IFCEE 2021: From Traditional to Emerging Geotechnics

Natural period of structures can be elongated by the inclusion of a flexible foundation system. Period lengthening arising from the inclusion of soil–structure interaction (SSI) changes seismic design of structural and geotechnical systems, since period elongation may lead to larger demands in the structure. This paper parametrically studies the main variables that influence period lengthening characteristics of tall buildings. Variables such as the fixed-base natural period of buildings, structural aspect ratios, and effective soil shear wave velocity of supporting soils were included in the analysis using a direct approach. Three-dimensional (3D) numerical simulations including SSI effects were included to show the effects of period lengthening of tall buildings when compared to more common fixed-base 3D analyses. The analyses were performed using OpenSees by applying ground motions in two directions. Supporting soils are modeled by means of a direct approach in a fully coupled continuum soil-structure system formulation to represent in a more realistic manner the SSI effects. It is concluded that period lengthening of the first natural period of the structure arising from including SSI effects in the numerical framework produced more flexible structures. SSI generally increases the engineering demand parameters when compared to fixed-base models.

One-dimensional (1D) ground response analyses (GRAs) have generally been found to yield site response predictions that are different than recorded ground motions at many downhole array sites, presumably due to their laterally variable subsurface conditions. While there is no doubt that some sites are indeed too variable to be modeled using 1D GRAs, it is also possible that simple 1D analyses could still be effectively used if spatial variability is accounted for via a rational, site-specific approach. In this study, we test three approaches that can be used to account for spatial variability in 1D GRAs: (1) randomization of shear wave velocity (Vs) profiles; (2) increasing the small-strain damping ratio; and (3) an H/V geostatistical approach for generating site-specific spatially variable Vs profiles. We test these approaches at two downhole array sites so that the 1D GRA results can be compared with recorded ground motions. Of the investigated approaches, we find that the H/V geostatistical approach produces superior results and reproduces phenomena observed in the recorded site response at both downhole array sites. In regard to each of these approaches, we discuss issues that should be resolved to enable their adoption in practice.

Earthquake-triggered landslides have significant socio-economic impacts, claiming the lives of a third of the casualties associated with earthquakes due to their catastrophic runout. To improve the risk assessment and to mitigate the consequences of landslides due to seismic shaking, it is crucial to predict the initial triggering of mobilized mass (i.e., failure initiation) and to estimate the kinematics and postfailure final runout. While extensive work has been done in the field of earthquake engineering to address the small-strain failure initiation, the prediction of the kinematics and the final runout of earthquake-induced landslides have been less explored because of the complexities to simulate the shaking ground motion and the landslide event in a unified numerical framework. This paper presents the material point method (MPM) as a tool that is capable of simulating the landslide triggering and the whole instability process until its final runout. The use of a kinematic boundary condition applied to the nodes and a moving mesh technique is proposed to improve the efficiency of the calculation. A laboratory shaking table experiment is used for reference, and the MPM numerical results are compared to other nonlinear dynamic numerical approaches. Finally, a parametric analysis is conducted to understand the failure mechanics and emphasize the importance to further investigate the behavior of partially saturated soils subjected to dynamic loading.

In an urban area, during large earthquakes, a tall building will generate large base shear forces that may be transmitted into the underground structure through the building’s foundation and the surrounding soils. This study evaluates the impact of higher modes of the adjacent 13- and 42-degree of freedom (DOF) building models which represent 13-story midrise and 42-story high-rise buildings on the seismic response of the cut-and-cover tunnel in soil-superstructure-underground structure (SSUS) system using three-dimensional nonlinear finite element analysis. First, the seismic response of the tunnel adjacent to the equivalent 3-DOF midrise and 1-DOF high-rise models were compared to the corresponding centrifuge measurements, and good agreement was observed. Then, these calibrated numerical models are used to extend the building model into more realistic superstructure representation by including higher modes of the adjacent midrise and high-rise buildings. The results show that there is a significant increase in the spectral accelerations and base shear of the building due to the inclusion of the higher modes, which lead to the overall increase in dynamic earth pressure increments on the building-side wall of the tunnel. However, there are only small changes in the spectral accelerations and racking displacements on the tunnel wall. This study highlights that the seismic response of the building and tunnel might be underestimated if higher modes are ignored in the analysis.

The horizontal-to-vertical spectral ratio (HVSR) method has become an increasingly popular tool for developing a quick and reliable estimate of a site’s fundamental natural frequency (f₀). This paper presents HVSRweb, an open-source, web-based application for performing HVSR calculations in a convenient, reliable, and statistically consistent manner. HVSRweb allows the user to upload three-component ambient noise records and perform the HVSR calculation in the cloud, with no installation required. The HVSR calculation can be performed using a single combined horizontal component (e.g., geometric-mean, squared-average) or multiple rotated horizontal components to investigate azimuthal variability. HVSRweb can reject spurious time windows using an automated frequency-domain window-rejection algorithm, removing the need for subjective and time-consuming user interaction. It also facilitates the use of lognormal statistics for f₀, allowing for a consistent statistical framework capable of quantifying measurement uncertainty in terms of either frequency or its reciprocal, period. In addition, HVSRweb presents the opportunity to rapidly incorporate new developments in processing and quantification of uncertainty as they emerge and encourages standardization of HVSR processing across users while avoiding the challenges associated with traditional approaches that require the user to perform regular updates to keep pace with new developments.

