Geo-Congress 2023: Foundations, Retaining Structures, and Geosynthetics

This paper presents observations and findings gained from a case study which includes the design and construction of around 10,000 CFA piles and drilled shafts for a refinery project in Mexico. A dedicated pile load testing program, i.e., static and dynamic load tests, was developed and executed to check and verify the construction procedure and pile resistance and also for quality control of production piles. This study mainly compares the construction procedures and load-displacement behaviors for the two different types of non-displacement piles. Site-specific correlations between geotechnical parameters such as SPT-N versus CPT-q_c and estimation of fines contents of soils from CPT data are also presented based on results from extensive geotechnical site characterization campaign. The observed production rate of CFA piles was about five times higher than that of drilled shafts. Static pile load test results suggest that the axial compressive pile resistance of CFA piles was approximately 10%–30% larger than that of drilled shafts, while CFA piles showed a slightly lower lateral resistance compared to drilled shafts.

This study focuses on the investigation of adfreeze strength and pullout capacity of helical piles in frozen unsaturated soils. The adfreeze strength plays an important role in capacity of helical piles especially for piles installed in frozen soils, and it depends on hydraulic and thermal conditions, including degree of ice saturation and temperature. An experimental investigation is performed in this study to quantify the impact of initial degree of saturation and changing thermal conditions on the adfreeze strength and pullout capacity. A physical modeling of a single helix pile is conducted in an unsaturated silt layer prepared at four different initial degrees of saturation. The pull-out tests are conducted on modeled piles to measure load-displacement curves at three different temperatures for each degree of saturation. Helical pile capacities are calculated, and adfreeze strengths are predicted from load-displacement curves. The results indicate a significant reduction in adfreeze strength of the pile-soil interface with increasing temperatures and decreasing degrees of saturation.

Caissons are foundation systems of finite width; therefore, consideration of results corresponding to two-dimensional failure wedge (plane strain approach) is not suitable. In the present study, caissons embedded in c-ϕ soil are analyzed using limit equilibrium method considering a three-dimensional failure surface, assumed as oval in the horizontal plane and a logarithmic spiral in the vertical plane. Seismic passive earth pressure coefficient due to cohesion component (K_spc) acting alone is determined corresponding to the critical failure wedge obtained considering resistance due to cohesion (c), surcharge (q), and unit weight components (γ) acting simultaneously. It was observed that magnitude of K_spc increases with increase in seismic acceleration coefficients, which is attributed to larger magnitude of cohesive force due to larger failure wedge acting on the caisson. It was also observed that the increase was much more sensitive to horizontal seismic acceleration coefficient (k_h) compared to the vertical seismic acceleration coefficient (k_v).

An accurate prediction of design capacities of a drilled shaft on weak rock formations is vital for a better design of deep foundations. Irregularities in rock formations due to weathering cause high inconsistency in actual bearing capacities. The assessment of bearing capacity of these rocks typically requires frequent in situ field tests such as drilled shafts load test at smaller intervals (multiple gauges) that are time consuming and expensive. The current design charts that being used in few states such as Texas and Oklahoma do not distinguish between the various types of rock or degradable materials such as intermediate geomaterials (IGM) or shale formations. This study documents several load tests such as Statnamic and bi-directional (O-cell) load cell testing (Osterberg) that were performed across the United States. The principal goal of this research is to improve methods to predict drilled shaft design capacities by accounting for the geologic formations and learning from past projects. This research developed predictive equations to shaft capacities for various rock formations.

Pile foundations may have different types of loads, such as axial, lateral, dynamic loads, and other kinds of loads on them. The present study focuses on the static response of the pile group subjected to axial and lateral loads. Soil, being formed after various natural processes, generally consists of uncertainties in most of its parameters. Uncertainty in geotechnical engineering is mainly attributed to inherent or spatial variability. It is a function of differences in soil properties from location to location, and is focused on here. The angle of internal friction is considered as an uncertain property in the present stochastic study. Uncertainty is incorporated in the form of coefficient of variation. The analysis has been performed using the three-dimensional finite-difference program, i.e., FLAC3D. The prime objective of the present study is to observe the stochastic behaviour of the pile group’s lateral deflection under the combined action of axial and lateral loads. The statistical factors, mean, and variance of the probabilistic density function of the responses are assessed. It has been found that the coefficient of variation in the soil properties significantly affects the deflection magnitudes.

Ground source heat pump (GSHP) technology offers several advantages over conventional space heating and cooling systems. Long-term performance evaluation of GSHP systems is crucial for technical, economic, and environmental sustainability assessment of this technology. Nevertheless, it is often challenging to acquire good quality performance data over a long duration of operation under variable field boundary conditions. This paper correlates, through numerical analysis, thermal performance of a laboratory-scale model pile with that of a prototype pile. Results show that a constant fluid circulation velocity with different diameters of fluid circulation tube produces nearly the same power output per unit length of a geothermal pile. The size of the material domain and the time duration of laboratory thermal performance tests can be decided by carefully selecting the materials with appropriate thermal properties.

Recently derived analytical solutions for soil structure interaction in single energy piles are implemented and extended to investigate load transfer mechanism of energy piles subjected to combined thermo-mechanical loads. To this end, a semi-floating energy pile was subjected to a complete heating-cooling cycle combined with mechanical compressive load, in presence of a head restraint. It was found that the pile shaft and tip are engaged in the transfer of thermo-mechanical load to the soil during heating and a small portion of cooling phase. Nevertheless, once the compressive force at the tip induced by mechanical load is balanced by tensile force at the tip induced by cooling, no further transfer of load at the pile tip is possible with increased cooling. At this stage a semi-floating pile undergoes the transition of the load transfer mechanism from the semi-floating to the fully floating mode whereby the entire thermo-mechanical load is transferred through the pile shaft. Furthermore, the thermo-mechanical load is accommodated by generation of compressive axial stress in the pile during heating. This stress can be significantly larger than the mechanically induced stress. On the contrary during cooling the load is accommodated by generation of tensile stress that can develop within the large portion of the pile.

Selecting the most effective construction method for drilled shafts under the high groundwater table can be a challenging task that requires effective communication between the design and construction teams. Drilled shafts were designed to support a firewall for an electrical substation in central Texas. The subsurface consisted of interlayers of loose sands and soft clays under high groundwater table. The design recommended to install the shafts with temporary casing or slurry displacement due to the anticipated groundwater seepage through granular soils. During the foundation construction, it was very difficult to maintain the stability of the hole and the contractor requested to install the shafts using permanent casings. Therefore, the foundation design was modified to address the construction challenges and ensure that the shafts with permanent casing achieve the required load resistance. Effective and continuous communication among the owner, contractor, and design team during field shaft installation was key to mitigate the unforeseen challenges and successfully complete the project.

This paper describes lateral load tests on single piles, with additional instrumentation to maximize the data measured, along with comparisons between the measurements and predictions and back analysis. An additional lateral displacement measurement by the displacement sensor just above the line of force on the test pile was introduced to obtain the tilt at the pile top level, which is computed based on the difference in the lateral movement over the vertical distance between the displacement sensors. Prediction by numerical modelling, using p-y curve approach, is then compared with the measurements in terms of load-movement response as well as the tilting at pile top for six load tests, and results are presented, demonstrating how it can enhance the soil parameters or models used in the analysis. The numerical analysis also verified that groundwater level has significant influence on the pile response, in the p-y approach especially in sandy soil conditions.

