Geotechnical Frontiers 2017: Transportation Facilities, Structures, and Site Investigation

Densified aggregate piers have been widely used for ground improvement since the mid 1990s. The piers are typically constructed by backfilling cylindrical cavities with densified stone using a vertical ramming apparatus. The strength and compressibility of densified aggregate piers systems are confining stress dependent and tend to have low capacities in highly compressible soil because of their tendency to bulge into weak soil. This paper describes the design and construction of a densified aggregate pier system with polymeric shells for confinement in soft soil for a highway embankment in Seeley’s Bay, Ontario, Canada. The method allows for the insertion of high density polyethylene (HDPE) sleeves into the ground through the soft materials using a specially adapted mandrel. This paper is of particular significance because it presents significant insight into an effective ground improvement method in weak and sensitive soil subject to shear strength degradation by traditional aggregate pier methods.

A new grade separation for the Elgin O’Hare Expressway required a widening and grade increase for a 185-meter long embankment section carrying Illinois Route 53 across a series of peat bogs. The subsurface investigation showed a wetland developed over a kettle basin subsided into glacial diamicton and subsequently filled with lacustrine clay, silt and organic soils. The organic soil sequence included fibrous peat sandwiched between upper and lower layers of soft, organic-rich clay and silt. As an alternative to the costly dry-land bridge concept an alternative was proposed to place the new embankment over a 900 mm thick aggregate platform reinforced with two layers of biaxial geogrid and supported on 9- to 12-meter long timber piles. The timbers were driven 7-foot on-square center into competent glacial diamicton. The system was designed for 300 mm settlement at the top of pavement. Local excavation of the existing fill was required to achieve the critical height. High groundwater and soft ground resulted in challenging but manageable working platform conditions. Pile-driving analyzer tests confirmed capacity of timber piles and established site-specific driving criteria.

The I-295/I-76/Route 42 Direct Connection is a multi-phase, 9 year, $900+ million highway improvement project in Camden County, NJ. The New Jersey Department of Transportation (NJDOT) specified a design-build column supported embankment system (CSES) to control settlement and accelerate construction of several mechanically stabilized earth (MSE) wall embankments. This paper discusses methods for designing controlled modulus column rigid inclusion support across varied soil conditions and MSE wall embankment configurations. Additionally, results of initial CSES settlement predictions are compared with measured values from the geotechnical monitoring program across Contract 1 CSES work areas.

A numerical study using the finite element method was performed with the purpose of examining the lateral load response of rigid inclusion-supported footings. The lateral load behavior of rigid inclusion-supported footings is currently poorly understood. Uncertainty exists in regards to the performance of these systems under lateral loading. The results of the numerical study confirm earlier findings that show that the load transfer platform, a bridging granular mattress and one of the main components of a rigid inclusion-supported footing system, plays an important role in determining the capacity and response of such systems to lateral loading.

Predicting the response of soil profiles during earthquakes is one of the major challenges in geotechnical earthquake engineering. The presence of reinforcing elements such as stiff columns adds further complexity to the problem due to the interaction of these stiff elements with the surrounding ground. This research presents the results of advanced numerical simulations of dynamic centrifuge tests performed on a columnar reinforced model with a loose sandy profile. The model was subjected to earthquake base motions of varying intensities to investigate the reinforcing mechanisms of soil-cement columns. Numerical simulations were performed using the finite element computational platform OpenSees with pressure dependent multi yield (PDMY02) constitutive model. Simulated and measured values were compared for seismic intensity, excess pore water pressure and ground settlement at different locations within soil profile. The calibrated numerical model was able to realistically predict the response of reinforced ground.

The modern approach to the piled embankment includes the basal reinforcement of geosynthetic layers. Current design guidelines for piled embankment in the Netherlands, Germany, and U.K. have been updated to accurately estimate the practical tensile strains of employed geosynthetics, whereas the analytical approaches were usually underestimated against the experiment and in-situ results. In this study, a series of finite element simulations concerning different types of soil-geosynthetics interaction were conducted to reveal the difference of frictional modeling method. The geosynthetic strains along the diagonal and orthogonal direction from the pile center toward to the other pile were obtained according to the loading condition. The completely different responses were observed with respect to the type of the frictional model.

Continuous compaction control (CCC) systems utilize a mounted accelerometer, GPS unit, and data acquisition system on soil or asphalt compaction equipment, in order to collect data about the compaction process in real time and over 100% of the compaction evaluation area. During their use, CCC systems may collect anomalous data that can have an influence on reported compaction quality results, and which can lead to erroneous conclusions about the degree of compaction of the soil, or inappropriate regression models between CCC data and in situ measurement data. In the current study, an existing neighboring weighted-estimation method was applied to the results from a field study in which a variety of CCC and in situ test data had been collected, to quantify and filter out anomalous data. Other researchers have proposed that this approach can improve presented CCC data, resulting in improved regression relationships between CCC data and in situ measurement data. For the data set that was evaluated, the results indicate that the removal of anomalous data using this methodology did not yield a significant change in the relationships between the CCC and in situ test results.

The Dominion Cove Point LNG Terminal, located in Lusby, Maryland, recently began a $3.8 billion-dollar terminal upgrade to expand capacity and facilitate export capabilities. Given the soil conditions, strict vibration thresholds, and site logistics at the active LNG facility, Dominion and the IHI-Kiewit Cove Point JV selected drilled, cast-in-place elements as the primary foundation type to support temporary/permanent structures. Over 4,750 Auger cast-in-place piles and 700 drilled shafts were installed. Due to the sensitivity of the proposed structures, extensive non-destructive integrity testing (NDT) was required. The initial quality control program included pile echo testing and cross-hole sonic logging (CSL). However, due to site specific limitations, alternative NDT methods were required. Thermal integrity profiling was ultimately selected and the results of large-scale testing highlight this new technology as a highly effective and cost-efficient method of testing drilled, cast-in-place foundations.

Intelligent compaction (IC) is an emerging technology for compaction quality control of embankment, base and hot mix asphalt layers. A number of roller manufacturers have implemented the IC technology in their compaction equipment. Each of these systems employs different instrumentation to collect vibration data and uses different algorithms to estimate the stiffness of the compacted layer. Variability of the IC data has significant impact on the compaction quality management process. To evaluate the sources of variability, a study was performed on a section of a highway during compaction of earthwork and subgrade layers. The IC data were collected during pre-mapping of the existing embankment layer and mapping of the compacted subgrade layer. The geospatial variation of the IC data was evaluated at different construction stages. A number of modulus-based nondestructive spot tests were also performed to investigate any possible correlation with the IC data. Soil samples were also extracted at different spots for laboratory moisture content estimation. The results of the analysis showed that the geospatial variability of collected data, data reduction algorithm and accuracy of global positioning system affects the variability of collected IC data.

Noise and vibration are critical issues associated with pile driving operations in an urban environment. Alternative foundations such as drilled shafts and augercast piles alleviate much of the operational noise and vibration. However, the cast-in place installation process may raise concerns in quality control if not adequately monitored. Post grouting the drilled shaft base has been widely used to mobilize a larger portion of the tip resistance prior to construction of the superstructure, thereby controlling the axial displacement during the service. In response to the operational challenges in urban environments, the Florida Department of Transportation and the University of Florida have recently developed a new generation of deep foundation, namely “jetted and grouted precast pile”. The process consists of pressurized water jetting a concrete pile instead of a hammer-driven installation, and subsequent side and tip grouting the pile, which significantly improve skin and tip resistance, respectively, as well as lateral and torsional stiffness. Several studies have been focused on such increase in axial and torsional resistance by grouting techniques. However, there has been little field data available to support quantifiable noise and vibration reduction by jetting and grouting processes. This paper presents field measurements of noise and ground surface vibration during full-scale installation of jetted and grouted piles. Comparison of measured data to recommended noise and vibration limits suggests that jetting and grouting techniques are a viable solution for urban geo-infrastructure development.

