Journal of Geotechnical and Geoenvironmental Engineering

Existing approaches for the estimation of shaft and base resistances of drilled, cast-in-place piles have been compared on the basis of data collected from local geotechnical consultants, from load tests performed as part of foundation projects in Israel over the last decades. Three typical Israeli foundation soils were considered—clay, sand, and kurkar (partially and variably cemented sand). Data from 18 load tests at 13 sites were used for the study. Existing correlations were first used to estimate relevant soil properties from results of in-situ tests [usually standard penetration tests (SPT) or vane shear tests] performed during the project site investigations. These properties were then inserted in existing resistance estimation expressions. The resulting estimated resistances were compared to resistances indicated in the loading tests. A statistical analysis was used to choose the most reliable correlations and resistance estimation expressions for piles embedded in the various soils.

Temperature significantly affects the mechanical properties of geomaterials, particularly the creep behavior of soft clayey soils. Thus, an appropriate constitutive model to describe the time-dependent stress-strain behavior of clayey soils at various temperatures is necessary. This study performed temperature-controlled oedometer tests on two clayey soils: Hong Kong marine deposit (HKMD) and kaolinite clay (kaolin). The thermally-induced strain and creep strain rates under different temperature paths were investigated and discussed. A novel one-dimensional (1D) thermal elastic viscoplastic (TEVP) model was developed based on an existing 1D elasto viscoplastic (EVP) model. In the proposed model, the viscoplastic strain rate of soils can be described using three state variables: effective stress, strain, and temperature. The proposed model can be conveniently implemented in creep analysis with the equivalent time concept. The prediction results of the TEVP model were consistent with the experimental data for HKMD and kaolin.

This paper presents the results of research on soil erosion and its mitigation by different methods such as grass, riprap, lime, and enzymes. The goal was to evaluate these methods for their degree of efficacy using laboratory erosion testing. The paper begins with a review of existing knowledge on erosion mitigation methods. The erosion resistance of natural and improved soil was investigated in the erosion function apparatus (EFA), a laboratory device for measuring erosion resistance in the velocity range of 0.3 to $6.5\mathrm{m}/\mathrm{s}$. EFA testing was performed on grass-covered soils, riprap-covered soils, enzyme-treated soils, and lime-treated soils. The erodibility of the soils before and after treatment was compared. The results of the EFA tests were also compared with a few large-scale field tests available in the published literature. The advantages, limitations, and range of applications of each erosion mitigation method are provided.

In this study, the thermally induced changes in the shear characteristics of unbound granular materials (UGMs) were investigated. A series of drained shear tests were conducted using a large-scale triaxial apparatus under controlled temperatures. The thermal dependence of the peak strength, critical strength, internal friction angle, and dilatancy of UGMs were investigated under different temperatures, initial mean effective stresses, and relative compaction. Dense UGMs tended to expand during heating and slightly contract during cooling. In the heating and cooling process, a nonlinear relationship was observed between thermal deformation and temperature. Thermal deformation was attributed to the deformation, movement, and rotation of soil particles and closely related to the initial mean effective stress and relative compaction. A thermal softening effect was observed during the shear test, and the peak strength decreased with increasing temperature. However, negligible thermal effects were observed relative to residual strength. The effect of temperature on the shear characteristics of UGMs was primarily related to the thermal expansion of pores in the soil skeleton. The relationship between peak strength and initial thermal volumetric strain was found to be exponential. Considering the thermal effect, a normalized semi-empirical model of the parabolic Hvorslev envelope for dense UGMs was proposed to supply guidelines for road base design.

This paper discusses the instability of suction bucket foundations that are growing in importance for bottom-mounted offshore wind turbines in association with wave-induced liquefaction of sand beds. The instability of suction bucket foundations should be understood in light of fluid–soil–structure interactions. In this study, we investigated the instability using centrifuge wave testing in a drum channel with viscous scaling to match the time-scaling laws for fluid wave propagation and consolidation of the soil. This paper highlights the effects of loosening and heaving of the sand inside the bucket during the installation process, which is one of the onsite problems, on the overall stability and clarifies the stability of the whole system in light of wave–soil–structure interactions. The experimental results showed that the instability of the suction bucket is ascribed to the occurrence and progress of liquefaction of the sand bed around the bucket. The experimental results further demonstrated the effect of embedment of the bucket in a dense layer. An embedded depth of the bucket tip equal to one-third of the bucket skirt length prevented instability of the foundation, despite the spread of liquefaction in the loose sand bed. Even when the dense sand inside and underneath the bucket was loosened during the installation process, the foundation bucket remained stable against severe wave actions. The present study examined and summarized the overall stability of suction bucket foundations in sand beds under severe wave loading and clarified the importance of the progress of liquefaction around the foundations.