A new project consisting of three basements and 24 floors of luxury residential and commercial complex is developed in the Thu Thiem New Urban, Ho Chi Minh City, Vietnam. It is located next to the bank of the Saigon River which presents adverse geological conditions, including the top 23 m of backfill and very soft clay layers. To optimize the pile design for the project, the Design consultant proposed six piles of various diameters and lengths, including three shaft-grouted and three plain piles, and subjected them to static load tests. The resulting load-settlement curves indicated that the capacities of the shaft-grouted piles were significantly enhanced by this technique. In addition, the readings from strain gauges showed the advantage of shaft-grouted piles in terms of mobilized shaft resistance through different geological strata. As a result, shaft-grouted pile was selected for the final design of piling works to decrease the total pile length, thus reducing construction time, costs, and carbon emissions.

Steel reinforced concrete piles have commonly been adopted as foundations to support container yards in Singapore. However, such a type of foundation causes great difficulties for demolition for future redevelopment. To overcome this problem, a new foundation type has been developed. Non-reinforced rigid inclusion columns together with T-beams are used to support a load transfer platform to provide bearing capacity and reduce settlements for the containers. The arching effect is created in the top sand fill to distribute the loads and control the deformation of the foundation. A conceptual design based on the new approach is proposed. An analytical method is established for the design of the proposed foundation. The key factors controlling the design are discussed. The performance of the proposed foundation is evaluated using 3D finite element analyses.

Jointless bridge designs have become increasingly common over the past several decades, both in the USA and worldwide. The increasing adoption of this alternative is largely due to the poor long-term performance of expansion joints and often prohibitive cost of joint maintenance. While integral bridges typically require flexible foundations to accommodate deck thermal movements, most transportation agencies do not require flexible foundations for semi-integral bridges. This is because, unlike integral bridges, the superstructure of a semi-integral bridge is not directly connected to the abutment and therefore is not expected to experience lateral loading. In this study, 1.5 years of data collected from the drilled shaft foundations of a semi-integral bridge in Texas is presented. This data indicates that semi-integral bridge foundations can also experience significant cyclic lateral loading. In this case, the largest bending moments were observed during the colder months of the year, when the superstructure experiences maximum shrinkage due to temperature decrease.

A better understanding of pile driving resistances and anticipated refusal depth is important to manage installation risks and reduce potential cost. A study to evaluate the performance of steel H-piles driven into thick Wissahickon Schist saprolite layers was conducted for a bridge project in southeastern Pennsylvania. The pile driving resistance is further investigated through a bridge project for these intermediate geomaterials which are completely weathered but retain the fabric and structure of the parent bedrock. All piles in this study were driven to Pennsylvania Department of Transportation (PennDOT) Case 2 Absolute Refusal, defined as 20 blows per inch in soft or decomposed rock, or dense or hard soil strata. Geotechnical resistances from Case Pile Wave Analysis Program (CAPWAP) were compared to evaluate the pile driving refusal criteria. In addition, hammer transferred energy, maximum induced stress as well as pile embedment into saprolite are summarized. The paper presents the results of the pile driving refusal criteria assessment study and provides recommendations to guide both the pile length estimation and geotechnical resistance prediction during the design phase for future projects with similar challenges.

Offshore wind energy can play a significant role in addressing the clean energy policy goals of several countries, where floating offshore wind turbines (FOWT) can be preferred over the conventional fixed bottoms due to the water depth in the envisioned region. Since attractive sites for FOWTs will be located in extensive space in deep water, the potential sites are likely dominated by heterogeneous soils, such as clay to sand. This may require several anchor alternatives depending on soil type, resulting in increased costs and complexities of the single project. Therefore, the deeply embedded ring anchor (DERA) system has developed as a cost-effective solution for mooring FOWTs due to its attractive features: its installability in any soil type, its ability to be deeply embedded, availability to attach to various mooring systems, its multiline potential, and its compact size with high load capacity. In order to investigate the applicability of the DERA to various soil conditions in a specific site, this paper conducts a comparative example study and suggests the optimal design of the DERA in given site conditions. The findings from the study provide a platform to select a mooring system considering geometric constraints and estimate the required physical features of the DERA for achieving the needed load capacity. The results show that the DERA is a feasible and cost-effective alternative for the heterogeneous seabed, shallow water depth, and thin sediment layer due to its attractive features.

Helical piles are composed of steel prismatic shafts and individual or multiple helical plate elements attached to them. These elements are commonly used as foundations in diverse applications such as pipelines, solar renewable energy farms, aquaculture farms, lightweight buildings, pedestrian pathways, among others. Under some of these scenarios, the helical piles are often demanded under vertical loading, for which the strength is usually calculated with bearing capacity equations and then verified with field observations of the required installation torque. Lateral demand provided by wind, earthquake, or inclined loads is also often present in these elements representing the critical design conditions that cannot be as easily verified with close form bearing capacity solutions or field torque measurements. To overcome these design challenges, engineers often rely on more advanced methods such as the p-y method to analyze the response of helical piles shafts under lateral loads. This method has proven to be efficient for pure prismatic elements; thus helical piles are analyzed neglecting any effect from the helical plates. In this paper, a simplified methodology for analyzing helical piles under lateral loading, including the effects of helical plates, is presented considering p-y curves around the shafts in combination with Q-z curves around the plates. The presented methodology is validated with 3D finite element analysis at different cohesive soil conditions and displacement levels.

Construction of buildings, roads, and traffic activities generate ground vibrations that can structurally damage nearby urban infrastructure. The vibrations produced by construction activities can potentially trigger ground deformations in the granular soil conditions and possibly damage the nearby infrastructure. The soil conditions in Florida consist mainly of sandy soil deposits near-surface, and this makes driven piles a commonly used method. In the design of deep foundations, it is important to consider vibrations in the surrounding soils, their effects on nearby soils and structures, and the potential construction issues such as infrastructural and structural damage related to the driving process. This paper presents the state of the practice regarding the effects of pile driving on surrounding soils and structures. A web-based survey was conducted among practitioners in Florida. The perception of several practitioners in the state of Florida about ground deformations and damages to adjacent structures induced by deep foundation installations was investigated. The practitioners who have experienced ground vibrations and deformations were asked to define the susceptible soil conditions and main triggering factors of large ground deformations induced by pile driving. The majority of the respondents found sandy soils with loose to medium relative densities to be the most susceptible soil condition to generate ground deformations, and they observed settlements less than 25 mm up to a distance of 15 m away from the source. Conclusions are drawn regarding the importance of routinely considering ground vibration monitoring during the design phase of deep foundations.

The numerical p-y method is a simplified and practical tool to simulate the nonlinear soil-foundation interaction of a laterally loaded drilled shaft. The cemented soil deposits typically found in Las Vegas Valley, known as caliche, are known for unique material characteristics causing uncertainty in foundation design in the region. As of date, there is no known specific p-y model available to simulate the lateral resistance of caliche material in the numerical programs. In this study, a semi-empirical p-y model specifically developed for caliche material is proposed. Stress-strain relationships from available laboratory tests on caliche were scaled to derive the proposed p-y model. Several lateral load tests conducted in cemented soil conditions in Las Vegas were simulated in the finite-difference program, NVShaft, to assess the applicability of the proposed p-y model. It was then compared to other published models for rock materials. This paper demonstrates the need for site-specific laboratory test data to characterize uncommon geo-materials such as caliche to reduce the uncertainty in the deep foundation design.