Mechanically stabilized earth (MSE) walls are widely used earth retention systems. MSE walls often contain galvanized steel strips as mechanical reinforcement between layers of specified backfill material. Inclusion of these strips creates a stronger composite material connected to a visually appealing wall facing; however, galvanized steel reinforcement is potentially vulnerable to corrosion. Corrosivity of MSE backfill may be characterized using electrical resistivity. Many designers currently use variations of the American Association of State Highway and Transportation Officials (AASHTO) standard T 288 to calculate resistivities of MSE backfill and require a minimum resistivity value for metal-reinforced backfill, typically 30 to 50 ohm-meters. A new procedure has been developed that appears to more accurately simulate field conditions. Material resistivities determined using this Proposed ASTM were up to two orders of magnitude higher than those determined for the same select materials using T 288 and matched well with field tests conducted by Kansas State University on the same compacted aggregate backfill.

The chemically-stabilized subgrade (CSS) soil layer in a pavement structure can undergo flexural fatigue as a result of a high number of loading cycles and brittleness of the stabilized soil. The type and amount of chemical stabilizing agents are generally selected based on the results of unconfined compressive strength (UCS) and/or resilient modulus (M_r) tests. The UCS and M_r tests help characterize the compressive behavior of the soil and do not specifically assess the flexural behavior of the CSS layer under cyclic loads. This study aims to evaluate the fatigue life of the CSS layer and compare it with other common indicators such as UCS and M_r. For this purpose, a series of UCS, M_r and four-point flexural fatigue (FPFF) tests were conducted on CSS soil samples. The materials tested in this study consisted of six blends of a lean clay stabilized using cement kiln dust (CKD) and hydrated lime. The CKD was mixed with the soil at 5, 10, and 15% by weight of dry soil. The hydrated lime was mixed with soil at 3, 6, and 9% by weight of dry soil. It was found that while increasing the amount of stabilizing agent resulted in higher UCS and M_r values, it had an adverse effect on the fatigue life of CSS. The specimens containing 5% CKD and 3% lime showed the highest fatigue lives compared with other mixes. It was concluded that the strain endured by the material at the peak load (strain at failure) plays an important role in the fatigue life of the CSS. CSS samples with a high strain level at failure possessed a high fatigue life while those with a lower strain at failure failed after a relatively low number of loading cycles.

South Carolina recently experienced a 1000-year rainfall event that caused catastrophic flooding and crippled the transportation infrastructure. Initially, almost 400 roadways were closed due to flooding, a majority of which were closed from roadway washouts. Many of these roadway washouts resulted from failure of the pipe culvert soil system beneath the roadway. The culvert infrastructure is critical to not only preventing flooding during normal and extreme conditions but is integral to proper road and highway maintenance. This paper presents the results from a post-flood reconnaissance study aimed to collect perishable data from sites where pipe culverts failed and roadways were washed out. The study included collection of extensive photographic evidence and documentation of descriptive information related to the failure; collection of soil samples; and field and laboratory geotechnical tests.

In the past decade, the biofuel industry has seen significant development in the United States and all over the world. Based on a review of recent bioenergy literature, it appears the by-products derived during biofuel production may play a positive role in value-added engineering applications. Recent studies at Iowa State University (ISU) demonstrated the successful utilization of biofuel co-products (BCPs) in pavement subgrade stabilization. This paper discusses the effect of three types of BCPs containing different lignin content from lignocellulosic biorefineries on a typical Iowa soil called loess in terms of freeze and thaw durability. Emphasis is given to detailed data analysis of laboratory test results in comparing three types of BCPs treated soils with untreated and cement treated soils. Results reveal that the BCPs investigated in this study are promising materials to improve freeze and thaw durability of the Iowa loess classified as CL-ML or A-4 for geotechnical applications.

Permeability and diffusivity function of expansive subgrade soils are critical parameters in the design of pavements. They govern the moisture flow in and out of the soil and thus the amount of movement the subgrade experiences. Several models have been proposed to estimate the both functions from the soil water characteristic curve (SWCC) and the saturated coefficient of permeability. However, these methods reveal a noticeable difference in the determination of both functions. The permeability coefficient can also be measured from the diffusion coefficient and the slope of the SWCC, or experimentally by the instantaneous profile method. In this paper, a comparison study in the determination of both parameters from the most frequently used SWCC models, diffusivity test, and instantaneous profile method is carried out. It is found that SWCC models reveal significantly less measurements than those derived from the other two methods. However, the results from the diffusivity test manifest good agreement with those derived from the instantaneous profile method.

The goal of this study is to examine the feasibility of using a bridge structural testing system and finite element modeling (FEM) to assess the impact of heavy hauls in terms of stresses and the corresponding reduction in service life for portland cement concrete (PCC) pavements on grade. FEM simulation results are compared for various numerical treatments of the subgrade using the programs EverFE and COMSOL. With the simplified dense liquid foundation subgrade treatment used in EverFE, the experimentally measured bending strain profile in the slab could not be accurately captured using a single coefficient of subgrade reaction. A more general optimized 3D solid subgrade model was developed in COMSOL using the pseudo-coupled method, by modeling a large solid soil domain surrounding the slab, with the subgrade modulus increasing from the center to the edge of the slab in three separate regions. The optimized 3D solid subgrade model resulted in better agreement with experimental strains.

Fine-grained soils are often problematic if they are used to construct certain types of earth structures or pavement foundation layers. If the use of poor site-specific fine-grained soils is desired for cost reasons, it can be useful to perform chemical stabilization to improve their engineering properties. Calcium carbide residue (CCR) is a by-product of the acetylene production process, which can be used as a cost effective and sustainable cementing agent for soils. This paper examines the effects of CCR content and curing times on the engineering characteristics of CCR stabilized fine-grained soils. In this study, a green bentonite (having a predominantly montmorillonite mineralogy) and white kaolin (having a predominantly kaolinite mineralogy) were used as representative clay minerals that needed stabilization. Compaction, unconfined compression strength (UCS), and direct shear tests were performed to assess the engineering properties of the stabilized clay soils. From the test results, it was observed that in both clays the optimum water content tended to increase and the maximum dry density tended to decrease as the CCR content increased. The UCS test results showed that 9% and 12% CCR contents yielded optimal strength gain for the montmorillonitic and kaolinitic clays, respectively. The direct shear test results also showed significant gains in cohesion and friction angle for both soils at their optimum stabilization levels.

Soil-bentonite slurry trench cutoff walls are widely used for seepage control, levee repair, and pollutant containment. Their widespread use in these critical applications requires a better understanding of their as-built condition and long-term behavior. The in situ hydraulic conductivity of soil-bentonite cutoff walls is stress dependent. Changes in hydraulic conductivity of the wall over time can result from changes in stress due to consolidation and load transfer though shear to the formation along the sidewalls of the trench. This paper describes a soil-bentonite cutoff wall designed, constructed, and instrumented for the principal purpose of research. The cutoff wall instrumentation is designed to monitor the in situ conditions in the backfill in three dimensions (transverse, longitudinal and vertical), vertical and lateral deformations, and pore water pressures. All data is being collected as a function of time and location within the wall.