In this paper, the liquefaction of saturated granular soil subjected to dynamic base excitation is evaluated using fully particle-based SPH-DEM approach, and the obtained results are compared to the results of pore-scale LBM-DEM technique. It is observed that the deposit liquefied during the application of strong base excitations as a result of reduction in porosity that led to pore pressure buildup and subsequent decrease of average particle coordination number and degradation of soil strength and stiffness. The comparison performed between the two methods also shows that the results of the computationally cheaper SPH-DEM approach are fairly consistent with the outcomes of highly accurate LBM-DEM technique.

Earthquake-induced liquefaction is always a concern when the soil near the surface of a site is composed of relatively loose saturated sand. One of the liquefaction mitigation methods is to induce gas bubbles into the deposit to reduce the degree of saturation. A coupled pore-scale model is presented herein to investigate liquefaction resistance of desaturated granular materials. The multiphase fluid, which mimics the behavior of air and water, is modeled using the multiphase single component lattice Boltzmann method. The solid phase is modeled using the discrete element method. The coupled framework is utilized to study the behavior of a soil deposit with gas bubbles-induced desaturation during an earthquake loading. Simulation results suggest that the risk of liquefaction effectively decreases with small reduction in the degree of saturation.

Coupled thermo-hydraulic-mechanical behavior of saturated porous media with low permeability is of crucial significance to operations such as thermal treatment for declogging wellbores and thermal fracturing during production of unconventional shale oil. This work presents coupled thermo-poroelastic solutions for an isotropic medium subjected to a constant fluid flux and a localized heat source, incorporating two novel components: (1) transient flow transfer between the source and the embedding layer; and (2) vertical confinement effects on the mechanical response of the target zone, governed by the stiffness of the sealing media using the Winkler model approximation. The Westerly Granite is selected to assess the thermo-poroelastic alterations induced under the imposed fluid flux and heat loads. Results reveal the thermal-fluid boundary condition to notably impact the response of the target zone. Stress path results near the source show the significance of incorporating vertical confinement when assessing the geomechanical response of the porous layer to fluid and heat sources.

The goal of this paper is to assess the effect of the temperature change rate on quasi-static thermally induced pore water pressure. Normally, consolidated clays subjected to elevated temperatures undergo thermally induced volumetric strains and thermally induced pore water pressures in drained and undrained conditions, respectively. The preliminary results of heating a normal consolidated clay in a partial single drainage condition show that the generation of the thermally induced pore water pressure is dependent on the temperature change rate; higher heating rates result in higher pore water pressures. Moreover, once the rate of thermally induced pore water pressure generation is equal to the rate of water dissipation, the generated pore water pressure remains constant as the maximum temperature is approached, i.e., reaching a quasi-static condition. In this paper, the effect of temperature change rate on quasi-static condition of thermally induced pore water pressure is evaluated.

The thermal conductivity of soil is an important property in the study of several emerging geotechnical and geoenvironmental engineering applications. In this study, a temperature-dependent model for the thermal conductivity function (TCF) of unsaturated soils is established by considering the effects of temperature on pore structure, water content, and heat transfer mechanisms. Most of the existing TCF models ignore the effects of temperature on pore structure and water content by treating the thermal conductivity only as a function of temperature and isothermal degree of saturation. To address these limitations, a new TCF model is developed by considering the effects of temperature on matric suction and the soil water retention curve (SWRC). The formulation for matric suction accounts for the effects of temperature on the surface tension, contact angle, adsorption, and enthalpy of immersion per unit area. The proposed model also applies a decay function to the degree of saturation to account for the thermal conductivity function affected by heat transfer phenomena such as conduction and convection of pore water in both liquid and vapor phases and latent heat transfer due to vaporization and condensation. A comparison between the results with experimental data obtained from the literature substantiates the validity of the model. The proposed model is used in a parametric study to examine changes in the thermal conductivity of a clay soil under temperatures ranging from 25°C to 100°C.

Coupled thermo-hydro-mechanical (THM) process in saturated porous media has been the subject of numerous studies. Recently, the influence of temperature gradient on the mass balance of fluid has been analyzed through the “thermo-osmosis effect” in low permeable soils, e.g., clay. In the case of thermal pore pressurization, the thermo-osmosis phenomenon causes the fluid flows away from the heat source and therefore alters the excess pore water pressure diffusion directly. Previous studies have shown that to better predict the thermal pressurization and thermal response of clayey soil, the thermo-osmosis phenomenon should be considered. Therefore, in the current study, a THM model with strong coupling is implemented in COMSOL multiphysics finite element software to assess the effect of thermo-osmotic flow in a saturated porous medium. The numerical results are compared with the experimental measurement of heating in Boom clay. The results show that thermo-osmotic flow leads to lower thermal pressurization in the vicinity of the heater; however, it does not affect the temperature distribution in the soil.