The ultimate bearing capacity is one of the main parameters in pile foundation design. Typically, design load calculations can be confirmed by static or dynamic load tests. The static load test is often considered the most reliable method to obtain the ultimate bearing capacity; however, this method is often labor-intensive, time-consuming, and cost-ineffective. Thus, it is of practical interest to predict the ultimate bearing capacity of pile foundations efficiently and accurately in the design phase. This paper presents a machine learning-based framework with integrated physics knowledge for predicting the bearing capacity of pile foundations. A database with 200 static load tests of pile foundations from the literature was used. Several commonly used machine learning (ML) algorithms were trained and tested, including ridge regression, support vector machine, random forest, and gradient boosting machine. As ML models learn functional relationships based on data, trained models with limited data often have unexpected behavior when predicting out-of-domain samples, reducing the reliability of ML models in engineering practice. In this study, prior knowledge in geotechnical field was integrated into these ML models, where shape constraints and additional features were applied to the input space during the model training stage. The results show that the developed ML models have better performance in predicting the bearing capacity than traditional semi-empirical method, and the models integrated with physics knowledge have improved performance.

Surface stress sensitive film (S₃F) sensor uses the 3D deformations of an elastic film to determine the applied normal and shear stresses over the sensor surface. Using such innovative sensors in geotechnical engineering applications promises accurate measurement of the normal and shear stresses. In this study, a method for the normal stress calibration of S₃F sensor was proposed. The effect of the loading area on the normal stress calibration curves was investigated. And the performance of the sensor in measuring the normal stresses in the soil was assessed. The test result revealed that the slope of the normal stress calibration curve has inverse relationship with the diameter of the loading area as long as the loading area is equal or larger than the measurement area. The S₃F sensor also showed its ability to measure the normal stresses within the soil mass with a good agreement with the theoretical stresses.

Karst environments provide unique challenges to both design and construction of any type of infrastructure. Technological advancements in geophysical exploration as well as increased experience in construction in karst areas have allowed for larger and more complex projects in this type of geology. The reason behind this being we are better able to define and map the subsurface on a level unattainable with borings alone, resulting in a higher level of confidence in the stability of the chosen foundation design and in the ability to remediate karst features before they become apparent at the surface. The design and construction of a large multi-story luxury hotel in the karst landscape of Bowling Green, KY, lived up to these challenges. Planned to be built in a development with significant prior sinkhole activity, an aggressive deep foundation system that would resist sinkhole dropouts underneath the building was required. Detailed geophysical and geotechnical studies were performed, and a micropile system with a post tensioned slab on grade design was chosen. Adding to the challenge, the chosen location of the building was over a previously repaired sinkhole. This paper presents the details of the investigation, design, and construction and addresses the challenges and lessons learned throughout the project.

This study proposed a robust two-level Bayesian framework to incorporate the site specific variability for estimating the pile capacity from cone penetration test (CPT) based on LCPC method for LRFD design of pile foundations. The first level of framework considered a prior data for the bias factor and updated it (posterior level 1) using regional test data. In the second level, the posterior of the bias was further updated using the site specific data (posterior level 2). In order to update the Bayesian model in this study, the mean bias (λ) of measured/predicted pile capacities and standard deviation of bias (σ) were obtained from the pile load test database of 33 sites in Louisiana. The Houma Bridges site was selected to implement the site specific variability into LRFD design of piles. The results show that the local values of λ and σ for the Houma Bridge site are (1.09, 0.315). However, the updated λ and σ (posterior level 2) using Bayesian analysis are (1.04, 0.32). The updated posterior parameters for the Houma Bridges site lie between the prior level 2 parameters and the likelihood level 2 parameters, taking into consideration the site specific variability. The posterior of level 2 parameters (λ, σ) can be used to calibrate the resistance factor (ϕ) for LRFD design of piles based on LCPC design method for the specific site.

This paper focused on evaluating the effect of variations in geotechnical properties on the design of deep foundations. The coefficients of variation of undrained shear strength and friction angle (COV_Su, COV_ϕ) and the effect of sampling location on the deep foundation resistance factor were investigated. For the cohesive soil condition, analysis was done in the Red River site in Louisiana, where the weighted average undrained shear strength (S_u) and the COV_Su range from 54.89 kPa to 105.39 kPa, and from 7% to 48%, respectively. For the cohesionless soil condition, analysis was done for the weighted average friction angle (ϕ) of 30°, and for the COV_ϕ range from 0% to 50%. For the mixed soil layers, analysis was performed in Metairie site, where the S_u, ϕ, COV_Su, and COV_ϕ are 23 kPa, 39°, 27%, and 35%, respectively. The results showed that the resistance factor of deep foundation, ϕ_df, decreases with increasing the COV_Su and the COV_ϕ, and with increasing the distance of borehole from the pile foundation. In the site with multiple boreholes, the effect of sampling location on the resistance factor of deep foundations was investigated, and the resistance factor was calculated using the inverse distance weight (IDW) method.

The load response of large-diameter monopiles is highly nonlinear and site-dependent. The design of laterally loaded piles has traditionally relied on the p-y method, which was originally developed for long, slender piles. Direct use of the p-y method for large-diameter monopiles (with small slenderness ratios) may lead to large errors in the estimated lateral pile capacity. Machine learning (ML) methods are superior in solving highly nonlinear problems. In this paper, we developed a hybrid neural network model that predicts the lateral capacity of large-diameter monopiles based on the cone penetration test (CPT) data, pile geometries, and loading conditions. We constructed a hybrid neural network model by combining the convolutional neural network (CNN) and fully connected (FC) deep learning neural network. The model is efficient in training and can generate high-accuracy predictions. A large number of synthesized data obtained based on rigorous finite element modeling were used to train the constructed hybrid neural network model. The developed DL model is able to predict the load-rotation response of monopiles in multi-layered sandy soil. The average relative error in the predicted lateral capacity is 3.1%. A design example is given to demonstrate the performance of the proposed method.

This paper presents the load-mobilization mechanism of single pile (SP) and mono pile-raft foundation (MPRF) embedded in unsaturated sand subjected to hydraulic loading. A finite element-based computer program Plaxis3D was used to develop and discretize the numerical model of soil, SP and MPRF. The solution to the boundary value problem was obtained by implementing a fully coupled flow deformation numerical scheme. The soil was modeled using an elastic perfectly plastic Mohr-Coulomb constitutive model modified by extending Bishop’s effective stress concept. The hysteretic hydro-mechanical properties of sand were incorporated using drying and wetting soil water retention curves (SWRC). The load-settlement (P-δ) response of SP under saturated and unsaturated conditions was validated with 1-g physical model test results available in the literature. The validated numerical model was extended to the case of MPRF. After subjecting foundations to their respective service loads, hydraulic loading in terms of infiltration/evaporation was simulated by applying time-dependent net moisture flux boundary conditions. The obtained results indicated a marked dependency on SWRC and the intensity of hydraulic loading in dictating the settlement and load-bearing responses of SP and MPRF. The hysteretic SWRC influenced the pile-soil relative movement where a higher movement was observed during the infiltration as compared to evaporation, mainly due to the confinement of evaporation within a shallow depth. This phenomenon also affected the mobilization of axial force along the length of SP where higher forces were mobilized up on infiltration (up to 2.7%) compared to evaporation (up to 1.9%). The load shared by the pile component of MPRF increased during evaporation and attained an equalized value, mainly due to the reduction in contact pressure of the raft associated with the reduction in suction stress within the shallow depth. However, a fluctuating load-sharing response for MPRF was observed during infiltration. The outcome of this study provides benchmarking evidence for the mobilization of loads within SP and MPRF considering the coupled mechanical and hydraulic loading.