Electro osmotic (EO) ground improvement technique has a promising performance history in improving the properties of fine-grained soils. A review of data from 11 case histories indicates that EO consolidation can strengthen various types of fine-grained soils, from slurries to clayey silt, with initial shear strengths from 1 to 28 kPa. The level of shear strength improvement depends on the ratio of applied electrical potential difference and electrode spacing (V/S). A maximum induced shear strength of up to about 4 times of initial value has been observed with 0.18 < V/S < 0.25 in about 4 days. A maximum improvement depth of 1.4 times the electrode length has been reported. In addition, utilizing electrodes made up of thin metal core, preferably steel covered by electrically conductive geosynthetics, can minimize gas production and potential loss at electrode-soil interfaces and consequently decrease the level of power consumption in EO systems.

Stone columns are an economic solution for improving the bearing capacity of shallow foundations on soft soils. A novel impulse load test was developed and used to quantify the load-displacement response of shallow foundations on stone columns at a clay site. The testing methodology used is the rapid plate load tester. Static and dynamic tests were conducted on a 2 m x 2 m footing supported on slightly overconsolidated clay reinforced with stone columns and the results are presented. The stone columns were 6 m deep and constructed using the dry method at different area replacement ratios by varying the spacing and diameter of the stone columns. Static and dynamic field tests were performed to target loads of 2000 kN and equivalent bearing pressures of 500 kPa. Displacement time histories were acquired by both photocells and accelerometers. The unloading point method was used to derive an equivalent static load settlement curve for the footing on clay soil both prior as well as post improvement. The derived static curves show good correlation with measured load settlement curves in the static mode.

Treatment method can have a significant influence on the mineralogy of the precipitated calcium carbonate (CaCO₃) in soil treated by microbially-induced carbonate precipitation (MICP). Rhombohedral calcite crystals are the most desirable form of CaCO₃ for geotechnical applications due to their thermodynamically stable nature. However, not all treatment methods produce this form of CaCO₃. Soaking and injection are two methods for MICP treatment of soil commonly used in the laboratory. The injection method was found to be more efficient for obtaining rhombohedral calcite crystals. It appears that rhombohedral calcite crystal growth is hindered in the soaking treatment method due to high concentration of organic matter in the treatment solution. These results indicate that mineralogical considerations should be included when determining an appropriate method for MICP-treatment of soil in the laboratory such that the resulting specimen is representative of the in situ mechanical behavior of MICP-treated soil.

Soil arching is major factor that often controls the response of box culverts to static loads. The effect of relative stiffness between the culvert and the surrounding soil is critical in considering the complex soil-culvert interaction (SCI). In practice, box culverts can have different characteristic length scales in relation to vertical and horizontal soil stress changes. Therefore, the effect of box culvert size was investigated experimentally and numerically. In the present study, centrifuge tests were conducted to investigate the SCI considering the height of soil column and culvert geometry. The results were used to calibrate a numerical model to further investigate the response of the box culverts to static loads. The results have been evaluated for bending moment, soil pressure and soil culvert interaction factors. These results were then used to establish charts that may be employed to assess design values for box culverts.

Seismic response of shallow buried box tunnels with geofoam side cushions was investigated through finite difference analyses with a numerical model that was validated against published experimental results from centrifuge tests. Analyses were carried out to investigate the effects of embedment depth, geofoam cushion properties and seismic excitation characteristics. Wall deformations as well as lateral dynamic earth pressures at various points on the embedded structures were monitored in the numerical analyses. Results were compared to those of a deformation based analytical approach. The study demonstrates that installation of EPS geofoam cushions may result in a reduction of the seismic earth force and sectional forces on the tunnel structure compared to the case of a structure without geofoam cushions. Structural rigidity of the embedded structure and embedment depth, as well as thickness ratio of the geofoam cushion, play an important role in the reduction of seismic earth forces and racking deformations.

This paper presents findings from a critical review and an analytical study of soil stiffness values for the load rating of reinforced concrete box culverts. The responses of the soil-culvert system under dead and live loads were examined separately for a production-simplified, two-dimensional, linear elastic, soil-structure interaction model. First, soil-culvert systems were analyzed to determine dead-load-induced moments in the structure. The results were compared with moments obtained from an AASHTO policy-based structural-frame model and a calibrated value of static soil modulus, E = 10 ksi was selected as the optimum. A comprehensive literature review evaluated reasonable soil stiffnesses for live load analysis in culvert load rating. Typical resilient moduli of 12, 24 and 36 ksi for low, medium and high-quality culvert backfill soils were identified for live load predictions in the soil-structure interaction model.

The average vertical pressure on a buried structure can be calculated using the silo theory, which assumes the translation of a vertical prism of soil above the structure that is resisted by friction on the sides of the prism. One of the key assumptions made is the value of the coefficient of lateral stress, K. In this study, an assumption regarding the rotation of principal stresses in the yielding soil has been used to calculate the average coefficient of lateral stress acting at the side of a prism of yielding soil above the horizontal buried structure. The calculated value using the proposed method agrees well with experimental observation made in literature for the value of K, and is suggested for use in the estimation of loads on buried structures, where it is expected that the structure will yield relative to a stiff body of soil.

This parametric analysis illustrates the relative influence of six parameters on reinforced concrete box culvert (RCBC) load rating using a production-simplified soil-structure interaction demand model. Frequently, field inspections show in-service RCBCs to perform adequately, but load rating per AASHTO guidance requires load posting. Parameters such as (1) the culvert design, (2) cover soil depth, and (3) soil stiffness are driven by the in-service culvert condition. The test matrix consists of three RCBC designs evaluated under three cover soil depths embedded in three soil stiffnesses. Load raters may implement less conservative, more accurate assumptions for (4) pavement stiffness, (5) effective moment of inertia, and (6) the top interior wall fixity, as appropriate. Cover soil depth and design showed significant impact on the culvert load rating, but are defined by the culvert condition. Less conservative assumptions for the effective moment of inertia had the greatest impact on the load rating, followed by the inclusion of pavement stiffness.

A complex soil-structure interaction is involved when buried flexible plastic pipe or storm chamber systems are placed under load, and the stability of these buried systems must be demonstrated under “worst-case” live and/or dead load conditions. While it has become common place to demonstrate buried structure stability through analytical methods, including empirical equations or finite element modeling, full-scale burial tests have been recognized as necessary to, at least, calibrate these analytical methods. Two types of field tests have been used for this purpose: conventional excavation/backfill construction and compact burial chambers. This paper describes these full-scale burial testing facilities and procedures and how they have been used to develop deflection and strain data, along with a visual record, for use in correlating results of small-scale laboratory tests and calibrating design models. Included is an example of each type of field test – one evaluating storm chambers and another looking at corrugated pipe.

The mechanistic-empirical pavement design guidelines (MEPDG) recommend use of material modulus in lieu of structural number for pavement base layer thickness design. In this study a methodology was developed to determine a single effective modulus for a base layer using laboratory nonlinear modulus characterization data and a nonlinear finite element response model. With this model, a single representative modulus can be determined by a back calculation procedure in which pavement surface deflections from a nonlinear analysis are matched via an equivalent linear analysis. An equivalent linear analysis using effective moduli for both an unbound base and the subgrade can predict the structural response of an asphalt surface layer in a flexible pavement. It should be possible to utilize these structural response predictions in the assessment of cracking performance of the surface layer. However, caution is warranted in predicting the structural response of the unbound base and subgrade layers using an equivalent linear analysis. Use of an effective modulus for a nonlinear base layer appears reasonable for very thick pavement structures, but appears to under predict vertical strain at the top of subgrade.

