.01 Hz and three cyclic stress levels (931 kPa, 655 kPa, and 345 kPa). Comparison testing with falling weight deflectometer (FWD) was also conducted at three applied dynamic loads. Cyclic PLT data was analyzed to determine the frequency and stress-dependent in situ composite resilient modulus (M_r-Comp), back-calculated asphalt dynamic modulus (E^’_AC), and resilient modulus of the base (M_r-Base) and subgrade (M_r-SG). Statistical analysis of the cyclic PLT results showed that there is about 11% increase in the composite modulus in geogrid section than in control section. Similar analysis of the FWD test results did not show statistically significant benefit with the presence of geogrid. Statistical analysis of the cyclic PLT results indicated that the M_r-SG has the most influence on M_r-Comp followed by the presence of geogrid, and M_r-Base. E^’_AC has the least influence on the composite response.

Modulus of subgrade reaction (k) is widely used to evaluate subgrade strength and soil structure interaction, and design the rigid pavements. In the pavement ME design, the modulus of subgrade reaction is characterized by the dense liquid or Winkler model, which has no consideration of interface bond within the supporting media. To overcome this limitation, a modified subgrade reaction model is developed in this study to take into account the shear interaction between the concrete slab and base course. Formulation of the modified subgrade reaction model contains two steps: (1) transform the original slab and base system into an equivalent cross section based on the slab-base interface bond; and (2) develop a formula for the modified subgrade k-value using the falling weight deflectometer (FWD) defection patterns on the equivalent section. An artificial neural network (ANN) approach was employed to quantify the influences of pavement layer modulus, thickness, and bonding condition on the modified k-value. A three-layered ANN model was constructed with 1,296 different combinations of pavement structural properties, which included Portland cement concrete (PCC) slab and base thickness and strength properties, including slab, base, and subgrade moduli, and slab-base interface bonding ratio. The FWD deflection pattern for each combination was calculated using the finite element software ABAQUS. The results showed that the modified k-value increased directly with the increasing degree of bonding. In addition, PCC slab and base moduli individually changed the modified k-value significantly but the subgrade modulus had minimal effects on the k-value.

The adoption of recycled material in pavement construction results in the reduction of landfills and promotes the sustainable design of pavements. As the utilization of these materials as pavement bases is gaining increased acceptance, the recent mechanistic-empirical design guide (MEPDG) included crushed concrete and recycled asphalt pavement (RAP) as base layer material in the design process. In this process, an important step is to determine the minimum thickness of pavement that satisfies the design requirements. Therefore, this study aims at optimizing the rigid pavement thickness on the recycled base material. To this end, a series of pavement cases in Texas were modeled through local traffic, climate, and soil condition in M-E design software AASHTOWare, and the obtained data were imported in a developed machine learning method (hybrid genetic programming and orthogonal least squares, GP/OLS) for optimization and prediction of possible pavement cases. According to the results, the proposed computing technique is in more than 90% agreement with the existing pavement design procedures to estimate the thickness of rigid pavements on the recycled base layer.

This paper presents a methodology to compute bending moments and shear forces, etc., in geosynthetic-reinforced pavement on expansive soils. The geosynthetic-reinforced pavement, subjected to the heave/shrinkage-induced vertical displacement caused by the volume change of expansive subgrade soils, was formulated by following the Timoshenko beam theory. The virtual load method (VLM) was developed by applying a virtual load on the pavement to make the beam deflection equivalent to the heave/shrinkage-induced vertical displacement. The unknown virtual load was expressed as a Fourier series, and the Fourier constants were determined by employing the inverse theory for the identification of material parameters. As a case study, the virtual load method was applied to investigate the effect of geosynthetics on the research road FM-2 in Texas, USA. The geosynthetics in the pavement functioned as a reinforcement to reduce the pavement damage caused by the seasonal swell and shrinkage of the expansive subgrade soils.

Among the many strategies presently used for stormwater management, pervious concrete is of great interest since its high porosity increases groundwater regeneration. Despite its popularity, pervious concrete is not currently being used or studied in Lebanon. This study used local materials to determine an optimum mix design for pervious concrete for a sidewalk project in Jdeideh, Lebanon. Samples were prepared with various water to cement (w/c) and aggregate to cement ratios (A/C). A cement by-product (cement kiln dust) was also used in the mix design. Cylindrical samples of each mix were prepared and cured for 28 days then subjected to permeability and strength tests. Results showed the optimum mix design was A/C=4.5 and w/c=0.36. Several laboratory specimens were then prepared using the optimum mix design. Clogging tests were performed by placing sediments on the surface of selected samples prior to permeability testing. Findings showed permeability decreased as the amount of sediment increased. The optimum mix was used to build a 500 m test section in Jdeideh, a major city north of Beirut. Field testing (i.e., percolation test) is being conducted and core samples taken for lab testing. The test section’s performance will be monitored over the coming year.

Most of the pavements in North Texas are constructed over highly expansive clayey subgrade which are severely affected by seasonal swelling and shrinkage. The clayey subgrade soil swells as the moisture intrusion takes place and shrinks with the loss of moisture. Due to repeated swelling and shrinkage, the serviceability of the pavement is compromised along with the alteration in the soil properties. The monitoring of moisture variation in the unsaturated soil subgrade is therefore required to predict the changes in subgrade soil properties. The objective of the current paper is to evaluate the actual variation of moisture and suction in the pavement subgrade through field instrumentation and to correlate it with the pavement performance. For this purpose, a pavement site SH342 in North Texas was instrumented with moisture and suction sensors in the grassy side slope. Resistivity imaging was also conducted to obtain the continuous portrayal of the subsurface moisture condition. Additionally, an inclinometer was installed across the pavement to evaluate the deformation of pavement with time. Based on field data during the last two years, the increase in moisture content was up to 15% due to rainfall events while the suction values increased to 1200 kPa during dry summer.

Pumping in rigid pavement can be defined as a traffic-induced subgrade soil migration into an overlying subbase layer, and/or redistribution of materials under slabs. Pumping may reduce the service life of pavement. This study aimed to assess the effectiveness of a geotextile layer in reducing the upward migration of subgrade soil particles to subbase and increasing service life in rigid pavements. A one-third scale model mobile load simulator (MMLS3), an accelerated pavement testing (APT) device, was used to simulate the repeated traffic loading on a scaled simulated pavement representing a typical rigid interstate highway. Two tests with identical configurations were conducted, except that a geotextile layer was placed at the interface of subgrade and subbase in one of the tests. In this study, pumping at a rigid pavement joint was investigated. Results of the tests were then compared. Materials used for construction of the scaled pavements were selected such that they represented an in situ stress condition. It was realized that the amount of migration increased with increased number of loading cycles. After 1,000,000 cycles of MMLS3 loading, approximately 70% reduction in the amount of subgrade migration and 52% reduction in the severity of joint faulting were observed when using geotextile at the subgrade-subbase interface of the pavement. This indicated that a geotextile separation layer was significantly effective in mitigating subgrade soil migration and could extend pavement serviceability.