In this study, structural demands before, during, and after liquefaction-induced lateral spreading were predicted for the deep foundation at an end-bent of a proposed bridge located at the US Highway 76 over Lynches River, Florence/Lee County, South Carolina (SC) site, which is susceptible to strong ground motions and liquefaction. The deterministic method outlined in the South Carolina Department of Transportation (SCDOT) Geotechnical Design Manual (GDM) 2022 and CALTRANS 2017 was used by considering the during- and after-liquefaction scenarios. For numerical study, the finite element software RS2 (v11.0), capable of modeling soil-pile interaction, was used to analyze before-, during-, and after-liquefaction scenarios considering multiple earthquake scenarios. Results show that the structural demands predicted from the numerical method were lower than those obtained from the deterministic method for both during- and after-liquefaction scenarios, except the bending moment induced by the 1994 Northridge and the 1971 San Fernando earthquakes for the during-liquefaction scenario.

The goal of this study is to assess the existing design methods for piles driven in cohesionless soils with an explicit focus on the concept of critical depth. The critical depth is defined as the depth below which the shaft resistance of driven piles does not change; above this depth, the shaft resistance increases with depth reaching to its maximum value at the critical depth. In this study, the critical depth in common design methods for driven piles installed in cohesionless soils is first estimated as a function of the pile width. We then compare the different critical depths from the various design methods to determine the wide variability in such depth among the considered design methods. Thereafter, we assess the validity of the critical depth concept in light of recent arguments that have challenged such a concept. In the end, we present a driven pile design example to compare the ultimate static capacity of the pile estimated using methods that consider the critical depth and those that do not. The significance of the critical depth is then assessed based on the results of this design example.

Many state DOTs have developed or are developing new guidance for driven pile design based on parameters derived from cone penetration test (CPT) site investigations. The response of a driven closed-ended steel pipe pile that was statically load tested for a bridge crossing the Mississippi River at Clearwater, MN, is represented using an elastic continuum solution for axial load versus displacement and axial load transfer. All geoparameters for pile design are supplied by results from seismic piezocone penetration tests (SCPTU) following the procedures outlined in the new 2018 Minnesota DOT (MnDOT) CPT design manual. The pile installation and load test performance were documented as a case study and include load distribution measurements along the length of the pile, allowing separation of side and tip components. The measured and predicted performance agree well, with the latter showing approximate nonlinear behavior using the fundamental G_max profile from the shear wave velocity profile at the site and a simple modulus reduction scheme that tracks with the calculated factored geotechnical resistance from the load testing measurements.

The load-carrying capacity of geotechnical systems (e.g., foundations supporting offshore wind turbines) subjected to static and/or cyclic axial loading could be enhanced using engineered or idealized textured surfaces (or surface elements). The use of surface elements may allow for the development of passive wedges during axial loading, which result in an additional interface resistance to the total load-carrying capacity. To investigate the effects of surface pattern and asperity height on the static and post-cyclic interface shear response, the cyclic interface shear test (CIST) device, which was developed by the research team, was used. To achieve this, a smooth plate representing the surface condition of commonly used steel piles and four engineered textured plates (i.e., rough plates) of different level of roughness (i.e., asperity height of 0.35, 0.65, 1.25, and 1.75 mm) were 3D printed, and then the soil-plate interface was subjected to monotonic and cyclic axial loading. The interface shear tests were performed in a normally consolidated sand-kaolinite mixture. In this paper, the experimental setup (i.e., CIST), sample preparation, and results of a series of static and displacement-controlled cyclic interface shear tests on smooth and textured (rough) plates are summarized and compared to the static and post-cyclic soil-smooth shear strength (no surface elements). For static tests, the interface shear strength increased with asperity height, and this increase ranged from ~55% to 105% of the soil-smooth interface shear strength. Similarly, the post-cyclic interface shear strength increased with asperity height, and this increase ranged from ~167% to 266% of the soil-smooth interface shear strength. The preliminary test results included in this paper also show that the interface shear resistance of surfaces with structured elements is controlled by asperity height (h) and asperity spacing to height ratio (Sc/h ratio).

A PDEA, Duckbill model 88 II (DB-88 II), was selected and tested in a laboratory pull-out test in a silty lean clay conducted in a soil box measuring 1 m in length, 1 m in height, and 0.6 m in width. The sampled soil was compacted in a soil box at 95% compaction and 10.5% water content based on the standard compaction test results. The PDEA was installed by driving the installation rod with a hammer nearly the bottom of the box at 0.9 m. The PDEA was pulled upward using a hydraulic jack to measure the pull-out resistance of the anchor. The pull-out load, displacement, and soil surface movement were recorded with a load cell and LVDTs. A pull-out load-displacement curve was obtained and analyzed to determine the ultimate pull-out load from the test. A prediction equation by DAS 1980 was also used to estimate the pull-out capacity of the anchor embedded in the box. The comparison between the measured ultimate pull-out load and the estimated values from the equation indicated that there is a considerable discrepancy between the value estimated from the equation and that from the actual controlled pull-out test.

Cantilever sheet pile walls are generally used to retain the moderate height of excavation in both cohesive as well as cohesionless soil as a temporary or permanent structure. These structures are highly vulnerable to seismic conditions due to the non-availability of suitable anchors or mass to strengthen them. In practice, a surcharge in the form of a strip load of finite width is generally present on the backfill. Therefore, in the present study, cantilever sheet pile walls having strip load on the backfill are analyzed using an explicit finite difference-based computer program FLAC2D. A parametric study is done by varying the seismic acceleration coefficients, excavation height, width, and distance of the strip load from the cantilever sheet pile wall. The results show that a strip load of width 2–3 m (among chosen widths) placed on the backfill gives the maximum bending moment in the cantilever sheet pile wall.

In retaining wall design, the Coulomb and Rankine active earth pressure theories is commonly used. However, because the above theories include various assumptions, determining the accurate earth pressure distribution acting on the retaining wall is limited. When estimating the earth pressure of a retaining wall, it is commonly assumed that the backfill material is cohesionless; nevertheless, the cohesion force occurs in the direction of resisting sliding, and the active earth pressure decreases. Many research studies have recently been performed to reduce the earth pressure acting on the retaining wall through various materials and the active earth pressure taking cohesion materials into account. In this study, a soil tank apparatus which has a rotatable wall on the side is used to assess the lateral earth pressure of different backfill conditions with wall rotation. The lateral earth pressure according to the rotation of the wall was measured, and the earth pressure reduction effect was verified by forming BPST (biopolymer-based soil treatment) layers that can vary the shear strength parameter in the sandy soil. The lateral earth pressure rapidly decreased as the wall started to rotate. The improvement effect of the shear strength parameter was negligible in the wet (initial) condition of the BPST, and hence had little effect on the lateral earth pressure behavior. However, the lateral earth pressure reduction effect occurred in the BPST dehydrated (dried) condition by restricting the lateral movement of soil particles by improving cohesion and working similarly to the relief shelf of the retaining wall.

The usage of reinforced retaining walls is developing all around the world. Additionally, the variety of reinforced walls would increase by improving polymer science and introducing new reinforcement types. This paper studied the seismic behavior of geocell-reinforced retaining walls using shake table tests. Four models were subjected to variable–amplitude harmonic excitations in two main stages. The primary variable includes the effect of geocell facing configuration on the walls’ seismic response as the main component of retaining structure. Results showed two primary failure mechanisms, overturning and bulging. Also, lateral displacements and settlements would decrease by changing the configuration and using more geocells in the wall’s top layers.

