Journal of Geotechnical and Geoenvironmental Engineering

Field observations of semitaut mooring systems have shown severe trench development in front of suction caissons. Trenches extend back from where the chain emerges from the seabed under ambient mooring loads to relatively close to the caisson and with depths approaching the padeye depth. To help understand the process, a coupled Eulerian–Lagrangian (CEL) approach has been used to apply cyclic loading to a mooring chain system, treating the chain as a series of linked cylindrical elements and the soil as a strain-softening Tresca material. The chain extended through the soil into the water column, and cyclically changing boundary conditions were applied to the far end of the chain to reflect a typical mooring layout and metocean conditions. Despite rather idealized conditions, with loading restricted to the vertical plane of the chain and no consideration of hydrodynamic effects, a stable trench profile developed after only a few cycles of loading. The chain profile straightened during the cycles, with the section nearest to the padeye gradually cutting deeper into the soil and with the amplitude of cyclic motions of the chain, and hence tendency for a trench to form, increasing at shallower depths. The magnitude of soil resistance acting on the chain reduced by increasing cycles, with particularly low resistance in the zone where the trench was most developed. The long-term longitudinal profile of trenching was predicted based on the current modeling and was found comparable to that inferred from field observations, even without consideration of hydrodynamic and out-of-plane effects.

Cyclic softening of fine-grained soils poses a significant hazard to geotechnical infrastructure in many parts of the world. Methods to numerically evaluate the cyclic softening and subsequent localization behavior in clays in practice are less developed than techniques to model liquefaction-induced strength loss of granular soils. The PM4Silt constitutive model can model the dynamic response of low-plasticity silts and clays while being relatively easy to calibrate and use. This paper investigates the ability of PM4Silt to model earthquake-induced deformations caused by strain-softening of a mildly sensitive clay. The Fourth Avenue landslide that occurred in Anchorage, initiated by the 1964 Great Alaska Earthquake, is used in this evaluation. Results from previous studies are used to estimate site stratigraphy and relevant soil properties. The model calibration procedures and results are discussed. Simulation results using PM4Silt are compared with the observed displacements and results from previous studies using different constitutive models. The effects of different model calibrations are studied, as well as the influence of input motion and mesh density. The results demonstrate the PM4Silt is able to capture the general response of the Fourth Avenue landslide, although the results are sensitive to the input parameters and show some dependency on mesh size.

This paper presents a practical analytical approach to evaluating the long-term and set-up shaft resistance of prebored piles. The key contributions of this study lie in the fact that not only all aspects involved, from pile installation to pile loading, but also the residual stress propagated from the vertically shearing effect during pile installation are properly considered in the proposed analytical approach. The installation effects of a prebored pile are simulated as undrained expansion of a cylindrical cavity followed by vertically shearing the soils along the boundary of the pile shaft. To develop the possible analytical approximation technique, simplified solutions for the stress and excess pore pressure changes in critical sate soils due to cavity expansion are adopted in the formulations, while a modified Terzaghi’s consolidation theory that incorporates a variable coefficient of consolidation with respect to the void ratio and mean effective stress of the soil is employed to model the consolidation process after the pile installation. The proposed analytical approach has been well validated through comparisons with a finite-element numerical model that involves the entire process from pile installation to loading. The approximate analytical model developed in this work, owing to its relative formulation simplicity, computational efficiency, and prediction reliability, is expected to be able to serve as a feasible analysis method and guidance for the design and construction of piles involving the preboring procedure.

Cement-admixed soil columns are often used to strengthen the surrounding soft soil for enhancing tunnel stability. Such improved soil surrounds possess high spatial variability and heterogeneity in the strength and stiffness properties. In this paper, three-dimensional random finite-element analysis is conducted to compute the equivalent strength and stiffness for tunnels constructed in overlapping cement-admixed soil columns surrounded by soft clays. The heterogeneity and spatial variability of the improved soil surround are studied by varying coefficient of variation, considering anisotropic scale of fluctuation in mean strength and stiffness, as well as varying positioning error arising due to the off-verticality in cement-treated columns. Finally, strength reduction factors are computed for obtaining the equivalent strength of tunnels in such spatially variable improved soils. The proposed range of strength reduction factors can be used in numerical analysis by engineers in practice to compute the appropriate values of equivalent strength and stiffness of homogeneous improved soil surrounds around tunnels. The influence of varying permeability of improved soil surround and time of excavation of tunnel opening on the equivalent strength is also studied and was not found to be significant.

Retaining walls mechanically stabilized with reinforcement frequently have proven their resilience while maintaining an advantage over conventional (gravity and cantilever) walls in terms of cost effectiveness and environmental impact. To achieve optimized design beyond the inherently conservative code specifications, reliable pullout models are needed. The paper enriches the existing literature with results from a series of laboratory pullout tests involving inextensible steel grid reinforcement (in the form of bar mat) embedded in dense sand. Comparative tests were used to determine the role in key response mechanisms of parameters such as the reinforcement width and the spacing of longitudinal and transverse elements. The dominant role of soil dilatancy was identified and its effect on the response of different grid configurations was interpreted by recourse to simple conceptual physical models. It was found that interference between zones of restrained dilatancy may be substantial enough to promote the use of coarser (and hence more economical) mesh configurations, especially at shallow depths. For the pullout factor in highly dilative soils, a closed-form expression is proposed which describes reasonably well the experimental results, and adequately captures the interrelated phenomena occuring in two directions, transverse and longitudinal.

