Journal of Geotechnical and Geoenvironmental Engineering

Particle-scale mechanisms that control the static creep behavior of crushable sands are not well understood. In this context, this study examines the problem of creep of crushable sands undergoing one-dimensional (1D) compression by using a three-dimensional (3D) discrete element method (DEM) simulation. The rate process theory (RPT)-based creep contact model considering rolling resistance and a probabilistic particle fracture model satisfying mass conservation were incorporated into a large-scale DEM simulation. The coupled effects of the interparticle sliding and delayed particle fracture and the influences of rolling resistance, initial porosity, and characteristic particle strength on the creep behavior were then investigated. The high capabilities of the model in reproducing many facets of the soil behavior during the 1D compression and creep seen in the laboratory was demonstrated by comparing the simulation results with published experimental data. It was found that the creep deformation was mainly caused by stress redistribution at low vertical stress while particle rearrangement and particle breakage became more prevailing with the increase of vertical stress.

This paper presents one-dimensional ground response simulations of centrifuge models involving soft clay deposits subjected to ground motions of varying intensity. Total stress ground response simulations were performed using equivalent-linear (EL) and nonlinear (NL) methods. Shear strains higher than 10% were mobilized during large ground motions; therefore, undrained shear strength of the clay is an important parameter for the simulations. Testing shows that the San Francisco Bay Mud materials used in centrifuge modeling have monotonic shear strengths that increase by 13% per log cycle of shear strain rate. A comparison of simulation results to observations reveals the importance of incorporating shear strength into the development of stress-strain backbone curves, with appropriate consideration of rate adjustments to shear strength and stiffness. NL ground response simulations provide a good match to observed pseudospectral accelerations only when rate-adjusted shear strengths are properly accounted for; otherwise, the NL simulations have significant underprediction bias at oscillator periods less than the soil column period. EL modeling, even with the incorporation of shear strength, leads to unrealistic spectral shapes and overprediction at short spectral periods for tests involving large-strain site response.

To investigate the seismic earth pressure on a shallow foundation, a dynamic centrifuge test using a sinusoidal sweep motion was performed on a superstructure–footing model embedded in dry sand deposits. The resultant seismic earth pressure and vertical wall friction acting on the plates on the active and passive sides were separately measured using two-dimensional load cells. The shapes of the measured hysteresis loops of earth pressure and relative displacement varied with the input motion period. The amplitude of the earth pressure depended on the mobilized wall friction angle rather than on the soil acceleration. A key factor for the hysteresis-loop shape was the phase difference between a peak of the mobilized wall friction angle and that of the relative displacement. The mobilized wall friction angles were dependent on the overturning moment caused by the superstructure inertia. When the relative displacement was mainly caused by the soil displacement, the phase between the relative displacement and the wall friction angle could be large. The earth pressure did not peak at a peak in the relative displacement.

The paper offers an analytical solution for radial consolidation that captures isotaches with a strain-rate dependency of preconsolidation pressure. These relationships are obtained based on constant-rate-of-strain (CRS) and long-term consolidation (LTC) tests and then used in the radial consolidation model incorporating the field strain rate, which is generally much lower compared with the typical laboratory environment. In this study, the calculated settlement and associated excess pore-water pressure are obtained using the equivalent preconsolidation pressure from the reference isotache within the $({\sigma }_p^{\prime }/{\sigma }_{p0}^{\prime })-(\dot{{\epsilon }_v})$ domain. Moreover, the change in $C_{\alpha }/C_c$ ratio (i.e., secondary compression index/compression index) with decreasing strain rate is used to calculate the long-term settlement. This method is then validated using various case histories in Australia and Southeast Asia, where excess pore-water pressure is dissipated at a slower rate in relation to the observed settlement.