This case study utilizes the United States Air Force (USAF) and Department of Defense (DoD) to emphasize challenges and outcomes of fully implementing and leveraging asset management programs, executing preventative maintenance or rehabilitation, and incorporating new technologies or design methodologies into practices. The majority of the circumstances highlighted by the project case studies presented are inherently military, but they provide context that can be applied elsewhere, as many transportation engineers (department of transportation [DOT], municipal, or private) are facing similar issues in today’s fiscal and operating environments. Lessons learned from the examples provided are intended to help implementation of new research into practice. One key point made through the presented case studies is that implementation of pavements advancements can be heavily affected by other factors. Proper consideration of the overall operational scheme of an entity (e.g. DoD, DOT, municipality) is important when implementing research and should not be overlooked.

The recycled materials such as recycled crushed concrete aggregates (RCCA) and reclaimed asphalt pavement (RAP) treated with cement have been widely used as an alternative granular base in pavement construction in different states throughout USA. In the flexible pavement systems, the base layer contributes to the structural capacity, so, the quality performance of this layer is essential. However, presence and migration of fines from the subgrade into granular base may affect the strength and stiffness of flex-base. As such, the main purpose of this study was to examine the effect of fine contents in granular base materials in terms of strength and stiffness. For this study, RAP and RCCA were mixed in different proportions from 0% to 100% with different amount of soil intrusion varying between 0% and 24% with cement content ranging between 0% and 6% at 2% interval. An experimental program was designed and conducted to determine the optimum moisture content (OMC), maximum dry density (MDD), unconfined compressive strength (UCS), and resilient modulus (M_r) of the mixes of RAP, RCCA, soil, and ordinary Portland cement (Type I/II). Based on the experimental results, it was found that with the intrusion of fines in cement treated as well as untreated recycled granular bases, both the strength and stiffness decreased as compared with the same specimens without fine particles. With the addition of 12% and 24% of soil in the combination of 30% RAP + 70% RCCA and 50% RAP + 50% RCCA, the value of resilient modulus decreased in the range of 30–55% in the cement stabilized as well as natural forms. For example, the M_r value of (30/70) RAP/RCCA with 2% cement ranged between 69 MPa (10,000 psi) and 310 MPa (45,000 psi); it was reduced to a range of 69–207 MPa (10,000-30,000 psi) with 12% soil intrusion. Similarly, at 6% cement content, the highest value of M_r of (30/70) RAP/RCCA was observed as 517 MPa (75,000 psi) whereas with the 12% soil, the moduli value was reduced to 262 MPa (38,000 psi) at the maximum confining pressure of 0.14 MPa (20 psi).

Significant quantities of steel by-product materials are generated yearly worldwide. In their raw states, slag materials are considered unsuitable for reuse without processing. Since traditional storage and disposal strategies are neither environmentally friendly nor sustainable, their reuse as alternate materials can be economically and ecologically beneficial in various engineering and construction applications. This paper evaluates use of slag materials in roller compacted concrete (RCC) pavements. Slag materials were subjected to physical and chemical laboratory testing to determine their engineering properties. Twelve mix designs were developed and included graded slag aggregates, cementitious materials, water, and air-entrained admixtures to provide an optimal mix. The resulting optimal mix included 13% cementitious (50% Portland cement, 30% slag cement, and 20% fly ash). This study demonstrated the feasibility and beneficial reuse of steel slag materials in RCC pavements with potential cost savings at a former steel plant site in Maryland with over 5-million tons of stockpiles.

Accurate measurement of interface pressure between two dissimilar media is challenging in geotechnical practice, such as the pressure distribution between geosynthetic and subgrade soil. A commonly-adopted method of interface pressure measurement is the use of buried earth pressure cells (EPCs). However, EPCs can only make point measurements; therefore, they may cause stress disturbance due to their stiffness, and may compromise their accuracy due to their size relative to soil particles. A relatively new tactile sensor technology assures the use of thin and flexible sensors and allows the measurement of pressures at a large number of points that can generate a realistic normal stress distribution. This paper describes the assessment of a tactile pressure sensor for measuring the pressure distribution at the base/subgrade interface of a mechanically-stabilized layer with a multi-axial geogrid and a non-stabilized control section. The test results include the distribution of vertical pressures onto the subgrade, the change in the stress distribution while the applied vertical load was increased, and the stress concentration onto the subgrade.

This paper describes a holistic model to simulate the temperature, stress, and deformation in frozen soil. The model is implemented to simulate the induced stress and deformation due to frost action onto pavement. The frozen soil behaviors are based on a microstructure-based random finite element model, which holistically describes the mechanical behaviors of soils subjected to freezing conditions. The capability of the model in simulating the temperature distribution and volume change are firstly validated with laboratory scale experiments. Coupled thermal-mechanical processes are introduced to describe the subsoil responses subjected to sub-zero temperature on the pavement surface. This subsequently changes the interaction modes between pavement layers and leads to increase of stresses and deformations in the asphalt layer of the pavement. The mitigations methods are analyzed to prevent large deformation in the asphalt layer. The simulation results indicate that increasing the thickness of base layer or insulation layer are potential solutions for large deformation in the asphalt layer when the pavement is subjected to freezing conditions.

Assessment of pavement foundation layer in situ using mechanistic parameters such as stress-dependent resilient modulus can provide a validation of the input parameters assumed during pavement design. In this paper, results from a recent field study on the Illinois Tollway Elgin O’Hare Expressway construction project is presented. The project involved developing geospatially referenced validated intelligent compaction (VIC) measurements through a field calibration process using automated cyclic plate load testing, which produced coefficient of determination (R²) values of >0.9. The VIC measurements were obtained using an instrumented smooth drum vibratory roller that was programmed to output stress-dependent resilient modulus (M_r). VIC-M_r on a compacted subgrade and the overlaid granular layer are presented in this paper. The VIC maps and field observations revealed the compaction layers and pavement foundation materials to be highly non-uniform and to have built-in low stiffness “soft” areas and high spatial variability that are not necessarily addressed with conventional quality control (QC)/quality assurance (QA) observation and spot testing. The VIC maps on the unbound subbase layer showed reflections of the “soft” and “stiff” areas in the underlying subgrade.