Concerns about ever-increasing construction costs coupled with the negative impacts on the environment have led the asphalt industry to search for alternatives that can potentially mitigate these effects. One type of technology that addresses both production cost and environmental issues is the warm mix asphalt (WMA). It allows for mixing, production, placing, and compaction of asphalt mixtures at significantly lower temperatures than conventional hot mix asphalt (HMA). The goal of this study is to compare the laboratory moisture susceptibility and permanent deformation performance of HMA and WMA mixtures. Further, to ascertain early field performance of HMA and WMA. Six field rehabilitation projects across Louisiana were selected for the evaluation of WMA technologies. Several chemical additives and processes were evaluated. A total of 18 mixtures were included in this study. The field experiment included three types of WMA technologies, chemical additives (Evotherm and Rediset), organic (Sasobit), and foaming processes (astec double barrel green system and accu-shear system), two mixture compaction levels (design traffic levels 1 and 2), two asphalt binder types (PG70-22M and PG76-22M per Louisiana Department of Transportation and Development (DOTD) specifications), two projects where higher reclaimed asphalt pavement (RAP) contents were evaluated; and two nominal maximum aggregate sizes (12.5 mm [1/2 in] and 19.0 mm [3/4 inch]). The results of this study showed comparable performance of conventional HMA and WMA in terms of moisture sensitivity tests. The modified lottman and loaded wheel tracking (LWT) tests had, in general, good agreement for mixture evaluation in terms of moisture sensitivity and field performance results. The field performance confirmed the prediction of the moisture sensitivity tests, modified Lottman and the LWT.

The objectives of this research were to model and incorporate the uncertainty in pavement material properties for mechanistic empirical (ME) analysis. The uncertainty in aggregate gradation and volumetric properties in superpave mixture design was considered for hot mix asphalt (HMA). The uncertainty in the properties of the granular materials was modeled in terms of the uncertainties in resilient modulus and degree of saturation using thornthwaite moisture index (TMI) and climatic database. The distributions of HMA dynamic modulus and resilient modulus of granular materials were determined from the distributions of the constituent random variables. Reliability analysis was performed using different allowable cracking. The research concluded that TMI can be used to model the uncertainties in climatic factors and response surface method can be used to incorporate material uncertainties in pavement analysis. The reliability curves developed in the study can be used to determine pavement thickness for a given reliability.

Mechanistic methods are introduced to provide a realistic prediction of the performance of asphalt pavements. Despite the advantage of these methods in providing accurate and advanced material characterization, they should take into account the uncertainties associated with material properties and models. Such material properties include the linear viscoelastic response functions that characterizes the behavior of asphalt concrete such as relaxation modulus E(t). Typically, complex modulus E* data is obtained by lab testing and then used to determine E(t) through mathematical interconversion methods. The objective of this study is to propagate the inherent variability in E* data for various reduced times into E(t). This was achieved by analyzing the data of E* testing and interconverted E(t) from three different mixes that include at least eight replicates with a probabilistic framework that allows for a preliminary quantification of uncertainty. Monte Carlo simulations were used to propagate the uncertainties of the Prony series coefficients to determine the mean, coefficient of variation (COV), and probability distribution in E(t) as a function of reduced time.

Fracture of asphalt mixtures was modeled using a heterogeneous 2D-discrete element method simulating the semi-circular bending (SCB) test. The 2D internal structure was generated virtually utilizing 2D images of aggregate particles. The internal structure was produced to match specific mixes gradation, namely: superpave, porous friction course, and coarse matrix high binder mixes. The variability of SCB testing results was studied by producing 50 virtual cases for each of the mixes. In addition to randomly selecting the location of the aggregates within the internal structure, the location of air-voids was also random. The results indicated that the location of the aggregates and air-voids has a strong influence on the crack initiation, propagation and the crack path. Analysis of SCB fracture behavior for aggregates from different sources with different strength and shape properties indicated that the aggregate source plays a role in the variability, but none of the strength-shape combinations led to a significantly lower variability.

The accuracy of the reliability-based designs for pavements mostly depends on the probability density functions (PDF) associated with the resilient modulus of the pavement layer. The present study attempts to find out the appropriate PDF corresponding to the base resilient modulus (Mr) of different virgin aggregates that are used in the flexible pavements. Extensive literature study has been conducted and about 120 data points were collected from various global studies performed on virgin aggregate base materials for their use in flexible pavements. Histogram and statistical analyses are performed on the dataset. An accurate PDF is then proposed from the available distributions by using percentile (P-P) and quantile (Q-Q) fit assessment plots. The proposed mean, standard deviation and coefficient of variation associated with the best PDF are further useful for developing the reliability based design optimization methods for pavements.

Ladle furnace slag (LFS) is a solid waste by-product from the secondary stage of steel making process in ladle refining furnace. An extensive suite of engineering and geotechnical tests was undertaken on LFS aggregates to evaluate its potential to use as a road construction material. The chemical composition and microstructure of LFS samples were evaluated using X-ray fluorescence analysis (XRF) and scanning electron microscopy (SEM). The effect of different curing regimes on the strength of unbound LFS was also investigated. It was found that both duration and temperature of the curing had a vital role in the strength development of LFS samples, which could be attributed to the relatively high lime content of the LFS material. The suitable engineering properties of LFS materials could make it a reliable substitute for quarry produced pavement materials, which may result in diverting large amount of LFS from landfills.

The object of this study was to investigate the impacts of municipal solid waste incineration (MSWI) bottom ash (BA) regarding cement hydration and leaching when used cement-based materials. As a mean of cement hydration assessment, energy dispersive X-ray (EDS) and X-ray diffraction (XRD) analysis were conducted on MSWI BA ‘as is’, hydrated BA, and BA-combined cement paste. The results show that MSWI BA led to small amount of cement hydration. In addition, the leaching characteristics of major alkaline and trace elements from concrete containing varied amounts (10%-50%) of BA were investigated by synthetic precipitation leaching procedure (SPLP) batch testing. The results reveal that the release of highly alkaline elements increases with increasing the BA content. However, the release of selected alkaline and trace heavy metals is reduced when mixed with PCC properly due to the binding effect in cement mixtures and consuming from cement hydration. Results show that crushed PCC mixed with the MSWI BA demonstrated significant reduction of Al and Si. Moreover, Mg ranged from 475.9 μg/L for the 100% BA to 181.3 μg/L for the PCC with 50% BA and Cu ranged from 45.5 μg/L to 15.1 μg/L.

The premature cracking of asphalt concrete (AC) layers in flexible pavements is one of the major concerns of the pavement community. The overlay tester (OT) is considered by several highway agencies to evaluate the cracking resistance of AC mixes. The variability of OT results is expressed as a major concern in reliably characterizing the cracking potential of AC mixes. The main objective of this paper is to evaluate the variability of the number of cycles to failure (currently the main output parameter of OT test) and propose alternative parameters that can be measured for characterizing the cracking potential of AC mixes. Three AC mixes were used to evaluate the uncertainties associated with the performance of the OT tests. The OT can be employed with more certainty if cracking parameters measured from the first hysteresis loop and load reduction curves are implemented on a data interpretation method.