Hysteretic soil water retention behavior is the key information required for interpreting and predicting the hydromechanical responses of unsaturated soils during drying and wetting processes. For this reason, models capable of describing such behavior are valuable in the development of constitutive relationships for unsaturated soils. In this paper, a model is proposed for predicting the main and scanning soil-water characteristic curves (SWCCs) (degree of saturation-suction relationships). In addition, the model is extended to another model for predicting the main and scanning soil-water characteristic surfaces (SWCSs) (degree of saturation-void ratio-suction relationships). The proposed models need one extra parameter ($q$ for SWCC or $q^{\prime }$ for SWCS), in addition to parameters required for conventional SWCC or SWCS models. The major advantages of the proposed models are as follows: (1) measurements of the main drying and wetting curves or surfaces are the only information required to calibrate all model parameters, (2) model predictions allow a smooth transition from scanning curves or surfaces to the main curves or surfaces, and (3) calibration associated with the parameter $q$ or $q^{\prime }$ can be further refined using measurements of scanning curves or surfaces to improve the precision of the predictions. The performance of both proposed models was validated against measurements of six different soils ranging from sands to clayey soils. Reasonable agreements between predictions of the proposed models and experimental results are achieved for all soils investigated in this study.

The effect of preshaking and repeated liquefaction on liquefaction resistance was studied in a large-scale shaking table experiment, in which a sequence of 51 shakings was applied to the base of a 5-m uniform deposit of saturated clean Ottawa sand. Three event types were used in a very intense repeated pattern: mild preshaking Events A, stronger preshaking Events B, and extensive liquefaction Events C, with each Event C typically liquefying most or all of the deposit. Relative density, cone penetration test (CPT) tip resistance, and liquefaction resistance to Events A and B were found to increase significantly throughout the 51-shaking sequence, with the shear wave velocity ($V_s$) increasing slightly. However, the CPT tip resistance and liquefaction resistance decreased temporarily after each Event C, recovering rapidly with additional preshaking—presumably due to a decrease and subsequent increase in the soil lateral stresses. The results for the different shakings were compared with available CPT- and $V_s$-based field liquefaction charts, with and without accounting for the fact that the soil deposit was much younger than the case histories covered by the charts (age factor). The liquefaction response for Events A, B, and C was reasonably well predicted by the CPT chart when the age factor was considered, including Events A immediately after liquefaction by an Event C. The implications of the research were discussed for the geologic age, preshaking and liquefaction effects observed in the field, including reliquefaction response of the same site by milder aftershocks after the main earthquake shock.

The effects of daily cyclic temperature variations on the thermal response of an energy pile built under a six-level residential building are examined. The axial and radial thermal strains along the length of the pile followed stable, linear reversible paths during daily active heating and cooling cycles corresponding to a pile temperature range of 10°C to 23°C ($\mathrm{\Delta }T$ of $-8°\mathrm{C}$ to 5°C) around a baseline temperature of 18°C. The stable responses of the thermal strains indicate that plastic deformations did not occur in the pile during the daily cyclic temperature changes coupled with the mechanical load in the pile corresponding to 52% of its estimated ultimate capacity. A complex distribution of axial thermal stresses with depth was observed in the pile, with higher stress magnitudes near the pile ends particularly at the end of cooling because of larger temperature changes in the cooling cycle. The magnitudes of radial thermal stresses were considerably smaller than the axial thermal stresses along the length of the pile and are not anticipated to play a significant role in the development of thermomechanical loads in the pile. The temperatures over the cross section of the pile were uniformly distributed at the end of cooling and heating at all depths, while the axial thermal stresses had a nonuniform distribution but with magnitudes less than the calculated ultimate capacity of the pile.

An effective stress limit plasticity solution developed at the Norwegian Institute of Technology (NTH) provides a theoretical evaluation of the effective stress friction angle (${\varphi }^{\prime }$) for soft to firm normally consolidated (NC) to lightly overconsolidated clays (LOC) from piezocone penetrometer tests (CPTu). A modified NTH method using the equivalent stress concept is detailed to allow the evaluation of effective stress friction angle for overconsolidated (OC) clays. The solution requires a knowledge of the soil stress history, specifically, the overconsolidation ratio (OCR). A wide variety of clays have now been calibrated using this approach, including measured CPTu and triaxial data collected from six categories: (1) laboratory chamber tests in NC clays; (2) centrifuge testing in NC clays; (3) centrifuge tests in OC clays; (4) field CPTu in natural NC-LOC clays; (5) field CPTu in OC intact clays with $\mathrm{OCR}>2.5$; and (6) field CPTu in OC fissured clays. Results from compiled databases are statistically shown to validate the CPTu-interpreted ${\varphi }^{\prime }$ values in comparison with laboratory benchmark values obtained from CAUC and CIUC triaxial tests made on high quality samples. Case studies of CPTu soundings conducted in the aforementioned categories are presented to elaborate the application of the NTH solution.