Performance of a geosynthetic-stabilized base roadway founded over an expansive clay subgrade in Texas was evaluated over a period of 4 years. The construction involved three test sections. Two test sections were stabilized using two triangular geogrids of different characteristics and one test section was constructed without geogrid (control section). The geogrid layer was installed between a chemically-treated subbase and a flexible base layer. A comprehensive monitoring program was conducted to evaluate the performance of the roadway under environmental loads. Specifically, vertical movement of the roadway over time induced by recurring heave and settlement of the expansive clay subgrade was monitored. In addition, severity and extent of the environmental longitudinal cracks, identified as the main damage results from the expansive clay subgrade, were documented in each test section using data collected through rigorous visual condition surveys. Environmental conditions of the site, in form of changes in temperature and precipitation, was also closely monitored. Evaluation of the data collected on this roadway provided evidence for mechanisms that result in the development of environmental longitudinal cracks. In addition, comparison of the performance of the geogrid-stabilized test sections with the control section underscored the benefits from geosynthetic stabilization in mitigation of damages induced by the expansive clay subgrade. Furthermore, the observed difference between the performances of the two test sections stabilized with geogrids of different characteristics underscored the impact of geosynthetic characteristics on the benefits result from geosynthetic stabilization.

In this work, Corex slag, waste from iron and steel industry mixed with expansive soils and lime. The soil was blended with Corex slag in percentages of 10, 15, 20, 25, 30, 35%, and lime of 2, 4, and 6% by dry weight of soil. Apart from routine laboratory investigation, the cyclic triaxial test was conducted. Analysis using X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed the breaking the montmorillonite structure of expansive clay when it stabilized and led to the formation of stable calcium silicate hydrate (CSH) gel. The UCS value of the soil increased from 240 kPa to 989 kPa and the CBR value increased from 1.86% to 98.28% at the maximum. Laboratory resilient modulus (M_R) of the stabilized mix after 28 days varied from 195 MPa to 518 MPa.

The stability of a cavern excavated in the Chagrin shale was evaluated. During the excavation of the top heading, deformation of rock along the roof exceeded what is typically observed in rock cavern construction. The excavation sequence caused the increased deformations during construction due to rock disturbance. In addition, time-dependent rock deformations were observed during and after excavation. Several factors were believed to be the source of this time-dependent deformation including stress changes induced by the excavation, strain softening along the bedding planes, and creep of the shaley rock under compressive stresses. Finite element analysis (FEA) was carried out to simulate the rock conditions and sequential excavation due to the concerns regarding the unanticipated behavior of the rock mass. The FEA incorporated the bedding planes as observed in the cavern to evaluate the long-term deformations and stability. Rock mass behavior including time-dependent deformation was measured by means of rock surface convergence monitoring points (CMP) and multi-point borehole extensometers (MPBX). A time-dependent constitutive model was incorporated in the FEA to evaluate the potential long-term movement in the cavern. Creep tests were performed on core samples of the Chagrin shale from the wall of the cavern to estimate the time-dependent constitutive model parameters.

In 2003, Haley & Aldrich, Inc. was retained by Figg Bridge Engineers, Inc. and the Maine Department of Transportation to provide geotechnical services for the replacement of the Waldo-Hancock Bridge and associated approach roadways, which included the design of a concave, semi-circular rock slope that varied in height up to 100 ft along the Prospect approach to the Penobscot Narrows Bridge. During construction of the Prospect approach and excavation of the rock slope, several areas of the rock slope were identified as needing remediation. Between 2005 and 2016, 23 areas along the rock slope were judged to pose potential safety and long-term maintenance issues of varying degree. In 2016, MaineDOT approved and secured funding to remediate nine different areas of the rock slope judged to be “most critical” and “moderately critical.” Less critical areas will continue to be monitored and could be remediated during future phases of the project.

Empirical power-law model is usually used to relate the secondary creep rate and deviatoric stress for rocks. However, the effect of confining pressure on the secondary creep rate cannot be appropriately taken into account in the empirical power-law model and also has not yet been fully understood. Therefore, its ability for predicting long-term creep behavior of rocks under different stress state remains uncertain. In this study, the power-law creep model is applied to describe some creep experimental results available in the literature, first on a rock salt and then on a mica-quartz schist under different stress states. The results show that the power law model is able to describe and predict the secondary creep rate of the rock salt with a set of stationary model parameters. For the schist, however, the model parameters show an obvious tendency of confining pressure-dependency. A non-stationary power-law model is then proposed to better represent the secondary creep behavior of various rocks. Its ability of describing and predicting the secondary creep behavior of rocks is verified with the experimental results.

Laboratory estimation of elastic moduli of rocks is required in many engineering applications including infrastructure construction, slope stability analysis, mining, and energy technologies. Two mechanical tests, cyclic and multi stage elastic test along with concurrent measurement of P-wave and cross-polarized S-waves velocities were performed on a dolostone specimen obtained from a road cut in Shelburne, Vermont. While deformational response of the specimen was used to determine its static moduli, P- and S-waves velocities were used to determine the dynamic moduli (i.e. bulk modulus, Young’s modulus, and Poisson’s ratio). The rate of increment of static bulk modulus during hydrostatic stage was observed to be higher than that of the dynamic bulk modulus. Dynamic Young’s moduli were observed to be higher than the static moduli, whereas the dynamic Poisson’s ratio were smaller than the corresponding static ones. Moreover, the static Young’s moduli, during unloading cycle, were observed to be higher than the corresponding loading cycle. The results obtained in this study are in agreement with the previously published results.

Rock is one of the abundant materials widely used in the construction of breakwaters. Their performance is directly related to the durability of rock and its physical characteristics. In this paper, the durability and physical characteristics of eleven samples of rock masses used in the rubble-mound breakwater of Anzali Port, Iran, were evaluated to determine their service life. Suitability. Nine of these are igneous and the remaining two were sedimentary rock types. Standard tests such as Los Angles abrasion test, modified aggregate impact value, and Slake durability index were performed. The samples were classified based on the criteria provided by the Transportation Research Institute (TRI) of Ministry of Road and Urban Development of Iran. This classification, uses physical, mechanical, and chemical parameters based on indices. TRI criteria put samples into classes; for igneous rocks from A, the highest quality, to D, the lowest quality, and for sedimentary rocks and A to E. Rock quality is determined based on the scores that each sample attained for each test. The sum of these scores provides the total score of the sample. The results showed that the class of rocks used in the breakwater had wide variation in scores for suitability. In addition, it was found that sedimentary rocks to have the best properties for water absorption and porosity.