The shaft capacity of foundations highly depends on the monotonic and cyclic loads applied to the soil–structure interface. In energy geostructures that exploit the heat of soil using earth-contact elements, the interface is subject to cyclic thermomechanical loads. Monotonic and cyclic constant-volume equivalent-undrained (CVEU) direct shear tests were performed on clay–clay and clay–structure interfaces at different temperatures (22°C and 60°C). An effective vertical stress of 300 kPa was applied to the samples and the cyclic and average shear stress ratios (${\tau }_{cy}/S_u^{Ds}$ and ${\tau }_a/S_u^{Ds}$, respectively) were varied between 0.35 and 0.57. The tested soil was a kaolin clay (plasticity $\mathrm{index}=24$) prepared in a normally consolidated state. The results showed that the number of cycles to failure for the clay–structure interface test was lower than that for the clay–clay case in the same range of cyclic and average shear stress ratios. In cyclic clay–structure tests, decreasing the cyclic stress ratio increased the number of cycles to failure; however, decreasing the average shear stress ratio decreased the number of cycles to failure. Increasing the temperature decreased the rate of strain accumulation, and the number of cycles to failure increased by two to three times. The rate of degradation (degradation parameter, $t$) decreased by 16% with heating from 22°C to 60°C for the different cyclic stress ratios tested.

Climatic conditions easily allow for volume change of expansive soils. This happens due to the wetting and drying cycles that affect the moisture active zone. The suction compression index (${\gamma }_h$) is the key parameter that relates volumetric changes to soil suction changes in unsaturated soils. It is defined as the slope of the suction–volumetric strain relationship. This relationship is essentially nonlinear and the slope is determined for an idealized form of the relationship. Therefore, the need for a precise ${\gamma }_h$ determination method has always been in demand. The more accurate ${\gamma }_h$ is determined, the more accurate soil movements can be predicted and taken care of early in the design stage of a project. Accordingly, more money can be saved from either the repair costs or the initial costs by avoiding overdesign. The purpose of this paper is to introduce an original testing method for ${\gamma }_h$ determination. The testing method uniquely incorporates volumetric and suction measurements in a new and practical way utilizing simple digital imaging. The testing method unprecedentedly integrates statistical modeling for determination of incremental ${\gamma }_h$ in order to cover the entire nonlinearity of the suction–volumetric strain relationship. This is done by fitting the S-shaped relationship by a well-known class of statistical functions called cumulative distribution functions (CDFs). Incremental ${\gamma }_h$ is estimated by estimating the CDF at every suction value. The appropriateness of using these estimates to describe the suction–volumetric strain relationship is evaluated using the Kolmogorov–Smirnov (K–S) goodness of fit test. Furthermore, 95% confidence intervals of the superposed curves are also used to assess the appropriateness of the CDF estimates. The new testing method is compared against other techniques in the literature and proven reliable results.

The deep vertical bearing capacity of rectangular foundations of varying aspect ratios (0.2–10) are explored within a coupled Eulerian–Lagrangian (CEL) finite element modeling framework. The CEL model is verified against existing numerical and theoretical solutions. For accurate shallow bearing capacity assessment, large deformation finite element (LDFE) solutions were found to be suitable if penetration resistance is extracted at normalized penetration depths of less than 5% of the foundation width. The deep bearing capacity factor for a circular foundation was predicted within $\sim 2\%$ for a smooth foundation and $\sim 5\%$ for a rough foundation. Soil weight and stiffness were found to have no impact on the penetration resistance at shallow depths but to influence the resistance at deeper depths. The relative foundation thickness has a profound influence on the deep bearing capacity factor (${\mathit{N}}_{\mathit{c}}$). Increasing the normalized foundation thickness from 0.1 to 0.5 increased the bearing factor by more than 20%. An alternate soil flow mechanism was discovered responsible for this increase. The deep bearing capacity factor for a rectangular foundation was found to nonlinearly increase with the footing aspect ratio. An exponential form of equation was shown to capture well the effects of varying aspect ratio and footing thickness. The effect of the common assumption of a rigid foundation on bearing capacity in geotechnical numerical analyses has been revisited.