The effects of sand fabric anisotropy on the response of vertically loaded rigid strip footings were numerically investigated with the use of a bounding surface constitutive model developed within the premises of anisotropic critical state theory. In agreement with pertinent centrifuge test results that were successfully simulated, this paper showed that if the strip footing rests on a sand with a horizontal deposition plane, smaller footing settlements, higher bearing capacity and a wider and deeper failure mechanism are observed, compared with those that appear if the same sand (at the same relative density) has its deposition plane rotated to the vertical direction. Anatomy of the experimentally verified numerical analyses revealed that these differences in footing response are governed mostly by the anisotropic behavior of the sand located under the footing, which is significantly stiffer and more dilative under vertical load when its deposition plane is horizontal rather than vertical. Regardless of initial fabric anisotropy, the development of a distinct failure mechanism is progressive and requires significantly more footing settlement than that for the ultimate (maximum) bearing capacity. In practice, neglecting fabric anisotropy effects may lead to significant overestimation of the ultimate bearing capacity of footings on sand.

Although a number of cutoff walls have been built in dams with alluvial foundations, the produced wall response still requires further understanding. This paper focuses on the comparative study of responses of cutoff walls on the basis of comparative analysis and numerical simulation. The present study first gathered a database of 58 cases describing the performance of concrete cutoff walls. The loading characteristics, typical deformation pattern, and deformation response of the walls installed at different locations were reviewed from a comparative point of view based on case histories. The effects of several factors on the wall response were discussed. A three-dimensional (3D) finite-element deformation analysis was conducted to provide further understanding of the response of cutoff walls and the mechanisms that affect their response. The mechanical response, damage distribution, and cracking of the concrete cutoff wall located in the upstream face of the dam were analyzed and compared with those of walls located at the middle of the base of the dam fill. The numerical results for the mechanical responses of the wall were also compared with the in situ measurements and comparative results to verify the validity of the numerical model.

A multitude of mechanisms will affect the evolution of the pile response over time, each with their respective time scale. It is shown that most of the processes can be linked to the pile installation stage, which alters the soil surrounding the pile. As a result, there is a change in the mechanical properties of the soil that will influence the subsequent pile response over time. These long-term mechanisms include the dissipation of excess pore pressures from pile installation and the creep in the soil. This paper presents a numerical approach that combines the strain-path method, an advanced effective stress–based constitutive model for soft soils, and a multiphase numerical framework that enables the modeling of the pile installation and subsequent change of pile bearing capacity over time. The presented results demonstrate that the degree of remolding of the soil during the pile installation stage is closely linked to the subsequent pile response. For the Onsøy test case studied, the increase in shaft capacity over time, demonstrated to be linked to undrained strength recovery, could be faithfully reproduced during and after dissipation of excess pore pressures. Hence, pile aging of displacement piles installed in clay is strongly linked to installation effects and the creep and relaxation processes in the soil. Further study is required to fully reveal the physicochemical mechanisms that underpin these processes.