Vertical U-tube borehole heat exchangers (BHE) are commonly utilized to harvest shallow geothermal energy. As the BHEs are the most critical component, affecting the overall energy efficiency of ground source heat pump systems (GSHPs), it is essential to investigate the performance of BHE. In this study, the numerical modeling of a 132.5 m U-tube BHE employed for a geothermal heat pump de-icing system (GHDS) was investigated. Two numerical models were developed in COMSOL software to simulate the BHE operation accurately. First, the ground temperature file was simulated; then, it was used as the initial boundary condition for the second model, which simulated the BHE operations. Both numerical models were validated using field test data. Furthermore, sensitivity analysis has been performed on the validated thermal response test model for circulation fluid flow rate and thermal conductivity of the borehole grout. The results show that the increase in flow rate reduces the temperature difference between the inlet and outlet of BHE and increases the heat exchange rate. For example, an increase in the flow rate from 0.38 to 0.88 L/s boosted the average heat injection rate by 1.14 kW. Also, improving the thermal conductivity of borehole grout from 0.5 to 1.5 W/mK has caused 0.6 kW additional heat injection.

The scales on the underbelly skin of snakes can generate greater friction coefficients when they move forward than when they move backward. This property is referred to as frictional directionality and could be implemented to increase the efficiency of geotechnical applications such as deep foundations and soil reinforcement elements. To better understand the mechanism of frictional directionality, surfaces were idealized and manufactured based on 3D scans of snakeskin specimens. Previous studies with sandy soil have shown that snakeskin-inspired surfaces mobilized greater peak and residual friction and dilation angles during cranial shearing (i.e., soil moving against the scales) than during caudal shearing (i.e., soil moving along the scales). This paper presents the results of a study on the interface shear behavior of snakeskin-inspired surfaces with kaolin clay. The results of interface shear box tests indicate that shearing in the cranial direction mobilized greater interface strength than shearing in the caudal direction for tests performed at varying shearing rates, overburden stresses, and overconsolidation ratios (OCR). The results are compared with those from tests with a reference rough surface to highlight the differences in behavior resulting from the bio-inspired surface texture. A discussion is also included regarding the frictional anisotropy observed in both clayey and sandy soils.

Microbial-induced calcium carbonate precipitation (MICP) is evolving as a new method of improving the mechanical properties of soil. This environmentally friendly technique is a bio-geo-chemical process where microbes play a key role in increasing soil strength through precipitating calcium carbonate. Past studies at Boise State University have indicated that MICP via bio-stimulation could be a viable alternative for expansive clayey soil treatments. However, these studies raised a new question about the relationship between soil composition, urease activity, and calcite precipitation. To answer this question, batch studies were conducted using autoclaved-sterilized sand mixed with different percentages of non-sterile natural clay and tested for urease activity. Moreover, to investigate the difference in urease activity between sand and clay bacterial communities, experiments were repeated on samples with different amounts of non-sterile sand and autoclaved-sterilized clay. MICP-treated clay/sand mixes were then evaluated for calcite precipitation. Our results showed that soil mixes with higher clay content have more urease activity and higher levels of calcite precipitation for both sand-autoclaved and clay-autoclaved soil mixes. Test results indicate that urease activity could potentially be used as an indicator of MICP performance in different soil compositions.

This study aims to explore bio-inspired underground communication technologies and check the feasibility of using seismic waves for subterranean communication. It is known that some subterranean animals can convey and receive different information via seismic signals of different frequencies, amplitudes, and other characteristics. Inspired by subterranean animals, this study experimentally and theoretically studied seismic waves’ feasibility as an underground communication method. Experiments were conducted in the laboratory to analyze the performance of seismic waves as an information carrier. In the experiments, information (letters, numbers, and punctuations) was encoded and decoded using an on–off keying modulation method analogous to the Morse code. A parallel numerical simulation was conducted using FLAC3D, and its results fit qualitatively well with the experimental measurements. Numerical simulation and experiment results demonstrate that seismic waves can serve as a communicational information carrier, and the on–off keying modulation is a viable method to encode the signals.

In nature, seeds of some flowering plants such as Erodium and Pelargonium can bury themselves in the ground effectively and efficiently. This self-burial strategy has several key features: it is achieved by the hygroscopic coiling and uncoiling movement of the awn; the helical structure and movement induce net vertical penetration force; and the awns leverage anisotropic bristles to enhance the anchorage. In this study, another feature, namely the effect of rotation on penetration resistance, is studied using the discrete element method (DEM). A sudo-cylindrical (with a solid polygon cross section rather than a circular or helical one) was used to isolate the rotational effect. A series of rotational penetration tests were conducted with a set of calibrated microscale parameters from a previous study. It was observed that the rotational movement could reduce the penetration resistance. The reduction becomes significant at higher rotational speeds, but the corresponding power first decreases and then increases with the increase of rotational velocity, indicating the existence of an optimal condition. Further analysis of particle-probe contact forces unveils the underlying mechanism of the rotational effect on penetration. Specifically, rotation of the cone and shaft causes decrease in contact number and the vertical components of the particle-penetrator contact forces; in addition, the reduction of the contact normal force is more significant than that of the contact shear force.