Viscoelastic material functions of warm-mix asphalt are not well defined yet for reasons like relatively newer technology in United States and also varies with different technologies. The rutting performances of warm-mix asphalt are also relatively new. This study evaluates the effects of different warm-mix agents on the viscoelastic material functions and rutting performance of asphalt concrete. A control hot-mix asphalt and three warm-mix asphalt mixtures were collected from manufacturing plant with identical aggregate type, size distribution, and binder grade. The loose asphalt-aggregate mixtures are compacted, cored and sawed to cylindrical specimens for dynamic modulus and rutting resistance testing. A numerical method is used to convert complex modulus function to relaxation modulus and creep compliance. In essence, the warm-mix asphalt with water-free chemical agent showed higher stiffness characteristics. However, the warm-mix asphalt with surfactant-based WMA technology is found to be superior in terms of rutting performance, whereas, the warm-mix asphalt with water-free chemical agent is found to be inferior.

The primary reason for limited use of reclaimed asphalt pavement (RAP) is the uncertainty of the long-term pavement performance. Understanding the response of virgin material and RAP material to oxidative aging is important to the selection of virgin and RAP binder. Five different percentages (0%, 15%, 25%, 35% and 40%) of RAP included asphalt concrete (AC) were designed to compare the effects of aging on hot mix asphalt (HMA). To assess the effect of aging on AC, the samples were subjected to oven aging following AASHTO R30 protocol. Successive aging the samples were conducted to quantify which RAP percentage is more susceptible to long-term aging. Dynamic modulus tests were conducted on control and aged AC samples. Results show aging of the material increases the complex modulus of all the samples irrespective of RAP percentages. The master curves indicates that as more RAP is added to the mixes, the curves shift upwards at the high frequency and a slight upward shift at the low frequency end of the curve.

This paper presents a study of the load-deformation behavior of geocell-stabilised subballast subjected to cyclic loads using a large-scale track process simulation apparatus and numerical modelling. The tests and numerical simulations were conducted to mimic the actual track conditions. Subjected to a given frequency and cyclic loads the predicted load-deformation behavior of the subballast with and without geocell inclusions match reasonably with those measured in the laboratory, and show that geocell could effectively decrease the lateral and axial deformations of the reinforced subballast. The results also provide an insight to design of rail tracks capturing the roles of geocell in decreasing lateral deformation of subballast. Additionally, the numerical modelling carried out in this study can be applied in the preliminary design of track substructure where a wide range of subballast aggregates and geocell mattresses with varying strengths and stiffness can be considered.

The performance of a flexible pavement depends, to a large extent, on the mechanical characteristics such as stiffness and deformation resistance of its base layer. The laboratory static triaxial compression tests are common to estimate these mechanical characteristics. The resilient modulus tests are the other laboratory tests that are also gaining popularity. These laboratory tests are usually augmented with field tests such as the plate load, lightweight deflectometer or dynamic cone penetration tests. Since the methods of compaction and testing are different, one can anticipate that the mechanical characteristics measured in the laboratory and in the field are different even at the same moisture content and density. In this paper, the relationships among the laboratory and field mechanical characteristics of a common base with different fines contents and moisture contents are evaluated, reported and discussed.

Unbound permeable aggregate base (UPAB), due to its relatively high porosity and permeability, is considered as an alternative to traditional impervious (e.g., dense-graded) bases for controlling subsurface drainage and pavement longevity in an economical and environment-friendly way. The UPAB layer is normally made of open-graded unbound aggregates and thus tends to suffer from insufficient structural strength (or stability). Aimed at further validating a new gradation concept for enhanced structural strength, this paper presented preliminary findings from a series of laboratory tests conducted to evaluate various gradation designs of UPAB materials in relation to mechanical stability. Five representative gradations were selected according to the current UPAB gradation band, and the effects of different UPAB gradation designs on the shear strength properties were investigated using a large-scale direct shear test device. Based on the experimental results, the optimum aggregate gradation design recommended by the new gradation concept for enhanced stability was consequently validated. The use of such optimal gradation is expected to achieve cost-effective UPAB design for long-life concrete pavements.

As horizontal construction extends into regions of the world with fewer technical resources, simple and compact technologies for remote soil assessment become necessary to reduce risk while increasing durability. To provide the capability to rapidly evaluate and improve soil materials for horizontal construction, a wash-based soil classification and engineering system, named the rapid soils analysis kit (RSAK), was developed. Physically, the wash based RSAK (W-RSAK) consists of a suite of scaled down laboratory soil test equipment packaged in a man portable case including software for predictive analysis. Processing 500 grams of soil material through the W-RSAK guided by an intuitive software user interface can be completed in 60 minutes by a single user. The resulting software output from the W-RSAK consists of a Unified Soil Classification, Atterberg limits, and prediction of the optimum moisture content and maximum dry density. It also includes the complete moisture-density curves at both standard and modified proctor compaction energy and the resultant soaked and unsoaked California Bearing Ratio curves to predict bearing capacity. The W-RSAK procedure was validated through a set of experiments on 14 varying soil types comparing classification and compaction to traditional laboratory and an earlier generation dry-based RSAK procedure. It was demonstrated that the W-RSAK procedure significantly improves classification estimations and is a potential solution to fill engineering gaps in soil design for contingency construction.

The use of recycled flex-base materials such as recycled crushed concrete aggregate (RCCA) and reclaimed asphalt pavement (RAP) are increasing considerably nowadays in pavement base layer applications. Increased use of these materials address the issues of depletion of natural resources and provide solution to the adverse effect on environment. The recycled materials utilized in this study was collected from the Texas Department of Transportation (TxDOT) approved sources. The properties of recycled base materials depend solely on the sources and their environmental aspects of using as base material needs to be analyzed. A comprehensive laboratory evaluation of geo-environmental properties of RCCA and RAP in untreated or cement treated condition were conducted in this study. The amount of RAP and RCCA varied from 0%-100% in the combination at 50% interval with cement content varying from 0% to 6% at 2% interval. The specimens were prepared at optimum moisture content and maximum dry density obtained from the test results. The geo-environmental tests included permeability and leaching tests. Leaching tests included pH, total and volatile dissolved solids, total and volatile suspended solids, turbidity and chemical oxygen demand (COD). Tests results were compared with the requirements of different environmental protection agencies. The comparison of tests results indicated that the recycled base materials were environmentally sound alternative to regular virgin aggregates and can be used in pavement base or sub-base layer.

Due to loading, granular materials forming the base of asphalt pavements experience crushing. After crushing, the fines produced in the granular materials move into their voids and causes an increase on the bearing capacity of the base. However, when the volume of the voids is decreased due to this fines migration, the hydraulic conductivity of the crushed material decreases. This change in the hydraulic conductivity of the material with time, may lead to failure of the pavement. Compression induced crushing and hydraulic conductivity tests were conducted on small gravels. In this study, the level of fragmentation of two kind of gravels (smooth and angular) was analyzed using fractal theory. The fractal dimension concept was used to evaluate the level of fragmentation of the gravels and it was correlated with their hydraulic conductivity values. The level of crushing in the gravels was also visualized using DEM.

Recently, automatic ballast sampling (ABS) methods have been introduced to the railroad industry to obtain a sample of ballast and underlying layers. Currently, manual-visual classification methods are used by experts to identify fouling conditions and degradation trends in the collected ballast samples. This paper presents an innovative approach developed for objective classification of ballast degradation using the combination of machine vision and machine learning techniques. Initially, various computer vision algorithms were used to generate features associated with images of ballast cross sections at different degradation levels. Next, the generated features were used alongside a visual classification database provided by experts to develop, train, validate, and test a feed forward artificial neural network (ANN) using a supervised learning method. This work was further extended by implementing convolutional neural networks (CNNs) to serve as automatic feature generators. The findings of this study showed that the proposed CNNs with an optimized topology could successfully classify ballast fouling in an effective and repeatable fashion with reasonable error levels. Further improvement of this technology holds the potential to provide a tool for consistent and automated ballast inspection and life cycle analysis intended to improve the safety and network reliability of U.S. railroad transportation system.