Hydraulic conductivity tests were conducted on two commercially available bentonite–polymer composite (BPC) geosynthetic clay liners (GCLs) containing the same dry blend of sodium bentonite (NaB) and polymer sandwiched between two nonwoven geotextiles (GTs) bound by needlepunching: a bentonite–polymer GCL (BP GCL) and bentonite–polymer GCL with silt film (BPS GCL). The GCLs were essentially identical except that the BPS GCL contained a woven slit-film GT to constrain polymer elution. The slit-film GT was located inside the GCL adjacent to the downstream nonwoven GT. The test liquids were deionized (DI) water and 20–500 mM ${\mathrm{CaCl}}_2$ representing dilute to high-concentration permeant solutions. Effluent from the hydraulic conductivity tests was analyzed for total organic carbon (TOC) to quantify polymer elution. Scanning electron microscopy (SEM) was used to capture how the solution chemistry affected the fabric of the BPC and how hydraulic conductivity was related to pore-scale features in the fabric. Both BPC GCLs were approximately one to four orders of magnitude less permeable than a conventional NaB GCL permeated with the same solutions. Polymer elution data and SEM images of polymer structure suggest that polymer retention in the pore space and pore clogging by polymer hydrogel are responsible for the lower hydraulic conductivity of BPC GCLs. The BPS GCL had less polymer elution and hydraulic conductivity three orders of magnitude lower than the BP GCLs when permeated with 50 and 100 mM ${\mathrm{CaCl}}_2$ solutions because the slit-film GT reduced polymer elution from the bentonite. A conceptual framework is proposed relating solution chemistry, pore-scale fabric, and hydraulic conductivity of dry-blended BPC GCLs.

Mechanistic approaches to developing cone penetration test-based liquefaction triggering correlations are presented and evaluated with an application to Ottawa sand. The mechanistic approaches utilize combinations of data from undrained cyclic direct simple shear tests, dynamic geotechnical centrifuge tests with in-flight cone penetration profiles, and cone penetration simulations. Cyclic direct simple shear tests on Ottawa sand characterize the relationship between cyclic resistance ratio ($CRR$) and relative density ($D_R$). Relationships between cone tip resistance ($q_c$) and $D_R$ are developed from geotechnical centrifuge tests and cone penetration simulations. Penetration simulations using the MIT-S1 constitutive model with three different calibrations for Ottawa sand examine the role of critical state line shape and position on simulated $q_c$ values. The $CRR-D_R$ relationship from laboratory tests is composed with measured and simulated $q_C-D_R$ relationships via common $D_R$ values to develop $CRR-q_c$ relationships. An alternative $CRR-q_c$ relationship is developed from inverse analyses of centrifuge test sensor array data (i.e., arrays of accelerometers and pore pressure sensors). The results of these different approaches are compared to case history–based correlations for clean sand and their relative merits discussed. Recommendations are provided for future application of these mechanistic approaches to developing liquefaction-triggering correlations of poorly characterized or unique soils.

The hyperbolic $p-y$ curve method is commonly used to design laterally loaded piles. The initial stiffness ($K$) and the ultimate resistance per pile length ($p_u$) are the two key parameters that are required to determine the hyperbolic $p-y$ curve. Multiple competing models are available for determining the term $K$, which makes it difficult for the designer to select a proper initial stiffness model. Six existing initial stiffness models are assessed and compared from the robust design perspective in this paper. Specifically, a framework based on the concept of robust design is proposed for assessing these initial stiffness models considering multiple objectives such as safety, cost, and design robustness. This framework is illustrated with an example, the design of a laterally loaded pile in clay using the $p-y$ curve method. Based on the outcome of this example study, the most preferred initial stiffness model for the laterally loaded pile design is suggested. To enhance applicability, the proposed framework based on the robust design concept is simplified and illustrated with a spreadsheet solution.

Load transfer across soil–structure interfaces plays an important role in the capacity and efficiency of many geotechnical applications. Some geotechnical applications may benefit from soil–structure interfaces that mobilize different amounts of shear resistances depending on the direction of loading. Bioinspiration is used in this study to develop a series of surfaces modeled after the ventral scales of different snake species that exhibit anisotropic interface shear behavior. The frictional behavior of the snakeskin-inspired surfaces was assessed by means of interface shear box tests on sand specimens composed of two different sands. The results indicate a prevalent anisotropic behavior, where shearing in the cranial direction (i.e., against the scales) mobilized larger peak and residual interface strength and dilation than shearing in the caudal direction (i.e., along the scales). A parametric study on the geometrical characteristics of the scales revealed the isolated effect of their height and length, and particle image velocimetry analyses revealed larger soil deformations and dilation induced within the soil during cranial shearing. The scale geometry ratio is shown to qualitatively capture the interface load-transfer mechanisms between the sand and different bioinspired surfaces.