Temperature fluctuation in nature, either daily or seasonal, is capable of inducing a cycle of volumetric expansion and contraction of materials that are exposed to such an environment. Natural- and cut-rock slopes are also likely to experience such a cyclic temperature fluctuation. In many cases, however, thermally induced displacement of rock is not significant enough to trigger rock slope instability as the thermal strain remains in an elastic range. Nonetheless, there are multiple examples and observations that a number of rockslides were caused by continuous temperature changes. This work attempts to verify the perception that a repetitive temperature fluctuation can indeed invoke an accumulated slip between a rock slab and underlying rock slope, which may eventually lead to the rock slide. A numerical model of a thin rock slab sitting on a mild slope that is subjected to a repetitive fluctuation of temperature is simulated in this study, and it is shown that the slab gradually slides down with the number of temperature cycles. The described numerical simulation is validated via the comparison with laboratory experiments, which also showed the substantial accumulations of displacement as well as rockslides.

Sulfide minerals, such as pyrite, in black shale are sensitive to weathering processes, especially oxidation. The oxidation products are likely to produce an unfavorable effect on the structural properties of the rock mass. The chemical weathering of black shale causes geotechnical problems due to its weathering products, such as acid water and secondary minerals. This study investigated the geochemical characteristics and weathering behavior of black shale in southwest China. Black shale as well as fissure water samples from three sites in southwest China were taken to investigate the bulk chemical and mineralogical compositions, microstructure morphology, and hydrochemical characteristics over different degrees of weathering. The results show that pyrite contained in the rock could produce acid water during oxidation process, resulting in changes of mineral composition in black shale. The generation of secondary minerals, such as copiapite and rozenite, was observed in this study, which is likely to weaken the structure of the rock.

Injection and production operations change in situ stresses and cause deformations in confined geological reservoirs. A correct understanding of the spatiotemporal thermo-poro-elastic mechanisms is key to determine in situ stress state and interactions between a target layer and the sealing rocks. Previous analytical and numerical solutions are mainly obtained assuming the stiffness of the sealing medium to be infinitely large, as well as the rock temperature adjacent to the wellbore to have a discontinuous jump from an initial temperature to that of the heat source/sink. This paper presents new fully-coupled closed-form analytical solutions for thermo-poro-elastic pore pressures, stresses, and deformations within a confined geological medium. Winkler model is adopted to replicate interactions between injection layer and sealing media. Stress-path analysis is used to present temperature effects on principle plane variations near a thermal source under various confinement conditions.

This study focuses on the effects of drying on consistency limits. To observe the drying effects, samples for Atterberg limits were prepared (i) by starting from in situ moisture content without any drying, (ii) after drying at 60°C, and (iii) after drying at 110°C oven. When the samples were prepared by starting from their natural moisture content, the liquid limit values was 35% to 81% (1% to 26% higher with respect to the case of no drying) and plasticity index was 0% to 31%. Organic content of the samples were determined by loss on ignition test and were in the range of 4.3% to 12.1%. The mineralogy of the samples was investigated via XRD and SEM, and halloysite mineral was encountered. It is concluded that soils containing organic matter, and/or formed by weathering of volcanic rocks should not be oven dried when soil mechanics index tests are to be conducted, since their properties are significantly influenced due to irreversible dehydration.

Accurate estimation of soil mechanical properties represents a crucial step for most engineering applications. Both in situ and laboratory testing fundamentally rest on mechanically deforming (actuating) the material and simultaneously measuring its response in terms of displacements and stresses (reactions). Facing this widely adopted scheme, key questions remain unanswered: 1) what is the optimal type and/or mode of actuation that can most effectively extract soil properties; 2) what types of measurements are most useful for inferring material constants? As a first step in the investigation of these questions, an inverse model for the direct simple shear (DSS) test is constructed, wherein measurable responses are used to back-calculate soil properties. Specimens with two different aspect ratios are considered to study the influence of the deformation mode. The effect of the choice of measurements (i.e., which displacements and/or stresses are observed) is explored by assessing inverse model performance considering the DSS test as a boundary value problem, with variable displacement and stress fields, versus the conventional interpretation as an elemental test. Parameter sensitivities and correlation coefficients are employed as quantifiable metrics to compare material characterization based on different aspect ratios and types of measurements, and to interpret the performance of inverse analysis.

A complex-impedance measuring instrument (CIMI) is a relatively new non-nuclear device for measuring unit weight and moisture content of soil for QA/QC testing. The device is more commonly known by its manufacturer trade name, the “electrical density gauge” (EDG). A CIMI uses a series of electrical measurements correlated with measured in situ soil properties to create a soil model to infer in situ soil unit weight and moisture content. From previous research performed investigating the CIMI, the authors have identified that soil temperature influences the electrical measurements recorded by the device, and that the proprietary temperature compensation algorithm provided by the manufacturer does not always improve results. In order to evaluate the effects of temperature on the electrical properties measured by a CIMI, a series of tests under various temperature gradient cycles were performed on soil specimens in large Proctor-type molds, and the electrical properties of the soil were recorded by the CIMI throughout these tests. This study provides a new data set to illustrate how temperature can affect CIMI measurements, which can be useful for developing improved temperature correction algorithms for the CIMI in the future.

The Yazoo clay is highly expansive in nature and extended over central Mississippi, Alabama, and southern Louisiana of United States. The expansive clay soil undergoes shrink-swell behavior due to seasonal moisture variation and weathering. Due to the high shrink-swell behavior, the shear strength of the soil reduces to fully soften or residual shear strength, which eventually leads to slope failure in this area. This phenomenon is very common in Jackson metroplex area in Mississippi and which cause damage to roadway and embankments. The current study investigates the changes in shear strength of the expansive Yazoo clay. Undisturbed specimens were used for the peak and residual tests with an effective normal stress of 25, 50, and 100 kPa, and then sheared under drained conditions. A shear displacement rate of 0.0025 mm/min was used to ensure drained conditions. For the fully softened shear strength, normally consolidated soil samples were constructed from a slurry mix, in accordance with the U.S. Army Corps of Engineers test procedure. The residual shear strength of the expansive soil was determined based on repeated loading direct shear test. The test results also indicated that the highest shear strength (c=18.4 kPa and φ=20.2^o) was determined with the peak shear strength test, whereas the residual test generated the lowest strength (c=2.5 kPa and φ=10.5^o).

A custom made triaxial apparatus that can measure electrical resistivity at any stage of a triaxial test has been developed for determining the feasibility of establishing correlations between electrical resistivity and soil properties. Reconstituted golden flint sand and kaolin clay specimens are tested in consolidated drained (CD) and undrained (CU) conditions, and about fifty measurements of electrical resistivity were made for each test to shed light on how the electrical resistivity changes from specimen mounting to the end of shearing. The results show that electrical resistivity changed on the order of 10⁴ times during the water flushing stage of sand specimens and that resistivity decreases with an increasing degree of saturation. Depending on the soil type, clay or sand, electrical resistivity increases or decreases with an increase in mean effective stress during the consolidation stage. For the investigated soil types, using saturated saline at a defined salt content as the pore fluid, two empirical correlations for predicting the drained friction angle or undrained shear strength are established. These findings imply that the electrical resistivity can work toward advancing characterization of soil properties.