Hot mix asphalt (HMA) overlays are the most common and cost effective rehabilitation technique available to restore the serviceability of existing distressed pavement surfaces. It is often observed that within a short span of placing HMA overlays, the distress in the existing pavement surface reflect to the new overlay surface and this process is termed as reflective cracking. To reduce the effect of reflection cracks and to improve the performance of HMA overlays, the geosynthetic interlayers are placed at the interface of old and new pavement layers. The current study aims to understand the interfacial shear properties of geosynthetic interlayered HMA overlays placed on a distressed pavement surface. The interfacial shear properties are determined in the laboratory using a large scale interface shear test apparatus. The geosynthetic interlayers used in the current study are biaxial geogrids with varying material properties and aperture sizes and a geo-jute mat. The results indicate a reduction in the interfacial bond strength (shear) between the old and new pavement layers with the inclusion of geosynthetic interlayers at the interface zone. Among different types of geosynthetic interlayers used, the polymer modified polyester grid has shown least reduction (17%) in the interface bond strength. The maximum reduction of 46% in the interface bond strength was observed in the geo-jute mat interlayers.

A pilot study was performed to determine the viability of a permanently installed sinkhole detection device for use in both commercial and residential applications. The current state of the practice methods for sinkhole detection provide only a single snapshot in time of subsurface conditions. The theory investigated was the concept that if a sinkhole is forming underneath an existing structure, the void forming could be detected mechanically by a falling weight causing a trigger to alert occupants. The device would be installed through the existing floor and at a depth such that the sinkhole void could be detected prior to any damage to the structure. Prototypes were constructed and tested in various environmental conditions for durability and in simulated sinkhole conditions in the field. While impediments to widespread use exist, the device appears capable of serving as a sinkhole early detection system.

Sinkholes are one of the most frequent hydrogeological hazards in the Central Florida region. The risks related to sinkholes pose a significant threat to humans, infrastructure, and natural resources. It is important to identify the sinkhole-prone areas in order to mitigate or prevent damage and losses caused by sinkholes. The main objective of this study is to develop sinkhole hazard mapping for Central Florida region with a GIS technique. A sinkhole hazard map was generated by using frequency ratio (FR) model that analyzes the relationship between the sinkhole occurrence and sinkhole-affecting factors. Various hydrogeological factors that potentially contribute to the sinkhole formation in the region were identified and used for the analysis. The sinkhole hazard index (SHI) values for the entire study area were determined using the developed hazard model, and then used to produce the sinkhole hazard map of the Central Florida region. The developed sinkhole hazard map shows a strong correlation with the reported sinkhole.

As Florida’s population is expanding and greater fluctuations in groundwater levels are being recorded, Central Florida has been experiencing a higher frequency of sinkhole occurrences than ever before. Sinkholes are formed when the soluble limestone bedrock weathers and creates cavities at its interface with the overburden finer-grained soils. The overburden soil then erodes into the limestone fissures, thus weakening the strength and holding capacity of the soil above. This initial stage of a sinkhole is referred to as soil raveling and is the most effective time to perform soil improvement measures, such as grouting, to mitigate further expansion of the subterranean void. Geotechnical engineers and scientists use subsurface exploration techniques such as standard penetration test (SPT) and cone penetrometer test (CPT) to stratify soils and estimate soil properties. These in-field tests can be implemented to detect and evaluate areas of soil raveling which may be a sign of a potential sinkhole. In this study, the authors present the current practice to assess the risk of sinkhole by using SPT and CPT as well as the raveling index (RI). Additionally, a 2D CPT imaging technique is presented to estimate the dimension of raveled soil zone and its engineering applications are discussed.

Sinkholes are a devastating and widespread geo-hazard which poses a significant threat to the environment, infrastructure, and human lives. Many practices involved in the sinkhole assessment are generally of a qualitative nature and largely based on geological characteristics of the karst terrains. This paper aims to present a quantitative analysis of the deformation involving the various behaviors of the geo-materials and interplay of multiple mechanisms involved during the development of sinkholes. It is primarily focused on the influence of rapid and slow drawdown of water scenarios, studied via a coupled hydromechanical model. Rapid drawdown at a higher rate of head drop causes much higher deformation than the slower drawdown which may lead to fast creation of sinkhole. A parametric study of various properties responsible for the sinkhole development is undertaken which involves influence of cohesion, permeability and ground water flow time. The results shows that the higher permeability and higher ground water flow time causes rapid formation of sinkhole. The resistance to the sinkhole formation in the limestone zone is a function of the tensile strength of the rock while the cohesion and friction angle are responsible for the resistance in the clay soil.

Work is underway to develop a 465-acre site to include six large warehouse facilities. The site was an industrial facility in the past, and portions of the site had been used as a disposal area for steel slag and industrial debris. The subsurface conditions include historical fills, buried underground structures, and an unregulated industrial waste landfill in addition to alluvial, glacial, and residual soils. This case study reviews Kleinfelder’s site exploration, geo-hazards encountered onsite, and how the project team addressed these geo-hazards. Kleinfelder’s site exploration program primarily used borings and test pits to evaluate subsurface conditions and supplemented those with selectively located air probes and geophysics to provide a better understanding in certain areas. Hazards considered in the development of the site include karst geology, potentially expansive slag fill, and building over an industrial landfill.

A unique sinkhole limit state risk assessment methodology has been developed that incorporates: (1) an evaluation of primary triggering mechanisms; (2) assessment of key risk factors (past failure history, soil-bedrock type, groundwater flow, and hydrology); (3) an evaluation of human activities (site development, drainage changes, construction activities); and (4) and most importantly, the impacts of extreme weather (precipitation, temperature, flash flooding, erosion). Baseline load and resistance parameters for a given karst area or site are analyzed for normal pre-failure or typical failure limit states. Various load and critical resistance factors are then applied to determine possible failure limit states. A simple graph or map of each critical load or resistance factor with time or location is developed for key parameters such as sinkhole failure history, precipitation, groundwater fluctuations-flow, surface runoff, drainage changes, and any relevant activity by man. The average normal range, upper and lower damage-failure thresholds are identified along with the upper and lower extremes that are associated with major failures and disasters. By overlaying the various load-resistance factors, critical limit states and sinkhole risk are determined for any given area and combinations of loading-resistance conditions. The use of the sinkhole limit state risk assessment methodology is presented for a PA33-Tatamy Road Pennsylvania sinkhole case study.

Interaction of multiple tunnels has become more important in recent years due to an increase in number of tunnels constructed in urban areas. When investigating multi-tunnel interaction problems, previous studies mainly focused on circular tunnels. However, the influence of tunnel shape on crossing-tunnel interaction is still not fully understood. In this study, two sets of three-dimensional centrifuge tests were interpreted to investigate the interactions between perpendicularly crossing tunnels with different shapes of the existing tunnel (circular and horseshoe) in dry sand. To gain further insight into stress transfer in each test, three-dimensional numerical back-analyses were carried out using PLAXIS 3D. Unlike a conventional elastic-perfectly plastic soil model, the advanced hypoplasticity constitutive model with small-strain stiffness was adopted. Results from interaction tests of crossing tunnels are reported and discussed. The influence of tunnel shape on the multi-tunnel interaction is explained.