This paper outlines a detailed multi-year investigation of the reduction in tensile strength for one particular coated polyester (PET) geogrid exposed to pH values ranging between 10 and 11.4. Arrhenius modeling was used to extrapolate the degradation rate of the geogrid tensile strength to 20°C over a 75–100-year design life and determine appropriate durability reduction factors for a pH range of 10–11.4. This durability reduction factor in elevated pH environments will allow for the calculation of long-term design strength (LTDS) for the geogrid reinforcement tested to be used in a greater range of pH environments, often encountered in the mechanically stabilized earth (MSE) industry.

Mechanically stabilized earth (MSE) walls have been used extensively in transportation systems that are designed for a service life of several decades. MSE walls often include steel strips’ reinforcement (typically galvanized steel strips) within granular backfill to stabilize the backfill through anchorage. In MSE walls, the reinforcement may rupture or be pulled out from granular backfill. In the current MSE wall design method, the strength and pullout resistance of reinforcements are evaluated to ensure the stability of the walls. The pullout resistance represents the reinforcement-backfill interaction. Due to environmental effects, some reinforcements deteriorate by corrosion and lose their structural capacities. Moreover, water cycles from precipitation promote migration of fines through the granular backfill. Migrating fines may accumulate in the granular backfill, clog drainage, and retain water—which in turn accelerates the corrosion process—and affect the reinforcement-backfill interaction. Therefore, corrosion and migration of fines could affect the strength and the mobilization of tension in the reinforcement. So far, limited studies have been carried out to investigate the performance and behaviors of the MSE walls when they are subjected to both corrosion and migration of fines. The focus of this parametric study is to investigate the combined effects of corrosion and migration of fines on the global stability of MSE walls. The limit equilibrium (i.e., the Bishop simplified method) in ReSSA Version 3.0 program was used to determine the potential failure surfaces in the walls and calculate their corresponding factors of safety. The combined effects were simulated by varying the properties of steel strips and reinforced fill. The results indicated that when corrosion (with a degree of 50%) was simulated, the factor of safety marginally decreased by approximately 9.5%. However, when both corrosion (with a degree of 50%) and migration of fines (with fines content of 15%) were simulated, the factor of safety decreased by approximately 13.5%.

The main objective of the study is to demonstrate the use of mixed recycled aggregate (MRA) as a sustainable replacement for locally available Yamuna Sand (YS) in the design of mechanically stabilized earth (MSE) walls. The physical properties like gradation, compaction, and shear strength of MRA and YS were evaluated and compared with the Indian codal provisions. The test results showed that the gradation and compaction of MRA and YS were similar. However, the shear strength of MRA (44°–45°) was better than YS (38°–39°). The pullout testing on MRA and YS was carried out, and the results were used to design a single-tier MSE wall of heights 3, 4, 6, 8, 10, 12, and 14 m with these materials as structural backfill. The economics of using these fill materials with the cost of transporting them to 50 km has also been worked out. The pullout results showed that the interface friction (µ_S/GSY) of MRA was higher than YS. The economic analysis showed that using MRA was beneficial for wall heights above 8 m and can be economically transported to 50 km compared to YS.

Geosynthetic-reinforced soil (GRS) walls have been recently used as bridge abutments to directly support spread footings on the reinforced soil mass. This application reduces the requirement for using traditional deep foundations, such as piles or drilled shafts, to support bridge beams. GRS abutment walls are generally subjected to high footing loads that are close to the wall facing. Although GRS abutment walls with modular block facing have been the subject of a number of studies, there are limited methods to predict the profile of the lateral facing deflections along the height of the GRS abutment walls. Lateral deflections along the facing of GRS walls are of significant importance and are difficult to predict. In practice, design engineers need numerical modeling or software to predict the deflection profile. The objectives of this study were to develop an analytical approach to estimate lateral deflections of the wall facing along the height of the GRS abutment walls. Two sets of equations were developed, and experimental test results were used for verification of the proposed analytical approach. There is agreement between the results from proposed approach and the measured data. The maximum lateral deflections predicted from the proposed equations are almost identical to the measured data. The facing lateral deflection profiles with depth are within close range of measured data. The proposed analytical equations for determining lateral deflections provide an effective and simple tool in design of the GRS abutment walls.

Back-to-back mechanically stabilized earth walls (BBMSEWs) have been increasingly used in the world, mostly for bridge abutments, highway and railway embankments, and coastal levees. The Federal Highway Administration (FHWA) provides guidelines for the design of BBMSEWs reinforced with steel reinforcements or geosynthetics under self-weight or vertical loads, which depend on gap or overlap distances between two-side reinforcements and wall height. However, BBMSEWs have also been used to support lateral loads or been subjected to seismic loading. Researchers have conducted numerical studies and centrifuge/shaking table tests to examine the behavior of BBMSEWs and compare some of the results with the FHWA design guidelines. This paper provides a technical review of recent studies on BBMSEWs and summarizes key findings from several important studies. The technical review is focused on the behavior of BBMSEWs, including critical slip surfaces, lateral earth pressures, tension in reinforcement, deformations of wall facing, and stability, and evaluates the effects of wall width to height ratio and reinforcement gap or overlap distance on the performance of BBMSEWs under static and dynamic loads, including seismic loading. The reduction of the back-to-back wall width reduces the lateral earth pressure behind the reinforced zone, the wall lateral deformation under self-weight, the maximum tensile force in reinforcement, and lateral resistance under lateral loading, but increases the factor of safety and the wall lateral deformation under seismic loading.

Full-scale tests on instrumented geosynthetic reinforced soil (GRS) piers were performed to investigate geosynthetic stiffness and strength influence on axial load-deformation performance. Each pier was constructed with poorly graded Florida limestone aggregate, segmental facing blocks, and biaxial woven polypropylene geotextile. The vertical displacement of the top of the pier, the deflected shape, and tensile strains in the reinforcement were monitored during the test. Results indicate the position of maximum lateral displacement shifts from the top to two-thirds of the wall height as the load increases. Measured reinforcement strains are greatest in the middle layers of the pier. At the upper layer, the reinforcement strains are greater close to the edge of the blocks, while at the middle layers they are greater at the center of the geotextile. Stress-strain curves developed from the measurements show ultimate bearing capacities are 17%–36% greater than the predictions using the FHWA recommended equation.

Mechanically stabilized earth (MSE) walls underlain by weak soil are prone to base sliding failure which causes the structure to fail in the long run. Recycled plastic pins (RPP) can be a viable and sustainable solution for increasing the base resistance of MSE wall. The objective of the present study is to evaluate the long-term performance of MSE walls reinforced with RPPs at the base. A field-scale study was conducted by constructing four identical MSE walls in Irving, Texas—three of the sections were reinforced with 3.05 m long RPPs having different combinations of cross-sections and spacings, whereas the other section was left unreinforced. All the sections were identically backfilled with a soil height of 1.5 m initially. The sections were instrumented with vertical inclinometer casings along with pressure plates to monitor the displacement and pressure variance at the wall base, respectively. After more than three years of monitoring, the field data indicated that the unreinforced section failed after only six weeks from construction while the reinforced sections are still in a stable condition with minimal displacement. In addition, 66%–76% reduction of lateral earth pressure was observed against the face of the wall in the reinforced sections in comparison with the unreinforced section. The RPPs acted as a shear key to restrain the base sliding of the wall. Based on the study it can be summarized that RPPs can be used as a long-term solution for increasing the base resistance of MSE wall.

Ultra-lightweight foamed glass aggregate (UL-FGA) is a sustainable choice lightweight fill and is manufactured across the United States. The manufacturing process uses curbside-collected (post-consumer) recycled glass as feedstock. The low density and high permeability of UL-FGA may be especially beneficial when used as retaining wall or mechanically stabilized earth (MSE) retaining wall backfill if there are soft soils, sensitive structures, or utilities present in the subsurface. Additionally, the use of UL-FGA as a lightweight backfill allows for the structural optimization of the wall itself including seismic loads. Details and considerations for using UL-FGA in traditional and MSE wall design are presented in this paper. Additionally, the implication of using a low density and highly frictional retaining wall backfill on lateral pressures is quantified for static and seismic conditions.