A helical pile is composed of a steel shaft and single or multiple helical plates welded to its shaft. This study investigated full-scale seismic soil reactions for helical piles embedded in dry sand. Ten helical and driven piles were installed in sand enclosed in a laminar shear box mounted on a large outdoor shake table. The paper discusses interpretation of the seismic loading data and the derived dynamic $p\text{-}y$ curves. It examined different curve-fitting formulations utilized for interpretation of pile deformation and soil reactions from measured strains during the tests. An optimum curve-fitting function was selected considering the current test setup and was used to establish soil resistance along the pile shaft and the corresponding $p\text{-}y$ curves under simulated earthquake records. The influences of loading frequency, loading intensity, installation method, number of helices, shaft shape, and coupling type on the dynamic $p\text{-}y$ curves were evaluated. It was found that the loading frequency and intensity had no effect on the dynamic $p\text{-}y$ curves, whereas the installation method, number of helices, and pile shaft shape had minor effects on the obtained dynamic $p\text{-}y$ curves.

In earthquake-prone areas, risk analyses of seismic potential failure modes for embankment dams are often required. In order to evaluate these potential failure modes, seismically induced deformations are needed. The use of numerical modeling to determine embankment dam deformations has gained wide attention in practice, especially when involving liquefiable soils. This study presents a validation assessment of a finite-difference computer program using embankment dam prototypes tested in dynamic centrifuges. Similar to the total-stress analysis methodology, undrained shear strengths were used to characterize seismic behaviors of the embankment soils. As a simplified approach, uncoupled modeling with a primitive constitutive model was adopted. Quasi-steady-state strengths were determined from the laboratory stress-strain curves for the dilative soils tested in the centrifuges. Calculated results were found to be comparable with the measured data from the centrifuge experiments, which provides some level of confidence in the predictive capability of the finite-difference computer program. In particular, a good correlation was observed between the $v_{\max }/a_{\max }$ ratio of the seismic input motions and the calculated settlements.

The soil stress state is three-dimensional (3D) in many applications, including the case of traffic loading. This aspect has been rarely undertaken in the laboratory. This paper investigates the one-way cyclic behavior of a reconstituted saturated clay based on a true triaxial apparatus, considering the factors of cyclic stress ratio (CSR), coefficient of cyclic intermediate principal stress ($b_{\mathrm{cyc}}$), and overconsolidation ratio (OCR). Emphasis is put on the effects of these factors on the behavior of major principal strain, intermediate principal strain, and resilient modulus in the direction of major principal stress. The results indicate that the development rate of major principal strain is reduced greatly by increasing $b_{\mathrm{cyc}}$, and the direction of intermediate principal strain is changed from negative to positive. The resilient modulus is increased significantly and almost linearly by the increase of $b_{\mathrm{cyc}}$. The relationships of major principal strain, intermediate principal strain, and resilient modulus against CSR all show that one-way cyclic shakedown behavior of saturated clay is independent of OCR and can be determined by $b_{\mathrm{cyc}}$. A specific cyclic stress boundary ratio, i.e., the allowable cyclic stress ratio, which was proposed for soft clays as a reference of deformation control under traffic loading, is determined as 0.347, 0.364, and 0.394 from the tests under $b_{\mathrm{cyc}}=0$, 0.4, and 0.8, respectively.

The lateral performance of large-capacity helical piles is of significant interest. This study presents the results of five full-scale lateral load tests conducted on 6.0 and 9.0 m large-capacity helical piles of shaft diameter 324 mm and installed in structured cohesive soil. The piles were either single or double helix, with inter-helix spacing of 1.5 and 3.0 times the helix diameter, instrumented with strain gauges. The shorter piles were tested under a short-term condition, whereas longer piles were tested under a long-term condition. The soil’s $p\text{-}y$ curves and its initial modulus of subgrade reaction were back calculated from the strain measurements and were compared with the subgrade modulus estimated from the properties of the undisturbed soils. The pile installation had a significant effect on the subgrade modulus. The number of helices and the inter-helix spacing ratio had minimal influence on the mobilized load deflection at pile head and soil resistances. A reduction factor for the initial subgrade modulus was introduced to be incorporated in design.