This paper elaborates on the use of an underground construction technique called concrete arch pre-supporting system (CAPS) in construction of the Tehran subway mass-transit system. CAPS technique is a time and cost effective method consisting of consecutive construction of arch shaped frames throughout the length of underground structures. This method facilitates underground excavation without any surface activity disruption. As part of this research, an underground station in line 3 of Tehran transit system was studied using a numerical technique. A model was developed in the finite element code to represent the pre-supporting structure and final underground structure. Based on the results of the analyses it was concluded by properly modeling CAPS technique in the finite element software, the axial and bending moments developed along final linings of the underground station are significantly lower than forces and bending moments along frame built using conventional cut and cover tunnels. The results of analyses were used to design the final lining of underground station.

The response of existing tunnels to adjacent new tunnelling works is an area of special interest to both civil engineering designers and tunnelling engineers as well as asset owners. Field monitoring is critical as it provides vital data about the response of the existing tunnels that informs future design improvements. This paper focuses on the response of the existing, near century-old Royal Mail Tunnel in the vicinity of bond street London underground station in London, U.K. Cambridge’s ‘Centre for Smart Infrastructure and Construction’ (CSIC) deployed various state-of-the-art instrumentation systems to investigate the behaviour of the existing Royal Mail Tunnel during the construction of a new passenger tunnel as part of London underground bond street upgrade scheme. The instrumentation includes distributed fibre optic strain sensing (DFOS), photogrammetry and strain gauge instrumented tunnel bolts. The monitoring systems combined were able to provide a very good insight into the existing Royal Mail Tunnel behaviour, as the construction of the new tunnel beneath was undertaken.

During the design of a recent transit project, rock anchors were designed to resist high buoyancy forces at multiple underground structures. After considering other options, permanent prestressed double corrosion protected rock anchors were selected. Although such anchors have been used in other infrastructure applications, there are few cases of such anchors for underground structures. To advance the anchor design, the design team reviewed previous precedence at underground and other infrastructure projects, and evaluated the performance of permanent anchors. Identified risks included potential geotechnical failure mechanisms, leaks through the anchored invert slab, corrosion of the tendon and head connection, the inability to access anchor heads after construction, constructability issues and verification of capacity. Mitigation measures included conservative safety factors, groundwater corrosion studies and corrosion protection measures, anchor testing, specialized waterproofing details, and detailed construction sequencing. The findings of the evaluation and the development of the design are presented herein.

An increasing number of soft ground tunnels are built in urban environments where it is crucial that existing infrastructure be protected from potential ground deformations resulting from construction. An important component of protecting this infrastructure is implementing best practices to engage third-party infrastructure owners and develop a ground deformation mitigation plan to ensure risks are fairly allocated among all parties. This approach requires early and close coordination between the project owner and the third parties. During solicitation of a project’s construction contract, coordination should have already occurred and agreements concerning infrastructure protection requirements, included in the bid documents. This allows bidding parties to be aware of the agreed third-party requirements and allows accurate risk and cost assessment. After contract award, monitoring procedures and reporting protocols are important to keep third parties informed. This paper presents the best practices used on the DC Water Clean Rivers Project.

Shield tunneling in complex ground is more difficult than that in homogeneous formation and its construction effectiveness has significant impact on the duration and cost of project. Therefore, a reasonable evaluation of construction effectiveness for shield tunneling is necessary. This paper developed an evaluation model based on fuzzy comprehensive evaluation (FCE) and analytic hierarchy process (AHP). Construction effectiveness was divided into four grades including Extremely Low, Low, High, and Extremely High. Considering eight critical factors, the AHP structure was established hierarchically to determine these factors’ importance weights. Membership functions were derived based on statistical analysis of samples and applied to construct fuzzy decision matrix acquiring the final ranking. A case study was illustrated to demonstrate the feasibility of the proposed model. The model can provide a crucial basis for the analysis on construction difficulty of shield tunneling in complex ground.

This paper introduces a simplified analytical methodology for estimating bending moments and axial loads on buried pipelines due to ground movements caused by tunneling in soft soil. The method combines Winkler models for describing the pipe-soil interaction, with closed-form analytical solutions that use cavity shape-mode parameters for estimating the tunnel-induced free-field ground deformations. Analytical approximations for the vertical and horizontal Winkler spring stiffness coefficients are interpreted from three-dimensional numerical analyses. The proposed methodology is then applied to predict the deformations on an instrumented gas-main in London Clay that was monitored during the construction of tunnels for the Crossrail project at a greenfield site in Hyde Park London. The results show very good agreement between the measured and the predicted strains on the pipe.

Tunnelling under piled structures is becoming more common in urban areas. However, there is limited guidance available for the prediction of settlements and the loss of bearing capacity of existing piles due to tunnel excavation. This paper aims to provide an improved understanding of the response to tunnelling of axially loaded displacement and non-displacement piles. Data are provided from a series of geotechnical centrifuge tests of tunnel excavation beneath single piles in dry silica sand. The tests evaluate induced settlements of the piles at varying levels of initial safety factor (i.e. the ratio between initial bearing capacity and applied load). Furthermore, a previously published analytical approach, based on cavity expansion theory, is used to investigate the variation of the residual safety factor at constant pile load with tunnel volume loss. The outcomes of both centrifuge and analytical investigations illustrate the importance of pile installation method and initial safety factor and improve understanding of tunnel-pile interaction mechanisms.

While the use of building information modeling (BIM) and digital engineering has grown massively in recent years, often being pushed by state initiatives, too frequently it appears to start from the ground up, with the geology and subsurface data being ignored. This paper presents an overview of BIM for geotechnical engineers together with a case study for the silvertown tunnel in London, England, which highlights how the core BIM principles, collaboration, process, Whole Life and 3D Digital Data can be used and applied to geotechnical process, and how incorporating geotechnical data within the wider BIM benefits the collaborating partners.

Geophysical methods and tools are becoming more widely used in the geotechnical and engineering arena. The non-invasive nature and capability to survey significant areas in a rapid and cost-efficient manner typically make them an attractive complementary tool to conventional drilling and invasive investigations. The multi-channel analysis of surface waves (MASW) is one method that has seen growing application in the geotechnical world. We present a case study from an assessment of a historic gold mine site in Colorado. The site was extensively mined in the late 19th and early 20th centuries and left a legacy of collapsed shafts and shallow, typically poorly documented, mine workings. The objective of the survey was to investigate the upper 30 to 50 feet of the subsurface to characterize potential collapsed or backfilled mine workings in advance of the construction of a new mill pond. A total of 40 MASW profiles were collected, along several 1000 foot sections of the targeted mineral veins across the site. While there are numerous surface expressions of old or collapsed shafts across the site, there was limited additional subsurface information to ground truth the geophysics. A significant number of targets in the subsurface were identified in the MASW profiles. A hazards map of the site was produced highlighting potential weak zones or void space in the subsurface for the ensuing earthworks and construction activities.

It’s reported that Ensis directus (a species of Bivalves) achieves exceptionally high penetrating efficiency through periodically expanding/contracting its body during burrowing. This paper provides insights into the cyclic expanding/contracting process in cohesionless granules based on a simplified discrete element method (DEM) framework. In this DEM model, Razor clam is simulated by a circular cavity with a radius changing in a sinusoidal fashion. Different expanding frequencies are considered to study the interaction pattern between the cavity and the surrounding granules. Various stages of expanding process including initial movement, progressive expansion and contraction are captured. A static penetration case is included for comparison of penetration performance. Results positively confirm the contribution of dynamic expansion on the reduction of penetration resistance and energy saving. A critical expanding frequency exists, under which energy saving is optimal. Findings from this study can shed light on the design of smart devices for self-boring or site characterization.