Below I-75 in Detroit, Michigan, the advancing of a tunnel boring machine (TBM) for the construction of a 16-ft (4.9 m) diameter storage and drainage tunnel experienced sudden subsidence. The TBM was damaged to the extent that its shield, cutting head, and extensive interior components needed to be extracted and replaced along with several completed tunnel segments. Subsequently, the tunneling contractor engaged their designers and specialty subcontractors to develop a resolution to ingress the TBM to repair the tunnel liner and critical components on the TBM. The tunneling contractor needed the repair shaft to have a depth of 99 ft (30.2 m), with an unobstructed plan dimension of 50 ft (15.2 m) to accommodate the large components that needed to be removed and replaced, effectively eliminating the use of an internally braced excavation solutions. A unique compression ring was analyzed, although, with the existing tunnel liner obstructing the closure of the compression ring at depth, an innovative solution using a “horseshoe” compression shoring system was developed/analyzed below the tunnel’s crown. Utilizing PLAXIS and SAP2000 models, the 3D soil-structure interaction around the “horseshoe” was used to determine the concentrated stress and deformations generated having an opening in the compression ring. Through very tight installation tolerances, this paper will present the site conditions, innovation geo-structure design, 3D FEM analysis, construction, and challenges associated with this repair shaft.

Many integral abutment bridges (IABs) have been constructed due to their economic advantages as they lead to lower construction, maintenance, and repair costs during the bridge life cycle. However, the seasonal temperature-driven lateral movements may cause a complex behavior between the bridge structure and the soils behind and under the abutment, which could lead to undesirable results such as soil densification, void formation, and approach slab settlement. The response of the IAB to those movements is highly dependent on the overall structure, geometry, and location of the bridge. Furthermore, if an IAB is curved, it adds more complexity to its behavior. In this study, we attempt to investigate the behavior of a curved IAB via field monitoring continued through one seasonal cycle. It is observed that both abutments rotate and translate toward the backfill soil in summer because of the thermal expansion of the superstructure. This thermally induced movement increased the lateral pressure up to 75 kPa. The lateral soil pressure begins to drop as the temperature falls, but it does not return to its initial value while the abutments contract. It implies that irreversible deformation may occur during seasonal temperature changes. The obtained results also suggest that the foundation soil, the geometry, and curvature of the IAB, and the skew angle in the abutment could greatly influence the bridge’s behavior during seasonal temperature changes.

Recent laboratory investigations indicate that low-to-medium plasticity subgrade is vulnerable to subgrade fluidisation due to excessive local hydraulic gradients that develop under cyclic loading. This study primarily investigates the role of geosynthetics to dissipate accumulated excess pore water pressure (EPWP), and minimise particle migration and subgrade fluidisation in typical railway track environments using the dynamic filtration apparatus (DFA). The experiments indicate there is an upward migration of moisture and fine particles towards the ballast-subgrade interface which cause the soil specimen to soften (slurry) under undrained cyclic tests. The combined prefabricated vertical drains (PVDs) and geocomposite system can dissipate the rapid accumulation of EPWPs due to the reduction in drainage path lengths and additional confinement at the ballast and subgrade interface. The excess pore pressure gradients (EPPG) that developed at different depths of the soil specimens were measured to assess the potential for the upward migration of fine particles.

The geosynthetic reinforced soil-integrated bridge system (GRS-IBS) is becoming widely used for transportation infrastructure. Most of the reported GRS-IBS case histories were constructed on relatively stiff foundation soil layer, and all showed good service performance. This paper presents a numerical study of the deformation behavior of GRS-IBS under service load conditions, with the objective of evaluating the influence of foundation soil conditions. Numerical simulations were conducted using the finite difference program FLAC for GRS-IBS constructed on granular foundation soils with different densities. The granular foundation soil and backfill soil were characterized using a nonlinear elasto-plastic model that incorporates the Duncan-Chang hyperbolic relationship and the Mohr-Coulomb failure criterion. Foundation soil parameters were selected according to data reported in the literature, and the soil stiffness and strength increase with increasing density. Geogrid reinforcements were characterized using linearly elastic-plastic cable elements. Various interfaces were included to simulate the interaction between different components. Simulation results indicate that increasing the foundation soil stiffness and strength effectively reduce facing displacements, bridge seat settlements, and foundation soil settlements, but also produce larger vertical compressions of the GRS abutment. Results provide insights for the application of GRS-IBS for different granular foundation soil conditions.

Stone columns (SC) are widely used for ground improvement of soft clay. Geosynthetic can be used as encasement for conventional stone column, which forms geosynthetic encased stone column (GESC). This technology can reduce the lateral displacements of stone column and improve the bearing capacity in soft clay through the restraint of geosynthetic encasement. This paper presents a numerical study to investigate the dynamic response of SC and GESC, with the goal of evaluating the effect of geosynthetic encasement. Simulations were conducted using the finite difference program FLAC3D to investigate the response of SC and GESC in soft clay ground under dynamic loading. Both the stone column and the soft clay were characterized using nonlinear elasto-plastic models that consider the hysteretic behavior. Geosynthetic encasement was characterized using linearly elastic geogrid elements. The dynamic response of SC and GESC for a sinusoidal motion was investigated and compared. Simulation results indicated that the geosynthetic encasement can effectively reduce the settlements of stone column and soft clay under dynamic loading.

Good roadway engineering and construction practices typically require embankment soils and granular fills to be compacted at optimum water content. This approach provides the best performance for the roadway structure. However, the water content in these materials tends to increase post-construction due to factors like precipitation infiltration and capillary action. Slight increases in moisture to these materials can negatively impact the life expectancy, behavior, and maintenance costs of our transportation network. When an enhanced moisture management geosynthetic first appeared in the early 2010s, the only thing that was truly understood about it was that it moves water out of civil structures. Since that time, more than two dozen research projects have quantified the mechanical and hydraulic benefits provided by the geosynthetic. This paper will provide several research updates on these benefits in various climates, soil conditions, and applications. These applications include frost heave mitigation, reduction of damage from expansive clays, decreasing the moisture contents in granular bases as well as subgrades, all in saturated and unsaturated subgrade conditions.

Narrow back-to-back geosynthetic reinforced soil (BBGRS) walls with aspect ratios of 0.5–1 are commonly used for roadway and railway bridge embankments having limited width. Although narrow BBGRS walls are widely used, only a few numerical and physical modeling studies have reported their seismic response. Hence, this study performs a numerical study to understand the seismic behavior and observe factors affecting the seismic response of narrow BBGRS walls. The result of this study identifies the value of critical acceleration for narrow BBGRS walls. This study highlights the importance of considering the velocities of earthquake motions while estimating the response of narrow BBGRS walls. These results aid the designer in developing a design methodology for accurate response prediction for BBGRS walls.

The presence of a filter media impedes water flow in terms of generating excess pore pressure and decreasing the flow rate of the soil-filter system compared to the flow rate in soil. Therefore, the hydraulic conductivity requirement includes excess pore pressure and flow rate requirements. Different criteria for granular and geotextile filters are currently developed empirically based on experimental investigations. This paper proposes an analytically derived design criterion for the hydraulic conductivity requirements for granular and geotextile filters. The derivation has shown that the hydraulic conductivity requirements of pressure head and flow rate are satisfied with a sole condition of hydraulic conductivity of filter greater than or equal to the hydraulic conductivity of soil times the hydraulic gradient in soil. The coefficient of variation of saturated hydraulic conductivity is often greater than 50%, reflecting a need to quantify the uncertainty in the design criterion. Therefore, partial safety factors are developed for the proposed criterion to quantify the variabilities of hydraulic conductivities of soil and filter such that the requirement is satisfied at targeted reliability.