An experiment to evaluate the use enzyme induced carbonate precipitation (EICP) for coastal erosion mitigation was conducted in the large wave flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University. The surface of a model sand dune was stabilized using EICP. The test slope was 7.2 m long, 1.8 m wide, and 1.5 m high (measured from the mean water level) and was composed of a local uniform fine beach sand. The slope surface was treated via EICP to form an approximately 5 cm-thick crust. In addition to crust formation, a 0.38 m-deep, 0.8 m in breadth zone at the toe of the slope was treated in lifts using EICP to form a toe wall across the 1.8 m width of the flume. The erosion resistance of the treated slope was tested by applying 20 wave trains of progressively increasing intensity. The crust remained intact for the first two wave trains and then progressively eroded until, at the end of the trials, the crust was completely eroded. However, portions of the toe wall remained intact at the end of the experiment and appear to have inhibited undercutting of the slope. The results of the experiment suggest that coastal erosion can be mitigated by construction of an EICP-stabilized toe wall to protect against undercutting of a slope and that it may be possible to construct a surficial EICP barrier of sufficient thickness to reduce slope erosion to a minimum, depending on the magnitude of the wave load.

All of us will never forget the year 2020. Those of us in higher education will perhaps reflect on the Spring 2020 semester as a turning point in our approach to education. To prepare higher education for future crises and to create a more buoyant, elastic, and resilient educational paradigm, it is imperative that we learn, right now, from the COVID-19 crisis. This is of particular importance for engineering education, which relies on experiential pedagogical practices that are incongruent with online learning environments. Since 2014, a multi-institutional interdisciplinary team has been addressing improvements to engineering education through mixed reality gaming, an educational model that integrates traditional classroom experiences (e.g., lectures, laboratory work) with virtual activities (e.g., game-based learning). We posit that a mixed reality gaming educational model may help mitigate the impact COVID-19-like crises. Herein, we reflect on implementations of a mixed-reality gaming activity in an introductory geotechnical engineering course on five campuses during the pivot to remote learning, which will be remembered as the hallmark of the Spring 2020 semester. Ultimately, the data gathered from these implementations will be used to study the effectiveness of mixed reality gaming on student learning outcomes (specifically, the ways in which student and instructor motivation shape and are shaped by this educational model) to understand (1) the role of mixed reality gaming; and (2) instructors’ and students’ motivational shifts during such crises.

Contemporary social and policy themes were integrated in undergraduate classroom activities in two separate investigations: (1) a collaboration between a civil engineering computer programming laboratory course and microbiology lecture/laboratory course; and (2) a stand-alone activity in a geotechnical engineering laboratory course. In both cases, a contemporary theme related to climate change was selected. For the civil engineering/microbiology collaboration, synchronous and asynchronous interactions between lower division students were facilitated for policy initiative of diverting food waste from landfills. For the geotechnical engineering laboratory, the theme related to the connection between power transmission infrastructure and wildfires in California. The interdisciplinary collaborative activity resulted in incorporating research components into curriculum and led to students pursuing research investigations. The new geotechnical laboratory exercise engaged the students more than the conventional tests and resulted in higher technical performance and cognitive achievements. Guidelines are provided for implementation of the activities.

Earthen levees are critical flood protection infrastructure consisting primarily of earthen masses to retain water and secure the landside area against flooding. However, many earthen levees are located in the active seismic zone. Thus, it is critical to evaluate the reliability of earthen levees in the face of earthquake hazards, since the failure of such structures can be catastrophic and cause loss of lives, damages to properties, and significant adverse economic and societal impacts. This paper presents a simplified probabilistic assessment framework for earthen levees under earthquake loads. In this framework, the pseudo-static method with the finite element analyses is used for the stability analyses of earthen levees under earthquake loads. The pseudo-static method uses a static horizontally applied load to simulate the effect of an earthquake on the earthen structure. Then, the probabilistic assessment is conducted using an efficient reliability method that accounts for propagation of uncertainties from the input random variables through the finite element modeling. The effects of acceleration level on the probability of failure of earthen levees are quantified. The developed framework provides an efficient tool for probabilistic evaluation of earthen levees that is easy-to-use by practicing engineers. The results can help engineers to make a risk-informed decision in the face of earthquake hazards. A case study is utilized to demonstrate the effectiveness of the proposed framework for the reliability assessment of earthen levees under earthquake loads.

Although located in the Great Plains, over 24,000 slope failures have been observed in North Dakota. These failures present a number of issues including blocking roads, damaging pavements, and posing numerous safety concerns. A geospatial database of these slope failures is presented in this study. The database is used to examine the geologic, topographic, and pore fluid salinity patterns at these slope failures. The majority of slope failures occur in the Sentinel Butte Formation, which primarily covers the western part of the state. McKenzie and Billings Counties contained the largest number of slope failures accounting for 21% and 14%, respectively, of the total. Approximately 6% of the slope failures have areas larger than 100,000 m², nearly 23% have areas between 2,100 and 6,100 m², and 0.1% have areas less than 100 m². Slope failures appear to concentrate in relatively gentle slopes with inclinations between 8° and 12°. Additionally, the majority of the failures were in soils with low salt concentrations in the pore fluid, which is notable since the presence of high salt concentrations in soils is considered nearly ubiquitous across most of North Dakota.