Geotechnical centrifuge tests were conducted to examine the behavior of low-aspect-ratio piles and caissons in clayey soils subject to high moment loading. Model piles with an aspect ratio of two were tested in the 150g-t centrifuge at Rensselaer Polytechnic Institute. Results include moment-inclination and force-displacement response for different loading conditions. Numerical studies were also performed consisting of three-dimensional finite-element simulations in order to predict capacities. The comparisons are performed in terms of the total resistance exerted by the soil on the caisson. This paper focuses on presenting the ultimate bearing capacity factors, including both experimental and numerical results. In addition, results are compared to a series of studies available in the literature, which include upper-bound solutions and experimental results.

Four large laminar-box shaking table experiments are conducted to document pile response due to the mechanism of liquefaction-induced lateral spreading. Single-pile and pile-group configurations are tested in a mildly inclined ground configuration. Two ground profiles of about 5 m in height are investigated, one with a liquefiable saturated sand stratum and the second with an added upper crust. The recorded data sets from this series of experiments are analyzed collectively to document and track the evolution of lateral loading on the deployed pile and pile-group configurations. Ground and pile lateral displacement as well as excess pore pressure are discussed. In this series of tests, it is observed that some of the highest pile lateral loads occur at the initial stages of lateral deformation, as the excess pore pressures approach the level of liquefaction. Thereafter, lateral load might decrease with further shear strength reduction and deformation in the liquefied stratum. For such soil profiles, lateral ground deformation that continues to accumulate due to the shaking process may not always result in significantly larger loads on the embedded pile foundation.

Understanding the soil resistance along an embedded anchor chain is imperative for efficient and economic design of an overall mooring system as it determines the magnitude and direction of the load at the padeye of the anchor. The tensioning process of an embedded chain for catenary moorings was modeled using a coupled Eulerian–Lagrangian (CEL) finite-element approach simulating the large deformations of the chain as it cuts through the soil to form an inverse catenary. The analyses reveal that the configuration of the embedded chain and the relationship between tension and chain angle at the padeye show excellent agreement with previously published analytical predictions. However, the ratio of the tension at the padeye to that at the mudline obtained from CEL is significantly higher than the theoretical values, mainly due to partial mobilization of the frictional soil resistance along the length of the chain. The CEL results indicate that the partial mobilization is a result of the combined-loading effect during failure of the soil around the embedded chain as it cuts through the seabed, in contrast with the conventional assumption that the ultimate frictional and normal soil resistances are mobilized simultaneously. A new design approach is proposed for calculating the local equivalent coefficient of friction based on the yield locus for a deeply embedded chain and the normality rule.

Undrained shear strength is one of the most commonly used geotechnical design parameters for fine-grained soils. Disturbance produced during boring, sampling, and testing introduces an often unquantified and variable bias into undrained shear strength measurements, which in turn introduces bias and uncertainty into geotechnical design. Evaluations performed to quantify variability and bias in undrained shear strength determined using five different sampling and testing methods are described. The variability of undrained shear strength measurements differs considerably among sites, but is generally least for isotropically consolidated-undrained triaxial compression (CIUC) tests performed on high-quality specimens, slightly greater for unconsolidated-undrained triaxial compression (UU) tests performed on high-quality specimens, and greatest for unconfined compression (UC) tests performed on lesser-quality specimens and pocket penetrometer (PP) and handheld torvane (TV) tests. Quantitative bias determined for different sampling and testing methods is generally consistent with conventional wisdom regarding sampling and testing quality. The minimum achievable uncertainty for undrained shear strength is controlled by uncertain bias; coefficients of variation representing uncertainty are likely to be greater than 0.25 if sampling and testing methods that are inappropriate for a specific design application are used. Evaluations presented also suggest site-specific testing for shear strength parameters using stress history and normalized soil engineering properties (SHANSEP) techniques may reduce variability and uncertainty by approximately 10%–40% compared with using empirical estimates.