The Yazoo clay is dominant in the central Mississippi and neighboring states. This clay consists of very expansive characteristics and undergoes volumetric changes due to wetting or drying under different seasonal variations. Even though the Yazoo clay causes significant problems to the infrastructures in the southern states of the United States, limited research has been conducted to date on the volumetric changes of the Yazoo clay. This study investigates the change in the void ratio of Yazoo clay under a series of wet and dry cycles. Reconstituted Yazoo clay specimens were used for the experiment. The samples were subjected to 3, 5, and 7 number of wetting and drying cycles in an enclosed chamber for 24 hours period. During the drying process, the temperature ranged from 120–125 deg. F to simulate the typical high summer temperature of Mississippi. The axial deformation of the samples, as well as the change in void ratios at each cycle, were closely monitored. The test results indicated that the void ratio increases with the increase of wet and dry cycles and causes an overall reduction in the shear strength.

This study examines frequency effects on low-strain shear modulus and damping for 12 clayey and silty soil samples. A series of torsional shear tests were performed at frequencies ranging from 0.001 and 5 Hz. Soil samples with a range of plasticity were tested and results were normalized with the results measured at a frequency of 0.5 Hz. With a few exceptions, the shear modulus is lower at very low frequency ranging from 0.001 to 0.05 Hz, then become constant at frequencies ranging from 0.05 to 1 Hz, and increases as the frequency increases to 5 Hz. The damping measured at 0.001 Hz was found to be 2 times higher than the damping measured at 0.5 Hz. Similar to the shear modulus results, the damping is relatively constant at frequencies ranging from 0.05 to 1 Hz and increases as the frequency increases up to 5 Hz. Overall results show that frequency effects are more pronounced for high plasticity soils especially at low frequencies.

The resilient modulus (M_R) is used to represent the subgrade soil stiffness and is one of the key parameters for modeling pavement permanent deformation and subgrade rutting in the mechanistic-empirical pavement design guide (MEPDG). However, soils having good resilient modulus may or may not have small permanent strains under repeated loading. Therefore, it is necessary to study both the resilient and permanent strain characteristics of subgrade soils under repeated loading. In this study, repeated load triaxial tests were performed following AASHTO T307 on remolded soil samples collected from different regions of South Carolina. The samples were prepared at optimum moisture contents (w_opt) and ±2% w_opt. Resilient modulus and permanent strains of subgrade soils were measured under different repeated deviatoric loads and confining pressures. Statistical models were developed to correlate resilient modulus model parameters (k₁, k₂, k₃) and permanent strain model parameters (α₁, α₂, α₃, α₄) with soil index properties. Results showed that the compaction and optimum moisture content (w and w_opt), percent passing No. 4 sieve (P₄), maximum dry density (${\gamma }_{d_{max}}$), uniformity coefficient (C_u), liquidity index (LI), and specific gravity of soil (G_s) have statistically significant effects on the resilient modulus model parameters and the permanent strain model parameters for South Carolina coarse grained soils. The correlation between M_R and permanent strain suggests that M_R is a satisfactory soil property to explain permanent deformation or rutting characteristics for the South Carolina soils studied herein. Thus, permanent deformation for these soils can be predicted from index properties using MEDPG with the developed resilient modulus model, or directly using the developed permanent strain model.

This study reports laboratory investigations designed to help the understanding of the mechanics of the fatigue crack propagation in stiff clay samples under dynamic loading. To this end, prismatic samples of brittle clay with one pre-existing crack were subjected to uniaxial cyclic loading conditions. Results indicate that: (a) the repeated loading and unloading of fissured clays at a particular stress level leads to larger deformations than those obtained if the samples are subjected to a single cycle of loading; (b) the number of stress cycles needed to cause crack propagation depends upon the inclination of a pre-existing crack; and (c) crack propagation occurs in the samples at levels of cyclic stress that are well below the levels of the monotonically increased stress that also causes crack propagation in the samples. Thus, crack propagation can take place in clays at low levels of cyclic loading (fatigue).

Many geotechnical applications benefit from advanced analysis of flow through porous media, such as filter and drain design, internal erosion and piping, and liquefaction, among others. In this study, a novel method is presented to visualize key components of fluid flow through pores of a saturated synthetic transparent granular media representing natural sand. Images of sand particles were captured using a dynamic image analyzer. 3D printing was then used to produce 2D extruded scaled models of representative particles that were used as casts to produce transparent extruded particles made of polyacrylamide hydrogel. Planar (i.e., plane strain) models having controlled porosity were prepared. Steady-state flow was established through the soil model, from which high-resolution images were captured. Image analysis methods were then used to visualize the flow field in the interstitial fluid. In order to capture the fluid flow, the pore fluid was seeded with highly reflective silver-coated hollow micro-spheres. A laser light source was used to illuminate a plane within the model. Particle image velocimetry (PIV) was employed for visualizing inter-particle fluid flow fields. The method allowed for investigating soil-fluid interactions of scaled hydrogel Ottawa sand and angular sand.

The primary objective of this paper is to investigate the relevance and to quantify the influence of the specimen dimensions on the tensile and compressive behaviour of the cement treated base materials. This objective was achieved by post processing of laboratory measured properties of over 50 fabricated specimens coupled with numerical simulations to quantify the compressive and tensile strength properties in the UCS and IDT tests. The trend analysis of laboratory data underscored the influence of the specimen dimension, characterized by length to diameter (L/D) ratio on the strength properties of cement treated reclaimed and virgin mixes. Additionally, several numerical simulations were conducted to study the role of the bearing strip on the stress distributions in the IDT tests. The simulation results were further validated by laboratory tests to demonstrate the simultaneous influence of the (L/D) and loading strip on the tensile strength of the cement treated materials. Primarily, the UCS test results indicated that the unconfined compressive strength decreases appreciably with increasing length-to-diameter (L/D) ratio. The laboratory validated results showed that the adjustment of the loading strip can potentially minimize the variation in the tensile strength of cement treated materials in the IDT tests.

Sandy hemipelagic calcareous sediments are quite complex soils. In some instances, they can consist entirely of the skeletal remains of microorganisms, such as foraminifera tests. These calcium carbonate test (shell) producing protozoa are common in marine environments, accounting for the majority of the calcium carbonate in the open ocean. Foraminifera come in a variety of species, each with unique test morphological adaptation suited to their local environment. For example, planktic species have relatively low density tests and live in the water column, while benthic species have dense shells and live on the seafloor. This paper explores the impact of biologically driven morphology on the physical properties (e.g. crushing) of calcareous sand from the Browse Basin, offshore North West Australia. X-ray microtomography scans were performed to visualize and measure the test structure and the Weibull statistic of particle strength for Trilobatus sacculifer, a common planktic foraminifera, and Cibicidoides sp., a benthic foraminifera. These are compared with clastic siliceous and calcareous sands. Overall it is shown, that the biological taxonomy can play a significant role in the crushing behavior and mechanical properties of deep sea calcareous sediments.