Rainfall-induced slope failure is one of the major maintenance problems for highway slopes constructed on high plasticity clay in subtropical humid areas. Due to the infiltration of rainwater, the topsoil loses its matric suction, resulting in unsaturated shear strength reduction and making the slope vulnerable. Since the recycled plastic pin (RPP) is considered an alternative cost-effective and quick method for repairing shallow slope failures, the aim of this study is to investigate the performance of the RPP to stabilize shallow slope failure under rainfall events. A parametric study using the finite element method (for seepage analysis) and the limit equilibrium method (for slope stability analysis) was conducted to examine the effect of rainfall events on a slope located at U.S. Highway 287, in Midlothian, TX. Field monitored suction contour was used to replicate the initial field steady-state flow condition. Then, transient flow analyses were conducted by applying rainfall events with different intensities and duration. The calculated pore-water pressure profile from transient seepage analysis was then used for the slope stability analyses. The results indicate that the long-time low-intensity rainfall events significantly reduce the stability of the unreinforced slope by critically decreasing the factor of safety. In contrast, the slope stabilized with RPPs is found to be effectively holding the slope during rainfall events of different intensity and duration.

In this study, three-dimensional (3D) model tests and numerical analyses were conducted to investigate the pull-out behavior of a tunnel-type anchorage for suspension bridges. Special emphasis was placed on evaluating the failure modes of the tunnel-type anchorage. The comparison results of the failure modes on the anchorage showed that the numerical results were in good agreement with the model test results. Therefore, the applicability of the numerical solutions was confirmed for the evaluation of the pull-out behavior of tunnel-type anchorages. Based on the results of the model tests and the numerical simulations, the failure mode of the tunnel-type anchorage was shown to be plug and wedge-shaped failure that depended on the relationship between the length of the anchor plate and the diameter of the anchorage body.

This paper presents the failure heights and failure modes of eight column-supported embankment (CSE) scenarios as determined from three-dimensional finite difference analyses. CSEs were supported by unreinforced concrete columns with properties representative of vibro-concrete. Scenarios consisted of a base case using typical column design and a layer of geosynthetic in the load transfer platform, single-parameter variations using base case conditions, and multiparameter variations using base case conditions in which the simultaneous change in multiple parameters resulted in a significantly worse or better condition than the base case. Selected parameters are important for design and site characterization (i.e., column spacing and diameter, geosynthetic tensile capacity, and clay’s undrained shear strength). At different embankment heights, equilibrium was computed for an undrained state in which excess pore water pressures have developed in the clay and for a long-term state in which the excess pore water pressures have fully dissipated. The failure height was defined as the embankment height at which deformations continually increased in either the undrained or dissipated condition. Columns and geosynthetic reinforcement were each assigned a failure criterion. Key findings are as follows: (1) CSE stability is most critical at undrained end-of-construction; (2) embankment failure height is significantly influenced by the clay’s undrained shear strength; (3) two failure modes were found, and both involve complex soil column interactions and flexural tensile failure of the unreinforced concrete columns; and (4) if a geosynthetic is included in design, then collapse occurs in the undrained condition after geosynthetic tensile failure. Implications for practice are discussed.

Tropical cyclones are common to islands in western Pacific including Guam, and they bring large amounts of rainfall within a short duration, thereby triggering landslides. It is well understood that accurate modeling of the response of the hillslope to shallow landslides resulting from heavy rainfall in mountainous basins requires consideration of unsaturated soil mechanics principles. In this study, soil was collected from shallow depths along slopes of a reservoir in southern Guam, and soil water retention curves (SWRC) were obtained in the laboratory. Furthermore, results are presented from transient seepage analyses coupled with limit equilibrium method-based slope stability analyses on a typical slope. Comparison of results with and without a rainfall event captures the sudden drop in matric suction and factor of safety of the slope due to infiltration, which confirms that storm events are the leading cause of landslides in hillslopes located in tropical environmental settings.

Three-dimensional (3D) probabilistic slope stability analysis using limit equilibrium methods is a time-consuming procedure. Using traditional sampling methods such as Monte Carlo or Latin hypercube may take days of computation, especially when there are multiple random variables and complicated geometries involved. Stochastic response surface (SRS) method is a very fast and effective approach for probabilistic analysis of 3D complicated geometries, which reduces the number of simulations and simulation time dramatically. The SRS method uses a small number of samples that cover the parameter space to train the model. Any number of samples can then be plugged into this model and will result in the estimated factor of safety values for each sample. In this study, an SRS algorithm using third-order Hermite polynomial expansion that works effectively for complex 3D probabilistic analysis is presented to show the performance of this method in the probabilistic analysis. A complex open pit model with several random variables has been investigated using the SRS method, and the results are compared with Latin hypercube simulation results. The results using both methods are in good agreement. However, the SRS method computation time was about 7% of that of the Latin hypercube computation.