Column-supported embankments (CSEs) with or without a load-transfer platform (LTP) can reduce settlements, improve stability, and prevent damage to adjacent facilities when embankments are constructed on ground that would otherwise be too weak or compressible to support the new load. CSEs function by transferring the embankment load to the columns through stress redistribution above and below the foundation subgrade level. Mobilization of load-transfer mechanisms to the columns requires differential settlement at the base of the embankment between the stiff columns and foundation soils. This paper presents the load-displacement compatibility (LDC) analysis method, which estimates the transfer of vertical loads by (1) arching within the embankment fill, (2) the vertical component of tension developed in the geosynthetic reinforcement within the LTP, and (3) negative skin friction acting along the column. The LDC method incorporates the vertical displacements that accompany load transfer by considering nonlinear consolidation of the soft foundation soil, elastic compression of the columns, out-of-plane deformation of geosynthetic layers, and settlement of the embankment surface in compliance with the differential settlement at the embankment base. This paper also presents recommendations for estimating the critical height of the embankment, which is the minimum embankment height above the columns to avoid poor ride quality resulting from differential settlement at the surface of the embankment produced by differential settlements at the base of the embankment. Estimates of load transfer and reinforcement strain using the LDC method are compared to measurements from 15 full-scale embankments.

A set of saturated Ottawa sand models was treated with microbially induced calcite precipitation (MICP) and subjected to repeated shaking events using the 1-m radius centrifuge at the UC Davis Center for Geotechnical Modeling. Centrifuge models were constructed to initial relative densities ($D_{R0}$) of approximately 38% and treated to light, moderate, and heavy levels of cementation (calcium carbonate contents by mass of approximately 0.8%, 1.4%, and 2.2%, respectively) as indicated by shear wave velocities ($\mathrm{light}\approx 200\mathrm{m}/\mathrm{s}$, $\mathrm{moderate}\approx 325\mathrm{m}/\mathrm{s}$, and $\mathrm{heavy}\approx 600\mathrm{m}/\mathrm{s}$). The cemented centrifuge models were compared to a pair of uncemented saturated Ottawa sand models with initial $D_{R0}\approx 38$ and 53% and subjected to similar levels of shaking. Cone penetration resistances and shear wave velocities were monitored throughout shaking to investigate (1) the effect of cementation on cone penetration resistance, shear wave velocity, and cyclic resistance to liquefaction triggering; and (2) the effect of shaking on cementation degradation. Accelerometers, pore pressure transducers, and a linear potentiometer were used to monitor the effect of cementation on liquefaction triggering and consequences. Cone penetration resistances and shear wave velocities were sensitive to light, moderate, and heavy levels of cementation (increases in penetration resistance from 2 to 5 MPa, from 2 to 10 MPa, and from 2 to 18 MPa and increases in shear wave velocity from 140 to $200\mathrm{m}/\mathrm{s}$, from 140 to $325\mathrm{m}/\mathrm{s}$, and from 140 to $660\mathrm{m}/\mathrm{s}$, respectively), and were able to capture the effects of cementation degradation.

During installation of a skirted foundation, resistance to penetration is a combination of side and tip resistances. When penetrating a permeable soil unit, tip resistance in particular can be high but if seepage water flow from the outside to the inside of the skirted foundation exists, the pore water gradient will reduce the effective stresses and therefore also penetration resistance. Recent installation data from the field and laboratory suggest that this effect can also occur during installation in layered profiles. This paper presents a model that accounts for seepage flow in unlimited permeable layers that are overlain by one or several impermeable layers. The model assumes that seepage flow in the underlying sand layer is induced by an incremental lift of the internal soil plug, which enables the transfer of some of the differential pressure applied under the foundation lid to the bottom of the lifted soil plug. A single equation is proposed to calculate the critical suction number for layered soil conditions that can be used with an empirical model to calculate the reduction in penetration resistance. A calibration of the proposed equation for the critical suction number is carried out using an axis symmetrical finite-element model that uses a linear elastic soil model and assumes steady-state flow conditions. The calibration of the proposed equation for calculating the critical suction number was first carried out for a homogenous permeable soil. This was done to benchmark the model against previously published data. In a second step, the calibration was done for a layered profile and different flow boundary conditions. The proposed penetration model is demonstrated by back-calculating full-scale installations. The paper closes with a discussion of the main assumption of plug lift, and a simple model to evaluate the degree of plug lift is proposed.