Current geotextile filter design methodologies rely on geotextile apparent opening size (AOS) measurements obtained from ASTM D 4751. Even though a typical geotextile sample has a range of opening sizes, the current standard of practice is to use ASTM D4751 to obtain a single AOS value that is used for filter design of soils with a wide range of particle sizes. The AOS is a property of the geotextile that indicates the approximate largest particle that would effectively pass through the geotextile. It is also commonly referred to as the O₉₅ of the geotextile. In recent years, geotextile pore size distribution (PSD) is being obtained in accordance with ASTM D6767. PSD results yield a spectrum of opening sizes that represent a geotextile’s ability to retain soil particles, as opposed to a single “largest opening size” value that is obtained from AOS testing per ASTM D4751. A new geotextile filter design method using multiple retention criteria has been created through a synthesis of the existing body of knowledge combined with laboratory testing to validate the new design methodology.

This paper summarizes the results of an experimental program that investigates the effect of the hardness and printer-induced roughness while using 3D printed prototypes to study the shear behavior of soil-continuum interfaces. Using PLA polymer, different planar continuum material prototypes were fabricated with a fused filament fabrication (FFF) 3D printer. Two different soils, namely sand and clay, were taken, and their interface shear behavior with the 3D printed surfaces was investigated. The interface shear responses of the 3D printed prototypes are compared with those of factory-made commercial smooth HDPE geomembranes to understand the effect of hardness alone. The results show that the secondary roughness and the hardness of the 3D printed continuum materials influenced both clay and sand interfaces, with clay and sand showing an increase in the peak interface friction angles of almost 84% and 22%, respectively, in the 3D printed prototypes when compared to a factory-made geomembrane.

The study investigates the effect of particle shape, hardness of continuum material, and normal load on the shear response of non-dilative geomaterial contacts using custom-built micromechanical shear testing apparatus. For this study, two different types of particulate materials (sub-angular sand and rounded glass beads) and continuum materials (smooth geomembrane and steel) are selected to test four different types of interface contacts. The results reveal that the friction coefficient and mechanism are dependent on the particle shape, continuum material hardness, and normal load. The friction coefficient increases with an increase in the angularity of the particle and decreases with an increase in the hardness of the continuum material. The friction coefficient initially decreases and then increases with an increase in normal load due to change in frictional mechanism from sliding to plowing at the critical normal load. The critical normal load decreases with an increase in angularity and increases with increase in hardness. Further, the mechanism change is corroborated with the shear-induced surface changes measured using a stylus profilometer.

Geocell, a three-dimensional geosynthetic product made of high-density polyethylene (HDPE), can provide additional confinement for the base aggregate material. The base layer of a flexible pavement plays a key role by distributing the traffic load from the surface layer to the underneath weaker subgrade layer. This study aims to evaluate the performance of geocell-reinforced flexible pavement sections based on an automated plate load test (APLT). Three geocell-reinforced pavement sections were constructed on a farm to market road near Dallas-Fort Worth metroplex, Texas, by replacing the existing crushed stone base layer with geocell-reinforced, recycled asphalt pavement base layer of 150 mm, 200 mm, and 300 mm thickness. APLT tests were conducted on the newly constructed reinforced sections and the existing roadway sections. Each APLT test had 504 cycles with three different magnitudes: 344.7, 689.5, and 1034.2 MPa, and three different frequencies: 0.1, 1.0, and 2.0 Hz. The results obtained from APLT showed that the permanent deformation of the base layer decreased with an increase in the geocell layer thickness. An increase in frequency from 0.1 Hz to 2.0 Hz decreased the resilient deformation by 23.8%, 25.8%, and 27.8% for 150 mm, 200 mm, and 300 mm geocell-reinforced sections, respectively. Furthermore, the surface modulus of the reinforced section increased significantly with the increase in frequency and the thickness of the geocell-reinforced sections.

Woven geotextiles have been commonly used to reinforce or stabilize slopes, walls, and roads. Soil-geotextile interface shear strength is an important design parameter for these applications. Under different geometrical and/or loading conditions, the geotextile may be sheared in different directions. Therefore, it is important to understand how interface shear strengths change with shearing directions. This study aimed to investigate and compare the interface strengths between sand and woven geotextile by large interface shear tests performed in three shearing directions: (1) 0° (machine), (2) 45° (diagonal), and (3) 90° (cross-machine) under three normal stresses of 12.5, 25, and 50 kPa. The large interface shear test device consisted of an upper shear box and a lower shear box in similar dimensions of 100 mm high, 300 mm wide, and 300 mm long. One type of woven geotextile consisting of polypropylene fibers was investigated. A river sand at a dry condition was used and compacted to a relative density of 75%. The interaction coefficient between the sand and the geotextile was calculated for each test. The test results show that the shearing direction had obvious effects on the peak interface shear strength and the volumetric change during shearing. The interface shear strength and the volumetric change at the 45° shearing direction had a combined effect from those in the machine and cross-machine directions.

One of the crucial aspects in design of a landfill capping is the interface behavior between the different layers of the cover system, from the leveling layer above wastes up to the topsoil. Design guidelines and international codes require a geotechnical stability analysis to be performed along every interface. The critical interface is the one which gives the minimum shear resistance, in terms of friction angle and adhesion. Evaluation of the correct values to be used is then essential. Shear resistance at the interface between different geosynthetics or between a geosynthetic and a soil can be measured through laboratory tests. Testing methods are EN ISO 12957-1 and ASTM D5321 (both for direct shear test) and EN ISO 12957-2 (for inclined plane). The paper briefly describes direct shear and inclined plane testing methods and enhances pros and cons. In fact, in the last 25 years the authors have coordinated a great number of the above tests with different types of geosynthetics and soils. The main results of these tests are reported in the paper. The purpose of this work is to validate and increase the already big database of interface strength measured with direct shear tests and to evaluate the differences with the results obtained for the different types of tests. This can give to designers the chance to have a critical approach toward the most suitable testing method to be used according to the specific needs of a project.

The thermo-hydro-mechanical (THM) shear behavior of the interface between a textured geomembrane (GMX) and a geosynthetic clay liner (GCL) was investigated using large-scale direct shear tests. The GCL was comprised of granular bentonite sandwiched between two non-woven geotextiles bonded by needlepunching. The geomembrane was textured high density polyethylene. Influence of normal stress, hydration condition, and temperature on interface shear behavior was evaluated, and changes in the surface characteristics of the interface were documented photographically. The peak shear strength of the GMX/GCL interface was higher under dry conditions than when hydrated. In some cases, two peak strengths were observed in the hydrated condition, whereas shearing under dry conditions consistently yielded only one peak strength. The peak shear strength and large-displacement shear strength of the GMX/GCL interface were highest at room temperature. Increasing the temperature resulted in a reduction in shear strength and less post-peak strength loss. Three failure modes were observed: GMX/GCL interfacial failure, partial interface/internal GCL failure, and internal GCL failure. Increasing normal stress and temperature caused a transition in the failure mode between interfacial failure and internal GCL failure. Extrusion of bentonite into the interface under hydrated conditions also influenced the interface strength and the failure mode.