Consolidation testing is a common means of approximating the settlement of clayey soil by applying compression and recompression indices. Regardless of significant improvements both instrumentally and methodologically in the acquisition of soil characteristics, geotechnical practitioners frequently are urged to use empirical models to evaluate the compression/ recompression indices due to the lack of consolidation tests. The key advantage of applying such functions is embedded in their simplicity and minimal incorporated parameters—for instance, moisture content, liquid limit, or void ratio—which are readily obtained from laboratory tests. Moreover, the necessity of accurate optimization of appropriate empirical models with consolidation test results encourages the application of more sophisticated techniques such as Bayesian probabilistic approach. This work eventually aims to introduce the best fit of new proposed empirical models to 95 available consolidation test results across the Dallas/Fort Worth (DFW) area, Texas. Fine grain soils located in DFW area, are predominantly over-consolidated and well-known for their expansive behavior with noticeable swelling/shrinkage capacity. After obtaining stationary condition, the first and second order of statistics encompassing the correlation structure amidst the model variables are attained and presented. To validate the results of the acquired variables, a comparison between different published empirical models is performed, and the associated coefficient of determination is illustrated.

Majority of geotechnical guidelines for chemical stabilization of subgrade/base materials for pavements use unconfined compressive strength (UCS) in establishing the optimal amount of additive. Laboratory determination of UCS strengths for these stabilized soils involves multiple trials by varying amount of stabilizers to achieve target strength. This process takes copious amounts of time, energy, and workforce. In addition to that, these trials are generally made on few discrete field samples which may not be representative of the overall site. Therefore, this study is aimed towards minimizing the laboratory work along with aiding in improving the sample collection strategies by using machine learning models. For this study, statistical classification was chosen to estimate optimal additive type and content. This method was used to classify whether soil will pass or fail a target strength requirement for a given amount and type of treatment. Logistic regression (LR), discriminant analysis (DA), k-nearest neighbors (KNN), and support vector machines (SVM) were used for this purpose. Commonly measured soil properties such as Atterberg limits and gradation [reported in databases such as Soil Survey Geographic Database (SSURGO)] along with treatment amount and type were chosen as predictors and, treated UCS strength as a response. Prediction accuracy was calculated using the area under the curve (AUC), correct prediction rate, true positive rate (TPR), and false positive rate (FPR). Optimal model was reported after model development using 5-fold cross-validation.

Natural soil deposits that contain diatom microfossils are found in many locations around the world. These deposits were formed in marine or freshwater depositional environments. The presence of diatom microfossils affects soil properties, such as the water content, Atterberg limits, and density because of the frustules’ very large intraparticle porosity. The presence of frustules within a saturated fine-grained soil matrix may lead to greater or much greater compressibility of the soil; however, the deformation mechanisms are not well understood. This paper presents and discusses the results of oedometer tests on two preconsolidated specimens, one composed of kaolin mixed with 40% diatomite (by dry mass) and another composed solely of crushed diatomite. The oedometric behaviors of the kaolin-diatom mixture and diatomite specimen are compared to consolidation test results on kaolin. Observations are consistent with particle (frustule) breakage as an important component of the vertical deformation and source of irrecoverable deformation during unloading. The results indicate that vertical deformations derived from other mechanisms in addition to primary consolidation in soils with diatom microfossils are dependent on the applied effective stress level.

Coupled thermo-hydro-mechanical (THM) processes are of great importance to geothermal, hydrology, and geotechnical engineering applications. There is a lack of laboratory testing apparatuses to measure the THM processes under controlled true 1-D heating conditions. This paper develops a modified 1-D heat soil cell for the study of THM processes. This soil cell consists of a double acrylic test column and a heating plate at the bottom plate to control the temperature gradient. The test cells are equipped with thermocouples to monitor the temperature changes during heating processes. Two tests are conducted with the boundary temperatures at 50 and 70°C, respectively. Test results show nearly linear axial and radial temperature profiles in the inner soil column. The temperature profiles for the outer soil column are also obtained, showing a significant influence of room temperature on the outer column. The time to reach steady-state temperature for both tests is the same, which is 6 h. A infrared camera was also used to visualize the temperature distribution of the column top surface.

Two methods to account for strain rate dependence of clay behavior in computing settlement due to consolidation and secondary compression are compared. The first method explicitly accounts for strain rate effects during primary consolidation using a visco-plastic relationship and nonlinear finite difference solution. The second method indirectly accounts for strain rate effects during primary consolidation by using analytical solutions for consolidation and secondary compression in combination with a time-line based procedure for selecting the analysis parameters. The second method is computationally simpler, and potentially useful for more complicated soil layering and loading conditions. These two analysis methods are described, along with a third, traditional approach for comparison. Results are presented for one-dimensional analyses of a single clay layer for a range of stress history and loading conditions. The time-line based method is shown to provide a reasonable approximation of the more rigorous nonlinear analysis method, indicating that various traditional analysis methods can approximately account for strain rate effects (or creep) during primary consolidation through the appropriate selection of input properties.

The mechanical behavior of soils is typically interpreted based on their response to applied stress during shearing. Several hyperbolic stress-strain relationships have been developed for use in non-linear incremental analysis of soil deformations. It is noted that the bulk electrical resistance of the soil changes with respect to its deformation. This phenomenon reveals the possibility of modeling deformation behavior of the soil based on changes in bulk electrical resistance. This paper proposes a methodology to model stress-strain behavior of the soil under unconfined load by using the change of bulk electrical resistance of the soil. A hyperbolic model was developed in which the change of stress is predicted based on the change of electrical resistivity of soil cylinder during axial deformation. This approach predicts the entire deformation process of the soil under unconfined compression load, without needing to conduct an entire unconfined test.

The axial load capacity of a driven pile is influenced by the properties of the pile-soil interface and the surrounding soil. These two are highly affected by the degree of saturation or the corresponding matric suction of the soil, which varies with climatic parameters such as rainfall and evapotranspiration as well as water table depth. In this study, a new framework for coupling the site-specific climatic parameters and water table depth with geotechnical parameters is proposed based on unsaturated soil mechanics principles to accurately compute the axial capacity and settlement of driven pile. The results show that the pile skin resistance, tip resistance, and ultimate axial capacity obtained from the proposed coupled geotechnical-climatic method are almost 160%, 80%, and 130%, respectively greater than those computed using the conventional method which assumes that the subsurface soil is fully saturated. Furthermore, the elastic settlement computed from the proposed method is approximately 40% smaller than that of conventional method.