The recently developed instrumented becker penetration test (iBPT) can provide direct measurements of force and acceleration directly behind the driving shoe and at up to four locations along the drill string. This paper describes details of the test system and presents representative results from iBPT soundings performed at a project site where piles, supporting a bridge deck, were installed in relatively clean gravelly soils to a depth of approximately 18 m. The ability of the iBPT system to estimate equivalent SPT N₆₀ values is demonstrated. Dynamic data from individual hammer blows obtained at the tip and along the shaft, as well as fitting of the data with simple spring-dashpot model is presented. Finally, results from static tension load tests showing the measured load distribution along the pile length is presented.

Hydraulic filling dams provides high variability in soil properties. Interpretation of variation of soil profile along a hydraulic fill dam is challenging due to the complexity involved with variability of materials deposited. In this research, an attempt was performed using geostatistical theory to interpret the variation of soil properties by constructing a three-dimensional visualization model for a hydraulic fill dam. Eagle Mountain Lake Dam located in Fort Worth, Texas, constructed using hydraulic filling and wetted and rolled procedure was considered for performing the analysis. Cone penetration tests (CPT) were conducted along the crest and toe of the dam and the results showed that the soil properties change dramatically from one location to another. Data collected was interpolated using ordinary Kriging that is methodology based on Geostatistics. The Earth Volumetric Studio and Mining Visualization System (EVS & MVS) software by C-Tech was used to perform the interpolation. A more reliable soil characterization is developed and a three-dimensional model of soil properties within the dam is presented.

The Norwegian GeoTest Sites infrastructure project, with funding from The Research Council of Norway, is a national research facility for geotechnical research. The infrastructure comprises five test sites in different soils located in Norway and on the Svalbard territory north of Norway. The data collected at these sites will be collated in a web-structured database. The benchmark sites are to be developed as field research laboratories for the testing, calibration and verification of new soil investigation equipment and methods in geotechnical engineering. The research sites cover soft clay, quick clay, silt, medium-dense sand soil conditions and permafrost in Longyearbyen on Svalbard. Earlier Norwegian benchmark sites have been lost due to urbanization and other developments. The new research facility will be operation for at least 10 to 20 years. This paper briefly presents the five test sites, including initial geotechnical characterization data, i.e. in situ and laboratory test results. The soft clay site at Onsøy is of medium sensitivity and has an apparent overconsolidation due to aging. The plasticity of the clay is between 25 and 40% and has similarity to a number of offshore clays. The quick clay site near Trondheim consists of a thick quick clay layer of up to 30 m (remolded strength < 0.5 kPa). The site at Halden consists of intermediate silty materials. The silt is about 10 m thick and normally to slightly overconsolidated. The medium dense sand site near Trondheim in mid-Norway has a 20-m thick homogenous deposit of fine to medium coarse uniform medium dense sand with a predominance of quartz minerals and some plagioclase and micas. The permafrost site near Longyearbyen on Svalbard consists of layered clay, silt and sand with ice lenses, and salt content typical for marine sediments.

The control of induced fracture network generated by hydraulic fracturing treatment plays an important role in predicting the productivity of hydrocarbon resources. In particular, both nature of pressurized injection fluid and in-situ stress condition significantly affect the formation of fracture network. The previous studies have mostly reported qualitative tendency of fracturing mechanism and its manifestation that are partially understood by numerical and experimental results. To better understand the effect of fluid viscosity, a series of experimental tests are systematically performed with cylindrical specimen under axisymmetric condition. The artificially made specimens with cement paste and mortar ensure the homogeneity and isotropy for experimental consistency. Water and oil are served as fracturing fluids at constant pumping rate. The monitoring of stress evolution with increasing pressurization and high-resolution optical endoscopy imaging together allow assessing the morphological characteristics of generated fracture.

Since its inception in the late 1990s, the multichannel analysis of surface waves (MASW) method has become increasingly common for geotechnical site characterization purposes. In most applications, MASW estimates the subsurface stiffness based on analyzing the measured dispersion behavior of Rayleigh waves (i.e., MAS_RW) at a site. The Rayleigh waves are typically generated using vertical impacts on the ground surface, which develop coupled P-SV wave energy. Much research has been devoted to various aspects of MAS_RW, including optimization of survey parameters and the development of robust inversion algorithms. However, little work has been devoted to better understanding the effects of using horizontally-polarized Love waves in MASW investigations (i.e., MAS_LW), despite evidence to support advantages in their use at particular sites. For example, much of the basic information regarding optimal field data acquisition (i.e., source effects, near-field limitations, and receiver spacing) is unavailable or not quantified on the basis of experimental studies that compare MAS_RW and MAS_LW at the same location. This paper presents results from ongoing research that explores the role of source type, source offset, and receiver spacing on MAS_LW data in the field. In this particular study, MASW was used with both Rayleigh and Love waves to characterize conditions at the same site location. Multiple source offsets and receiver spacings were used to generate the dispersion curves and collocation of the arrays and sources allowed comparison between the results from Rayleigh waves and Love waves. There was considerable agreement between the resulting shear wave velocity profiles, though there were some subtle differences in interpretation of the dispersion images and in optimal experimental parameters. This paper summarizes conditions at the site and configuration of the experiments, followed by a discussion of data analysis and interpretation.

The evaluation of subsurface geometry continues to be a major issue for the thousands of bridges across the country with unknown foundations. These bridges pose a threat to the vitality of the nation’s infrastructure, particularly given the difficulties in establishing their vulnerability to scour. In addition, unknown foundations present a major barrier to foundation reuse and rehabilitation. In many cases, geophysical methods can provide a suitable measure of confidence regarding the geometry of these unknown foundations. The multichannel analysis of surface waves (MASW) technique presents a number of potential advantages to evaluate unknown foundation geometry, including increased signal to noise ratio and ability to resolve stiffness inversions. However, very few studies have examined the use of MASW to specifically evaluate unknown bridge foundations. This gap in the literature may be related to concerns regarding vertical and lateral resolution. For example, vertical resolution decreases as the surface waves sample deeper material and the phase velocities are determined by materials over a greater depth range. Additionally, MASW largely averages out lateral variations in stiffness because a layered earth model is used in the data processing. MASW was utilized in this study to determine the two-dimensional (2D) shear wave velocity (V_s) profile over a bridge foundation. The purpose of this testing was to examine the viability of MASW when evaluating unknown bridge foundations, particularly with regards to vertical and lateral resolution. Generally, the results demonstrated that MASW is capable of providing a conservative estimate of depth. MASW proved more capable in accurately assessing the lateral dimension of an embedded foundation, though the results were a function of the survey parameters used during 2D testing.

Seismic traces are obtained during the seismic cone penetration test (SCPTu). These traces are compared to determine the propagation time, which is used to calculate seismic wave velocities. We present a method to quantify the quality of the trace by calculating the signal to noise ratio (SNR). We analyzed a set of 25 SCPTu profiles to investigate how SNR degrades with increased penetration depth. We show that signal-stacking repeated seismic tests can be used to mitigate the loss of signal to noise ratio without a significant penalty to the production rate of the seismic cone penetration test at typical test depths. Our work has implications in the development of best-practice down-hole seismic testing. This may improve the confidence in the reported shear wave velocities and lead to improved shear wave velocity applications.