Offshore wind turbines supported on jacket structures are subject to many cycles of axial loading due to wind and waves, which may densify the soil around the piles and decrease the lateral stress on the soil-pile interface. Static axial loads may cause dilation of adjacent soil and increase the lateral stress. Results from model tests have demonstrated the potential for increases and decreases in pile stiffness, capacity, and pullout rate depending on the combination of static and cyclic loads, but the fundamental mechanisms are not fully understood; a one-dimensional, axisymmetric finite-element model is developed to investigate these mechanisms. The Dafalias-Manzari bounding surface plasticity model is used for the soil. Downward shear and cavity expansion at the pile interface are used to simulate installation, which is followed by the application of static tension and cyclic loads. Static tension causes initial contraction of near-pile soil, followed by dilation if the tensile load is further increased. Presence of a moderate static tension results in increased stiffness initially in one-way cyclic loading. With additional cycling, overall contraction in the far field leads to reduction of lateral stress and localized dilation (loosening) at the interface. Furthermore, if the cyclic loads cause small plastic deformations, however small, the numerical model suggests that tension piles would eventually pull out. Limitations of the numerical model are critically assessed.

Several short-duration and extreme hydraulic loadings impose time-dependent variably saturated seepage conditions on earthen slopes and embankments. Difficulty assigning appropriate input parameters and lack of full-scale validation are among the main factors introducing uncertainty and lack of confidence when performing numerical transient seepage analysis. This case study demonstrates how to effectively use field-monitoring data to improve the numerical analysis of a levee under climatic and tidal variations. The case study includes a silty sand setback levee located near Seattle. An array of tensiometers and soil moisture sensors installed within the levee’s embankment and foundation, along with a nearly real-time data acquisition system, were used to collect and process the in situ data for a period of about 15 months. Climatic and weather data, including precipitation, temperature, humidity, and wind speed, were collected from a weather station at the site, and tidal water fluctuations were monitored using a water level sensor. The field-measured matric suction and water content were used along with a suction stress–based representation of effective stress to compute suction stress and effective stress profiles versus time. A finite-element model of transient seepage under saturated-unsaturated conditions was developed. The numerical model was calibrated and then validated using the measured pore-water pressures and the piezometric surface. The application of the numerical model was illustrated by modeling the seepage and stability of the levee during a 100-year flood event. The results highlight the need to consider climatic variables and soil–atmosphere interaction when performing transient seepage analysis.

This study presents the results of interface torsional ring shear tests conducted at intermediate normal stress levels that are usually prevalent at soil–pipeline interfaces under near-shore conditions. Four normally consolidated soils of different plasticity and five solid surfaces with diverse roughness were utilized in this single-stage shear testing program. The drained peak and residual soil and interface shear strengths were measured and compared with the relevant data available in literature. The analyses and interpretation of the study results revealed that the drained peak and residual interface efficiencies (i.e., the ratio between soil and interface friction angles) are almost equal. These efficiencies can be estimated using one simple correlation that is valid regardless of the effective normal stress range. The correlation helps in the preliminary estimation of pipe–fine-grained soil shearing resistance when the beta (or effective stress) approach is adopted.

The usage of soil-cement reinforced layers to bear shallow foundations is a viable option in low-bearing-capacity soils. Existing methodologies that can determine the bearing capacity in such cases tend to consider the cemented layer’s bounds to be infinite, depending solely on the ratio between the footing width and the layer’s thickness. The present study intends to assess the influence of the reinforcement width on the load-settlement behavior of a circular steel footing resting on square-edge soil-cement layers bearing on a weak highly porous residual soil. Static load tests were carried out on footings (diameter of 300 mm) resting on sand-cement reinforced layers with distinct areas (edges of 450, 600, and 900 mm) and constant thickness of 300 mm. The results have shown two distinct failure modes that rely on the cemented layer’s width. A punching mechanism was observed for the two smaller reinforcement’s layers and they did not fail. The 900-mm square cemented layer, on the other hand, had a failure that was initiated by the formation of tensile cracks and fissures in the center of its bottommost segment. This study highlights the importance of considering the soil-cement layer’s width in the bearing capacity estimation of footings resting on treated layers above weak cohesive-frictional soils.