Embankments built using high-plasticity clayey soils often demonstrate shrink-swell behavior due to changes in moisture regime due to the alternating dry-wet seasons. The increase in temperature causes excessive evaporation and drying of soil to the extent that it may induce desiccation cracks in clayey soils, whereas precipitation causes a drastic reduction in soil suction, which decreases the soil strength. Additionally, precipitation on desiccated slopes may induce shallow slope failures, which may lead to significant damages. Recent climate change observations have indicated an increase in extreme weather conditions. Therefore, it is important to study the effects of extreme weather conditions on various civil infrastructure assets including embankments. The objective of this study is to assess the impact of future extreme precipitation events on the stability of embankment slopes. The study considered historical extreme precipitation events as a baseline to quantify the effects of future extreme precipitation. For this, the historical and future precipitation data were obtained for a study area located in North Texas. Future precipitation data were obtained from the Coupled Model Intercomparison Project, version 5 simulations. A combination of a finite element-based software for seepage analysis and limit equilibrium-based software for slope stability analysis was used in this study. The findings of this study indicate that the future extreme precipitation may reduce the factor of safety against embankment slope stability failure in the North Texas region.

Reinforced concrete cantilever retaining wall (CRW) with predetermined height and backfill slope is designed using a reliability-based optimization. FORM is applied to calculate the reliability index and to estimate the failure probability of the cantilever reinforced retaining wall. The formulation for computing the system reliability index incorporates six global stability limit state functions pertaining to different modes of failure in addition to 14 internal strength limit states. The uncertainties in the properties of backfill soil, foundation soil, retaining wall materials, and dimensions are modeled as random variables following suitable probability distribution functions. The analysis also takes into account the established correlation between different random variables. An RBO (reliability-based optimization) is then applied to determine the optimal design parameters. The design optimization is calibrated to a target reliability index that is acceptable by the related code standards.

A technique of statistical design of experiments (DoE) is combined with finite element (FE) analysis to evaluate the strength reduction factor (SRF) sensitivity to slope geometry and soil properties such as slope height (H), the slope angle of inclination (β), friction angle (ϕ'), cohesion (c’ or c), elastic modulus (E), Poisson’s ratio (υ), pore water coefficient (r_u), and unit weight (γ). The analysis is conducted by performing two-dimensional FE analysis in a central composite design fashion classifying the soil into three groups: purely cohesive (c, undrained analysis), purely frictional (ϕ'), and mixed soils (c’ and ϕ'). The findings indicate that for the mixed soils, six main coefficients (c', β, r_u, ϕ', γ, H) and their interactions have significant effects on the response. For the purely cohesive soils, c, H, β, and their interactions have larger effects on SRF. For purely frictional soils, the larger positive effect comes from ϕ', and the large negative effects come from β, r_u, and their interactions. Based on the results, recommendations for achieving optimum stabilization techniques for each soil group are given.

Numerous well-known buildings have experienced differential settlement throughout history and various efforts to rectify these tilted structures were developed and presented in the past. Structural differential settlement is typically mitigated by increasing settlement of the lower settlement areas (balancing settlement methods) or by jacking the more settled area (uplifting methods). However, new methods are constantly being researched to reduce construction time, mitigation cost, risk, and service disruptions. The intent of this study is to propose, evaluate, and analyze a new technique for rectifying tilted structures which can address some of these concerns. The proposed method harnesses slurry shield microtunneling boring machine (MTBM) technology as a modern underexcavation technique for balancing settlement. The effectiveness and adequacy of this method were investigated with numerical analyses which are presented in this paper. Valuable design application information for designers, owners, and/or contractors that seek to apply this methodology is also provided.

Florida’s unique geology poses multiple engineering concerns when characterizing the subsurface conditions in both previously and newly developed landscapes. Florida’s covered-karst landscape has ushered the seemingly never-ending-battle between the propagating population and karst’s consequential sinkhole geohazard. The cone penetration test (CPT) has been widely used for subsurface investigations in covered-karst landscapes due to the test’s ability to provide a nearly continuous profile of soil resistance, allowing engineers to precisely determine the depths in which internal soil erosion may have taken place. However, once these conditions are identified, there still lacks a viable assessment technique which is both reproducible site-to-site and verified to quantify the location’s vulnerability to future sinkhole collapse. In this paper, the authors review a database of 26 project sites located in Florida where CPTs were performed to investigate the potential of sinkhole activity. Within the 26 project sites, a total of 155 CPTs were performed in and around the identified sinkhole occurrence (either collapse or depression). Using statistical correlation and categorical regression of the location of CPT to the proximity to sinkhole feature, an empirical function was developed relating the location’s vulnerability for sinkhole development to various CPT-obtained subsurface condition variables. The resulting empirical function can then be used as a relative estimation of sinkhole vulnerability when performing CPTs within karst project sites in Florida. When multiple CPTs are performed within an identified karst anomaly, the proposed assessment index can be calculated for each and compared against a proposed criterion for better discernment of mitigation strategies.