Finite element limit analysis was used to investigate the performance of an axially loaded strip footing with structural skirts resting on sandy soils in this work. Three separate cases were investigated to determine the influence of skirts on the performance of skirted footing: (1) effect of skirt length and angle of internal friction, (2) effect of vertical load on lateral capacity, and (3) effect of skirts on footing settlement. The bearing capacity ratio was used to show how skirt addition improved the bearing capacity of surface foundations. Analysis of the numerical and experimental study results revealed that the inclusion of skirts improves the bearing capacity and settlement behaviour of surface foundations on sand. The improvement in magnitude increases with increasing skirt depth. Laboratory studies on small-scale foundation models were also conducted to investigate the behaviour of skirted foundations subjected to vertical loads.

Shallow foundation on cohesionless soils is one of the most economic and technically simple alternatives for bridge foundations. Typically, deep foundations (e.g., piles, drilled caissons) are explored only if shallow foundations are not technically viable, which in most cases depend on foundation settlement. Geotechnical design standards often limit the magnitude of allowable settlement for shallow foundations (such as 25 mm). However, estimation of foundation settlement on cohesionless soils depends not only on soil and foundation properties but also on the empirical/semi-empirical or numerical methods used for settlement computation. This paper compares shallow foundation settlement using four empirical/semi-empirical methods: elastic half-space method, Hough method, Schmertmann method, and Christian and Carrier method. Computed settlements are compared with settlement monitoring data collected for two ramp bridges over Interstate 80 in Monroe County, Pennsylvania. It was observed that modulus of elasticity and influence depths are not the same for all these methods which affected computed settlements. A comparison of the measured and computed settlement was also performed using the same influence depth and the same modulus of elasticity in all of the four empirical/semi-empirical methods.

The anchor foundation system has been used successfully to support transmission lines and onshore wind turbines due to its inherent resistance to overturning moments, which will result in a large rotational stiffness. In this paper, the complex load transfer mechanism of the anchor foundation system is investigated in detail, and its performance is evaluated to demonstrate the effect of pre-stressing of the ground anchors. Three-dimensional numerical simulations were conducted to investigate the soil-structure interaction of the anchors and of the concrete cap in detail. The soil constitutive model used in this study is the well-established and documented hardening soil model, which was calibrated with laboratory tests. The selected soil model can capture the effective confining stress-stiffness dependency and the expansion of the yield surface, which is necessary to capture the ground improvement achieved by prestressing of the anchors. The numerical models demonstrated that the ground anchors’ prestress magnitude has significant effect on the foundation response through two mechanisms: the ground improvement and additional resistance to uplift forces. The results demonstrated that the anchor foundation system is an efficient and cost-effective solution for structures under large overturning moments, with superior performance in maintaining the serviceability requirements under large load demands.

The existence of a metastable skeletal structure in natural deposits of structured clays influences soil to behave in a significantly different manner than that expected from a reconstituted specimen prepared in the laboratory. Degradation of soil structure with continuous plastic deformation is identified as the key reason behind such behavioural disparity. This research emphasizes the need to consider in situ soil structure, its degradation under loading, and the consequent evolution of stress-induced anisotropy in bearing capacity analysis of square footings in structured clay. The bearing capacity factor for a square footing in structured clays demonstrates a substantial decrease due to the soil destructuration process. The effect of the footing-soil interface condition on footing bearing capacity is also studied. Moreover, results from a field load test conducted on a square footing in structured clay in Brazil are predicted through finite element analyses. Numerical prediction is in very good agreement with reported field data.

Tire-derived aggregate (TDA) has been adopted in multiple civil engineering applications as a lightweight fill that has the additional benefit of being a recycled material. While the compression response of TDA with small particle sizes has been studied in the literature, there is a lack of data on the response of Type B TDA with larger particles having a maximum dimension of 300 mm. This study focused on assessing the one-dimensional compression response of an 810 mm-thick layer of Type B TDA under quasi-static uniaxial compressive stresses in a large-scale rigid container having a length of 5.029 m and a width of 2.184 m. First, this paper presents the results of one-dimensional compression response of Type B TDA under a constant rate of strain test up to a vertical effective stress of 20.4 kPa, which was then maintained for 1 h to evaluate the creep response. A bi-log-linear compression curve fitted to the nonlinear compression curve for Type B TDA had compression and recompression indices of 0.32 and 0.04, respectively, that are greater than those of most soils. A hyperbolic model was also found to provide a good fit to the data. A secondary compression index of 0.0029 was observed during creep testing, within the range of values obtained from studies on TDA with smaller particle sizes.

The objective of this study is to develop data-driven predictive models for permanent settlement of rocking shallow foundations during seismic loading using multiple machine learning algorithms and supervised learning technique. Data from a rocking foundation database consisting of dynamic base shaking experiments conducted on centrifuges and shaking tables have been used for the development of k-nearest neighbors regression, support vector regression, and random forest regression models. Based on repeated k-fold cross validation tests of models and mean absolute percentage errors in their predictions, it is found that all three models perform better than a baseline multivariate linear regression model in terms of accuracy and variance in predictions. The average mean absolute errors in predictions of all three models are around 0.005 to 0.006, indicating that the rocking induced permanent settlement can be predicted within an average error limit of 0.5% to 0.6% of the width of the footing.

By combining the modified pseudo-dynamic method with the lower bound finite element limit analysis technique, the bearing capacity of an embedded strip footing placed on a soil slope and under seismic loading is estimated. A series of parametric studies by varying coefficients of seismic acceleration, friction angle of soil, inclination of the slope, embedded depth of footing, and soil damping ratio is carried out. Obtained results are shown as the variation between the bearing capacity factor and considered parameters. It is found that with the increasing footing embedment, seismic bearing capacity increases considerably. The range of increment in the seismic bearing capacity of an embedded footing varies from seven to ten times that of no embedment. However, irrespective of footing embedment depth, the bearing capacity of footing reduces with increasing values of seismic acceleration coefficients. When both the horizontal and vertical seismic acceleration coefficients are considered together, seismic bearing capacity reduces more. However, it is also found that the footing bearing capacity is higher for soil with a higher damping ratio than that of the footing on a soil with a lower damping ratio. With increasing friction angle of soil, footing bearing capacity increases, but reduces with increasing slope inclination. State of stresses throughout the problem domain are plotted in the two-dimensional axes to understand the failure mechanism of slope under pseudo-dynamic loading. Results obtained from the study will be useful to the design engineers.

Random variability of strength and deformation parameters in soil mechanics is an indispensable attribute of naturally occurred soil deposits. Substantiation of the spatial and random variability of the parameters in soil mechanics is often carried out using results of some in situ tests. The implication of such randomness of parameters on design of shallow foundation has always been under scrutiny by experts in geotechnical engineering discipline. Plate load tests provide semi-continuous load-displacement profiles, which, when represented holistically, reap dividends that go far beyond the bearing capacity estimations. Different load-deformation models have been discussed in literature; however, provide a more realistic model, one needs to consider the physical concepts governing the limit load bearing capacity nature of soils. This study unfolds some uncharted territories of shallow foundation design in the realm of load and resistance factor design (LRFD). A hyperbolic load-deformation model, instead of the well-established power series model, is corroborated to represent the actual load-deformation behavior of natural soil deposits. To this end, some plate load tests, coupled with cone penetration tests (CPT), are invoked to establish a reliability based design (RBD) model, which enables serviceability limit state design of shallow foundations using Monte Carlo simulations. Finally, a load factor is proposed being predicated on the assumption of deterministic design approach. Results presented in this study can be directly implemented to shallow foundation design for both serviceability and ultimate limit states.