The steady-state shear strength of sands is affected by the physical properties of the sand. If the correlation between physical properties of sands and their steady-state strength is known, the steady-state strength can be obtained directly without mechanical experiments. Thus, the correlation has engineering significance for the prediction of liquefaction phenomena. This study explored the relationship between different physical properties and steady-state strength by conducting undrained triaxial compression tests on sands with different mean particle sizes, particle-size ranges, and fines contents. The results show that the steady-state strength of clean sands decreases with increasing mean particle size or particle-size range. The steady-state strength of nonplastic fines mixes is lowest when the fines contents is about 30% if their densities are the same, and increases gradually thereafter with increasing fines contents. When we used relative density instead of void ratio or dry density to evaluate steady state, the effects of grain size and its range of the host sand were diminished, whereas the effect of fines contents remained. On the other hand, when equivalent granular void ratio was used, the influence of fines contents ceased but the effects of grain-size distribution remained. In order to take advantage of both relative density and equivalent void ratio, the concept of the equivalent granular relative density is proposed, which is beneficial for evaluating the steady-state of sands with different physical characteristics, including the grain size and its range of host sand and fines content. The significance of this result is that the steady-state strength of various sands can be predicted to some extent from the density and grain-size distribution of the sand as well as the maximum and minimum densities of the host sand alone.

This study presents cyclic resistances of an instrumented medium dense sand (i.e., the Sand Array) and medium plastic silt (i.e., the Silt Array) deposit deduced from in situ dynamic testing using the controlled blasting test method. Particle velocity records were used to calculate the cyclic resistance ratios, CRRs, and convert the transient blast-induced ground motions into their equivalent number of shear stress cycles, $N_{eq}$, through consideration of the cyclic resistance observed from stress-controlled, constant–volume, cyclic direct simple shear (DSS) tests. The $CRR\text{-}{N}_{eq}$ relationship developed for the medium dense sand deposit demonstrated that the in situ cyclic resistance is larger than that (1) expected from cyclic DSS test specimens reconstituted to the in situ vertical effective stress, relative density, and shear wave velocity, $V_s$; and (2) calculated using case history-based, penetration-, and $V_s$-based deterministic formulations of liquefaction triggering models. Differences between the in situ cyclic resistance and that computed using probabilistic liquefaction triggering models reduced somewhat when considering probabilities of liquefaction exceeding 50% and 85%, depending on the model. Partial drainage during dynamic loading of the Sand Array appears to have contributed to the cyclic resistance of the sand deposit, with an increase of 6% to 27% compared to that estimated for fully undrained conditions. Differences between the cyclic failure criteria used to interpret the cyclic resistance of intact laboratory specimens of silt result in significantly different interpretations of the in situ CRR; the use of maximum excess pore pressure-consistent criteria appears to provide the best representation of the in situ, stress-based cyclic resistance when high quality, intact silt specimens form the basis for conversion of transient seismic waveforms to uniform shear stress loading cycles. The investigation described herein suggests that the reduction of cyclic resistance for plastic soils to account for multidirectional shaking ranges from 0% to 7% over $N_{eq}$ of 1 to 100.

A numerical study is presented of the effects of viscoplasticity on localization processes in sensitive, saturated clays and plastic silts. Numerical simulations of laboratory specimens of sensitive, viscoplastic soil subjected to monotonic, undrained, direct simple shear loading were performed using a viscoplastic constitutive model. Parametric analyses evaluated the effects of soil sensitivity, postpeak strain-softening rate, and strain rate dependency, as well as specimen size, mesh discretization, and loading rate. The numerical results showed that the global strain at which a localization forms primarily depends on the strain rate dependency of the soil’s shearing resistance relative to its rate of postpeak strain softening. A regression model is subsequently presented that relates the global strain at the onset of localization to the soil’s strain rate dependency and postpeak strain-softening rate. The results indicate that the inclusion of reasonable levels of viscoplasticity significantly increases the strain that can develop before a localization develops in clays and plastic silts with modest strain-softening rates. The consistency of the numerical results with available laboratory observations is discussed. Implications for practice and future research needs are discussed.

In this study, the thermomechanical response of the pile group and associated impacts on surrounding soil are explored numerically for different (1) layouts of energy and conventional piles, (2) soil types, and (3) pile spacing for the pile groups in Ottawa sand and Toyoura sand. The study outcomes demonstrate cyclic alterations in load–displacement characteristics of the piles and the soil during cyclic thermal loading and unloading of energy piles. Conventional piles exhibit uplift when energy piles are thermally loaded, with notable differential pile base displacement. Higher pile spacing results in decreased thermomechanical stresses in the piles. Compared with the middle energy pile in the same row, the corner energy pile experiences significant axial stresses. The radial stresses in the soil at the pile–soil contact increase due to the cyclic thermal expansion of energy piles. In addition, the layout of energy piles, pile location, soil type, and pile spacing control the load-transfer response of pile groups.

Soil strata delineation is a fundamental step for any geotechnical engineering design. The dynamic penetration test (DPT) is a fast, low cost in situ test that is commonly used to locate boundaries between strata of differing density and driving resistance. However, DPT data are often noisy and typically require time-consuming, manual interpretation. This paper investigates a probabilistic method that enables delineation of dissimilar soil strata (where each stratum is deemed to belong to different soil groups based on their particle size distribution) by processing DPT data with Bayesian changepoint detection methods. The accuracy of the proposed method is evaluated using DPT data from a real-world case study, which highlights the potential of the proposed method. This study provides a methodology for faster DPT-based soil strata delineation, which paves the way for more cost-effective geotechnical designs.