Detailed information of soil/rock properties and associated spatial variability is crucial for the successful design and construction of deep foundations. Traditional invasive methods such as standard penetration test (SPT) and cone penetrometer test (CPT) only sample a small volume of soil and rock material at the testing site. Surface-based geophysical methods can provide overall subsurface conditions but are limited to shallow depths due to reflections of surface source energy from stiffer underlying material. To address this issue, we present a novel SPT-seismic method for deep site characterization. Seismic waves generated by SPT spoon (traditional N-value) at various depths are recorded by a 2D grid of geophones on the ground surface and analyzed by a 3D full-waveform inversion (3D FWI) to extract subsurface material properties. A field experimental trial (soil over rock) was conducted to provide new insights into its utility as a viable geophysical tool for deep site characterization. Not only were 3D S-wave and P-wave velocities of subsurface soil and rock within 9 m around the SPT boring well characterized, but also a deep void (15-m depth) away from the boring was identified within the rock. S-wave velocity values of the final inverted result are also compared with SPT N-values, and a good overall agreement over the whole depth is observed.

Geo-slicing is a novel in situ sampling technique developed in Japan to identify evidence of paleoseismicity in soil deposits not conducive to trenching. To preserve and enhance the stratigraphic features of the geo-slice sample, a “peel” is created from the vertical slice of the soil profile by laying a reinforcing cloth and a grout or adhesive over the slice. After the adhesive dries, the cloth is removed from the slice. A thin layer of soil remains attached to the cloth, creating the peel. The peel can then be examined for paleoliquefaction features such as dikes and sills of sand that are generally devoid of bedding structures. Previous geo-slicing studies used a highly toxic Japanese grout. To conform to modern environmental regulations, it is necessary to identify a less-hazardous grout that still produces a satisfactory peel. A bench-scale study of multiple adhesives for creating geo-slice peels was performed. Adhesives are evaluated for their efficacy in creating a relief that enhances the bedding structures of the soil slice and for other properties such as flexibility and hazard level. Of the eleven adhesives evaluated herein, flex seal liquid was identified as most suitable for creating geo-slice peels.

Final cover system for landfill closure is one of the most significant components of a landfill. Recently, water balance cover systems, also referred to as evapotranspiration (ET) cover for landfill closure, have gained notable consideration by landfill operators due to its effective long-term performance. The hydrological performance of ET covers, fundamentally, depends on the field hydraulic behavior [i.e., saturated (K_s) and unsaturated (K_Ψ) hydraulic conductivity, soil water characteristic curves (SWCC)] of the soil. Hence, field measurements of K_s and K_Ψ are important to have thorough understanding of the field hydrological processes for performance evaluation. Unlike the saturated hydraulic conductivity (K_s), measurement of K_Ψ in the field is challenging, and there are limited data of K_Ψ for water balance cover systems. The objective of this paper is to evaluate the field unsaturated hydraulic conductivity of instrumented water balance cover (lysimeter) test sections at the City of Denton landfill, Texas. Six lysimeters were constructed at the site using local fine-grained soil (CH), framing 12.2 × 12.2 × 1.22 m in dimensions. Moisture sensors and tensiometers were installed at each of the lysimeters at specified depths. Field-based SWCC were developed from the co-located sensors, and the instantaneous profile method (IPM) was used for the field measurement of K_Ψ. Field measured data sets were compared with two of the popular models; the van Genuchten–Mualem (VM) and the Brooks–Corey (BC) model. Based on the analysis from the instrumentation data, K_Ψ ranged between approximately 10^-4 and 10^-12 cm/s. The upper limit of the permeability value (10^-4 cm/s) nearly represented the saturated hydraulic conductivity in the field. The BC model slightly overestimated the field measurement, whereas the VM model closely resembled the field condition.

Being able to accurately identify the rippability of rock materials is essential for many civil engineering projects that involve rock excavation. The current procedure for rock rippability estimations using geophysics is solely based on the P-wave velocity of the rock. However, with the increased use of multichannel analysis of surface waves (MASW) for performing pseudo 2D V_s surveys, the need for V_s rippability charts continues to increase. This study develops new rippability charts based on rock V_s. To do so, Poisson’s ratios of different rock formations are first determined using downhole measurements and laboratory testing on rock core samples. The results are then compared to examine the limitations of laboratory testing as a common practice for rock Poisson’s ratio estimation. It was observed that in situ Poisson’s ratios of rock formations are often underestimated using laboratory measurements. This is because laboratory testing is conducted on a small sample of intact rock, which is not a true representative of the in situ rock conditions. The results clearly indicate the need to account for such underestimation in the rock Poisson’s ratio when using laboratory measurements. Finally, using the Poisson’s ratios from downhole measurements, updated rock rippability ranges are determined based on V_s. These charts can be used along with any field methods that measure V_s of subsurface materials to estimate rock rippability.