The hydrologic performance of evapotranspiration (ET) cover system for waste containment is significantly influenced by the hydraulic characteristics of cover soil such as saturated hydraulic conductivity (K_s), unsaturated hydraulic conductivity (K_Ψ), and soil water characteristic curve (SWCC). Due to environmental and field exposure conditions like freeze-thaw effect, wetting and drying cycle, plant root growth and death, along with animal and insect burrowing, these hydraulic properties of cover soil are highly susceptible to variation. Therefore, assessment of the changes in these soil hydraulic properties is vital for the evaluation of long-term cover performance. In this study, the hydraulic properties of ET cover soil were evaluated for three years of environmental and field exposure. The uniqueness of this study is highlighted by the non-destructive methodology, as destructive soil sampling was avoided to preserve the integrity of the cover system. Consequently, this study investigates the changes in the soil hydraulic properties based on field instrumentation and in situ testing in large-scale lysimeters constructed in the city of Denton landfill. Moisture and temperature sensors along with tensiometers were installed at the site in planned depth intervals. A Guelph permeameter was used to determine the field saturated hydraulic conductivity. The field investigation results indicated that K_s increased nearly 400 times the initial measurement, Van Genuchten’s α parameter increased by a factor of 41, and the n parameter decreased approximately 1.25 times the laboratory measured values after a three year span of field exposure. The results from this study establish the effect of hydraulic characteristic of soil on the cover hydrology and the potential implications for design considerations for long-term performance of the ET cover system for waste containment.

Rain gardens are an effective type of stormwater control measure (SCM) used in developed areas to reduce runoff and replicate pre-development conditions by restoring the hydrologic cycle. The volume of water is controlled by infiltration and evapotranspiration. Percolation, which is sometimes referred to as deep infiltration, occurs deeper within the subgrade or underlying soil and is affected by the presence/absence, location, and design details of an underdrain; the thickness of soil media (typically imported engineered media); and the type and thickness of the native soils. Underdrains, when used, consist of a perforated pipe surrounded by coarse aggregate; they are often wrapped by a geotextile to prevent clogging. To investigate the influence of these factors, the hydraulic performance of a rain garden located at the headwaters of the Jenkintown Creek in Pennsylvania was monitored and modeled by using HYDRUS 2D. The rain garden, which has an underdrain, was installed in 2015 at the Abington Friends School in Abington, Pennsylvania. After construction, the rain garden was instrumented with a weather station, bubblers to measure the water level inside the bowl, soil moisture sensors, and a pressure transducer to measure outflow from the underdrain orifice. The water level from the bubbler and the local soil properties were used as inputs in the HYDRUS 2D model. The measured outflow was used to calibrate the model. The calibrated model was used to examine several scenarios such as the optimal size and location of the underdrain and the need for using a bioretention mix as opposed to the native soils.

The devastation caused by Hurricane Sandy brought forth an urgent need to reassess the flood protection measures for buildings and infrastructures in the north east region and in particular metropolitan area of NYC. To develop more resilient infrastructure and to account for changes in climate, FEMA increased the design flood elevation (DFE) requirements for buildings in New York and New Jersey. Designing for an increased flood elevation necessitates geotechnical engineers to consider the impact of the uplift/buoyancy forces generated under any building foundation slab particularly those buildings which are designed to have water tight basements. This paper describes a new field investigation method in conjunction with numerical analysis study conducted for the multi-story residential buildings located in Red Hook area of Brooklyn, New York. Scope of this study included analyzing impact of the floods on building foundations and developing remedial design solutions to mitigate the impact.

Accurate analysis of water retention curves (WRCs) for industrial and mining residuals such as chromium ore processing residue (COPR) is required to predict the unsaturated transport of hazardous contaminants (e.g., hexavalent chromium) in the vadose zone as well as to assess the performance of cover systems. In this study, unsaturated properties of unweathered gray-black (GB) and weathered hard-brown (HB) COPRs were determined for transport simulation based on the results of unsaturated soil testing including hanging column, pressure plate, and chilled mirror hygrometer tests. In addition, the water-retention characteristics were evaluated via the van Genuchten, Brooks-Corey, and Fredlund-Xing models. GB COPR exhibits a bimodal WRC due to hydration occurring during testing while HB COPR has characteristics similar to fine material. The chemical and mineralogical compounds of GB COPR were changed as a result of this hydration and influenced the model parameters.

A road is often built with soils compacted at their optimum water contents to achieve the best performance. Soils are sensitive to small water content variations and the ambient environment controls the soil water migration after construction. The soil-atmosphere interaction is a dynamic process under the influence of ambient climatic conditions, such as wind speed, solar radiation, precipitation, air temperature, relative humidity, vegetation evapotranspiration. The complexity of the problem makes it very difficult to reasonably evaluate the roadway long-term performance. This paper aims at evaluating the soil moisture variations within a pavement structure under the influence of ambient atmosphere. A hydro-mechanical-climatic model for saturated and unsaturated soils was first proposed. The climatic data are readily available from a local weather station to establish the flux boundary conditions for numerical simulation. Half of a two lane road was simulated to evaluate the moisture migrations within the pavement structure. Simulation results showed that the proposed model able to evaluate the dynamic soil moisture migration under the influence of ambient climatic changes.

Calcium-based stabilizers, such as lime, is often used for stabilization of cohesive subgrade soils to enhance its mechanical properties. However, its hydraulic properties which are presumed to be significantly affected may only be evaluated in the saturated state. In reality, the hydraulic structure may be in unsaturated condition during most of the year in hot and arid climatic regions having low water level on the upstream side of the hydraulic structure. In this research, an expansive soil from a levee in North Texas which is prone to slope stability issues was considered for stabilization using lime and the variation of hydraulic conductivity with suction was studied for both untreated and treated soils using suction-controlled permeability tests. A modified triaxial apparatus was used to control the suction and apply a hydraulic head to measure the values of permeability during drying cycle. Results show that lime decreases both saturated and unsaturated permeability of soil significantly.

Soil thermal conductivity is a function of pore water saturation, temperature, and stress level. A suction-controlled thermo-mechanical (SCTM) method has been developed to measure thermal conductivity of unsaturated soils at different temperatures (5.5°C to 75.5°C), isotropic normal stresses (35 kPa to 400 kPa), and wetting conditions. The apparatus consists of three main testing systems, including temperature-control, pressure-control, and sensor and data acquisition systems. This method permits quantification of soil thermal conductivity under the influence of stress level and temperature (i.e. construction and environmental conditions). A poorly-graded sand is used to investigate the effects of temperature and stress level on thermal conductivity of unsaturated sands. The thermal conductivity increases appreciably as stress and temperature increases at intermediate saturations (S~0.3 to 0.75). Maximum thermal conductivity occurs at 75.5°C and 400 kPa when S=0.54, where the value of thermal conductivity is about twice that at 5.5°C and 35 kPa. Hysteresis in thermal conductivity with respect to wetting-drying and loading-unloading was also observed.

Soil moisture, suction, and thermal conductivity are three essential soil properties to understand the behaviors of unsaturated soils. This paper presents the measurement of thermal conductivity dryout curve (TCDC) and soil-water characteristic curve (SWCC) for sands using a modified hanging column device (MHCD). The device was equipped with a newly designed thermo-TDR sensor, and a KD2 Pro (TR-1) sensor, and a METER group T5x tensiometer. Two saturated sand samples were prepared in the MHCD and underwent drainage and evaporation until dry. In the drying process, moisture content, thermal conductivity, and matric suction were continuously monitored using the installed sensors. The obtained results show that the MHCD device can provide an accurate measurement of TCDCs and SWCCs for sands.

Natural soil formation processes involve variable particle size distributions from one location to another, giving rise to an array of soils that transition from one general soil type to another within essentially similar deposits. Characterization of transition soils is something past research overlooked. Evaluation of the unsaturated strength behavior of a transition soil is carried out on mid-Atlantic-native silty sand that was used as backfill material in the construction of section 3 of the U.S. 301. In this work, a suite of suction controlled unsaturated consolidated drained triaxial shear tests are performed and the stress-strain characteristics of the transition silty-sand under different suctions are investigated. It is observed that the shear strength of the tested soil increased 2.5 times when suction changed from 100 kPa to 400 kPa.

Tsunamis are one of the most destructive naturally occurring phenomena that significantly affect shoreline morphology, often resulting in deep-seated erosional features and scarps. This study investigates the seabed response of sediments in the coastal nearshore, with particular focus on the influence of subsurface hydrodynamics and air entrainment in the intertidal zone that lead to sediment instability and momentary liquefaction. Entrainment of air bubbles due to tidal fluctuations increases the bulk compressibility of pore fluid and dampens the mechanical development of excess pore water pressure due to total stresses imparted by the weight of the wave. This pore pressure response differs from fully-saturated sediments overlain by intertidal sands at shallower depths and instigates seepage at the interface of these two layers and at the seabed surface. A fully-coupled flow deformation finite element analysis was performed in PLAXIS 2D to evaluate the pore water pressure response and seepage through a saturated sand layer overlain by a quasi-saturated (intertidal) sand layer during a hypothetical tsunami event. Results of the fully-coupled flow-deformation analysis illustrates the temporal and spatial development of excess pore water pressures and hydraulic gradients that arise at depth throughout the event. Computed results illustrate that the presence of a shallow quasi-saturated layer may lead to greater instability than a continuous layer of fully-saturated sediments.

The detrimental effects of moisture on roadway performance are well-known, thus drainage is crucial to roadway performance. Open-graded aggregates or non-wicking geotextiles are often used as drainage layers in a roadway system. These drainage layers rely on hydraulic gradient to remove water and are only effective under a high degree of saturation. Partially saturated soil can still contain too much moisture and be problematic to roadway performance. An innovative geotextile, the wicking geotextile, contains deep-grooved wicking fibers that can generate suction hence enable the wicking geotextile to remove moisture from unsaturated geomaterials. To verify the unsaturated drainage effect of the wicking geotextile on the mechanical behavior of a road section, three large-scale cyclic plate loading tests were conducted in this study. Each test was comprised of a 0.3 m thick base course over a 0.9 m thick subgrade. The three sections included a control section, a non-wicking geotextile-stabilized section, and a wicking geotextile-stabilized section. Geotextiles were installed at the base course-subgrade interface. Each section first underwent a rainfall simulation and then a 6-day drainage period. Cyclic plate loading tests were conducted at the end of the drainage period. The amounts of water distributed over and exited from the section during and after the rainfall simulation were recorded. The permanent deformations of the cyclic plate loading tests were measured to evaluate the performance of the roadway section. The test results show that the wicking geotextile provided fast drainage in the base layer and improved the performance of the roadway section in the cyclic plate loading test significantly.

In this paper, a state-dependent, bounding surface plasticity model for simulation of the behavior of unsaturated granular soils is presented. The model is an extension of an existing critical state compatible, hyperelastic model for saturated granular soils. The hyperelastic nature of the model, in which elastic strains are obtained from free energy functions, satisfies the conservation of energy (first law of thermodynamics). Compatible with the mechanics of unsaturated soils, the model has a zero initial pure elastic region. To create an appropriate hydro-mechanical coupling, a new generation of Bishop’s effective stress theory is used in conjunction with a soil-water characteristic curve. With a given set of parameter values, the proposed model captures the main features of shear and volumetric behavior of unsaturated granular soils over wide ranges of matric suction, density, and net confining pressure.

Natural and man-made unsaturated soil slopes can be subjected to different temperatures due to soil-atmospheric interaction, thermally-active earthen systems, and human-induced activities. Such nonisothermal conditions can affect the stress state variables, leading to changes in the soil strength and stability of slope. The main objective of this study is to investigate the stability of unsaturated soil slopes under elevated temperatures. For this purpose, Bishop’s effective stress expression for unsaturated soils is extended to account for the effect of temperature on matric suction and effective degree of saturation. The effective stress expression includes a nonisothermal soil water retention curve model to consider the thermal effects on the surface tension, soil-water contact angle, and adsorption by the enthalpy of immersion. The proposed effective stress model is then incorporated into an infinite slope stability analysis of a hypothetical silty soil under no-flow (hydrostatic) condition. The formulations are used to monitor matric suction, suction stress, and factor of safety of slope for different temperatures. The results suggest that the effects of temperature on slope stability can be significant. It was found that by increasing temperature from 25°C to 40°C and 60°C, the matric suction decreases by approximately 24% and 39%, suction stress increases by approximately 30% and 45%, and the FOS decreases approximately by 5% and 11%, respectively.

Constant water content (CW) triaxial tests were performed on unsaturated clayey sand to simulate undrained loading condition. The CW test is performed in which pore-air is allowed to drain while pore-water is kept undrained. Volume change mainly occurs due to drainage of pore-air during shearing. This study investigates the relationship between the change of matric suction during shearing and the initial matric suction prior to shearing. Results show that in general the matric suction decreases during shearing for the range of initial matric suction used in this study. The percent reduction of matric suction relative to the initial matric suction was approximately 40 to 50% and the value increases as the initial matric suction increases. The amount of reduction is related to the development of excess pore pressure and the degree of saturation at failure. Based on the results of this study, the analysis of unsaturated undrained shear strength based on the initial matric suction is not appropriate.