In this study, we carry out lab-scale 1D electrical resistivity measurements of frost-susceptible clayey sands, focusing on several major influencing factors including initial water content, soil density, temperature, and freezing/thawing conditions. Soil columns are configured following a four-pole type Wenner electrode array and placed in an environmental chamber to reach target temperatures (–20°C to 0°C). We use a portable resistivity meter for temporal electrical resistivity measurements and thermocouples for temperature measurements. Experimental results highlight the significant dependence of soil electrical resistivity on temperature. Above the freezing point, higher initial liquid water content and larger bulk density decrease the electrical resistivity. Below the freezing point, soil resistivity increases with decreasing temperature. We observe a hysteresis effect on the evolution of electrical resistivity during the freeze thaw cycle. This study presents a relationship between the electrical resistivity of frozen soil and the key governing parameters.

This study examines the ability of the multichannel analysis of surface waves (MASW) method to accurately recover the size, stiffness, and depth of subsurface anomalies. The dispersion data considered in this paper were derived from waveforms generated using two-dimensional (2D) finite-difference elastic wave-propagation simulations. These simulations were performed to replicate a typical MASW field experiment on models with and without subsurface anomalies, referred to as “treatment” and “control” models, respectively. In a previously published study, the treatment and control models were compared exclusively based on differences between their experimental dispersion data to determine whether or not the anomaly could likely be detected. This study examines whether those models previously categorized as containing a detectable anomaly, based on their experimental dispersion data, can be inverted to accurately resolve the anomaly’s size, stiffness, and depth. To rigorously perform the inversions, we adopt the procedures recommended by the surface wave inversion workflow SWinvert, which involves using multiple large-scale global-search inversions to address the problem’s nonlinearity and multiple layering parameterizations to address the problem’s nonuniqueness. Following the inversion process, the shear wave velocity (Vs) profiles from the single “best” model associated with each layering parameterization are compared to the one-dimensional (1D) Vs profile from the centerline of the true model using an error function to quantitatively assess the ability of the MASW method to accurately resolve subsurface anomalies. Intuitively, the ability to resolve subsurface anomalies is shown to improve as the anomaly is moved closer to the ground surface and its lateral extent increases. Surprisingly, however, in this study anomalies with lateral extents less than approximately ½ the array length located at depths >5 m most likely cannot be resolved accurately by using MASW, even when the anomalies are relatively thick (>2 m) and the impedance contrasts are notably high (>2).

The response of a shallow foundation is significantly influenced by the uncertainties associated with not only the geotechnical parameters but also the hydrological parameters that include rainfall intensity and duration, drought intensity and duration, and groundwater depth. These hydrological parameters alter the strength and deformation properties of the subsurface soil resulting in variation in foundation performance. This paper presents a mathematical framework to optimize the performance of shallow foundation subjected to site-specific hydrological loads with respect to the uncertainties associated with site-specific geotechnical and hydrological parameters. In the proposed framework, the shallow foundation design is performed based on partially saturated soil mechanics principles, and the optimization is performed using a multiobjective optimization algorithm called nondominated sorting genetic algorithm (NSGA-II). The results of this study show that the proposed method can improve not only the performance of the foundation but also reduce the total construction cost.

The current practice in designing the foundation for the onshore wind turbines (WT) relies on the use of rotational stiffness to size the foundation such that the serviceability requirements are met. A rotational stiffness is considered acceptable if it provides the right boundary (foundation) rigidity to ensure a non-amplified dynamic response of the WT. The common method used to verify acceptable foundation performance is through direct measurements of applied moment due to wind loading and direct measurement of tilt. The accuracy of the tilt measurements is questionable due to the small tilt magnitude, and the required high frequency of tilt measurements. This paper presents an alternative method to evaluate foundation stiffness from the dynamic response of the WT by estimating the WT fundamental frequency (f_n). Numerical model is then calibrated by changing the boundary rigidity until the f_n from the model matches the f_n obtained from the WT dynamic response. The rigidity from the calibrated numerical model is then compared to the design intent for the foundation, which allows for the evaluation of the foundation performance.

Pinnacle bedrock topography presents major challenges when evaluating the design length of deep foundation systems. Such topography is formed in rocks prone to dissolution by acidic ground water. Typical subsurface characterization techniques with drilling, standard penetration testing (SPT), and cone-penetration testing (CPT) may fail to adequately map the true design elevation of competent bedrock due to the spatially limited extent of these measurements. Surface wave geophysical methods such as the multichannel analysis of surface waves (MASW) can potentially address this limitation, but the current analytical approaches suffer from limited resolution and spatial averaging. In this study, a full waveform tomographic approach is proposed to evaluate bedrock topography using surface wave measurements. Seismic wave propagation was numerically simulated at a representative site with dipping pinnacle bedrock topography. The resulting waveforms were processed using a dispersion-based MASW approach as well as a full waveform inversion (FWI) tomographic approach. The results from this numerical study demonstrated that the FWI approach for surface wave analysis offered superior spatial resolution and coverage compared to conventional MASW and was better able to identify dipping pinnacles in the bedrock that could prove problematic when selecting an appropriate foundation design elevation. Further studies, especially field experiments, are necessary to make a generalized conclusion.