Accurate modeling and prediction of the variation of the hydraulic conductivity of unsaturated soils at a very low degree of saturation has important implications in various engineering problems. Physical processes underlying the hydraulic behavior of unsaturated soils (retention behavior and variation of hydraulic conductivity) are first explained, and then a consistent set of new definitions for key transition hydraulic states is proposed. This lays the foundation for the presentation of a new predictive hydraulic conductivity model, accurate for the full range of degree of saturation and applicable to relatively coarse-grained soils (i.e., gravels, sands, and silts). The hydraulic conductivity is divided into two components—a bulk water component and a liquid film component—each of which varies with the degree of saturation or suction. The model is then validated against experimental data. Finally, the new hydraulic conductivity model is applied to the numerical study of the hydraulic behavior of capillary barrier systems (CBSs). The new model is able to predict the behavior of CBSs better than conventional models, and the numerical modeling highlights the role of liquid film flow, which is often neglected.

This paper presents and interprets experimental results of soil–reinforcement interaction tests conducted using a new device developed to assess the mechanical interaction among neighboring reinforcements in geosynthetic-reinforced soil masses. Testing involved a soil mass reinforced using three reinforcement layers, one of which was actively tensioned while the two neighboring layers remained passive. The neighboring reinforcement layers received stresses from the tensioned reinforcement through the shear stresses transferred to the intermediate soil medium. In this study, a number of soil–reinforcement interaction tests were conducted with different reinforcement and soil types. Test results indicate that the load conveyed to the neighboring reinforcement increased with increasing tension in the loaded reinforcement layer. The magnitude of load transfer was found to increase with increasing soil–reinforcement interaction. At least for the products used in this study, geogrid reinforcements showed a greater ability to form a composite reinforced soil mass than geotextile reinforcements.

The low viscosity and the ability to control solidification rate make colloidal nanosilica grout an excellent ground-improvement solution which is functional for different engineering purposes. A comprehensive experimental programme was performed to test the effectiveness and applicability of low-pressure injection of aqueous nanosilica suspensions against seismic liquefaction and to provide the experimental basis for the design, execution, and control of treatments. Scanning electron microscope and X-ray diffraction tests carried out on samples prepared with variable dosages enabled analysis of the microstructure of the original material and grouted sand. The influence of the grout composition on the solidification rate, viscosity, and shear strength of the treated sand was evaluated with preliminary tests to optimize the use of material. The efficacy of treatment in terms of stress–strain response and liquefaction resistance was investigated with a series of drained monotonic and undrained cyclic triaxial tests. A quality control procedure based on sonic wave transmission was established by performing bender element tests on samples cured for different times. The intent was to find the trade-off between a cost-effective use of materials and the mechanical performance of the treated sand.

Dynamic centrifuge tests were performed to investigate multidirectional loading effects on the shear and volumetric response of saturated sands under partially drained, level-ground conditions. These tests illustrate that dense sand shear response is not affected significantly by multidirectional shaking and can be estimated reasonably by one-dimensional nonlinear total and effective stress site response analyses. Multidirectionality factors for both excess porewater pressure ($\mathrm{MDF}{r}_u$) and vertical strain ($\mathrm{MDF}{\epsilon }_v$) tended to increase with density and decrease with shaking intensity. Specifically, $\mathrm{MDF}{r}_u$ ranged from about 1 to 4, with an average value of about 2 for low $r_u$ values and $\mathrm{MDF}{r}_u$ approaching unity as the soil approaches liquefaction. Similarly, $\mathrm{MDF}{\epsilon }_v$ ranged from about 1 to 3, with an average value of about 2 for low $r_u$ values and $\mathrm{MDF}{\epsilon }_v$ approaching 1.3 as the soil approached liquefaction. Multidirectionality factors as functions of the factor of safety against liquefaction are proposed that differ from constant MDFs recommended elsewhere. Lastly, energy-based intensity measures provided nearly unique estimates of excess porewater pressure and vertical strain for both uni- and bidirectional motions, avoiding the need for MDFs.

A set of dynamic centrifuge experiments was performed to assess the effect of the depth of the groundwater table on the seismic site response and kinematic interaction of a foundation on unsaturated sandy soil. The experimental program consisted of centrifuge tests on dry soils, saturated soils, and soils having groundwater level at various depths. Results show that as the groundwater level was lowered, (1) seismically induced soil settlement, the mean period of the free-field motion, and the midperiod amplification factor generally decreased; (2) the lateral incoherence parameter, soil strain–dependent natural frequency, and amplification factors for peak ground acceleration, Arias Intensity, and short period roughly increased; while (3) the rocking incoherence parameter stayed approximately constant. Assuming soils in a fully saturated state for seismic design may either over- or underpredict different aspects of the seismic soil–foundation response, in comparison with partially unsaturated ground. Thus, this assumption may not always lead to safe or economical designs, especially with regard to seismically induced soil settlement, seismic site response analysis, and kinematic soil–foundation interaction.

Performance-based probabilistic approaches (PBPAs) for estimating seismically-induced slope displacements ($D$) provide hazard-consistent estimates through the evaluation of $D$ hazard curves (DHCs), and hence, its use in practice is appealing. Importantly, the epistemic uncertainty to develop a DHC needs to be considered, which is typically done using a logic tree approach with discrete branches for the system properties and seismic displacement models (SDM). However, the few existing SDMs, do not allow one to accurately capture the full epistemic uncertainty range. This study uses the polynomial chaos (PC) theory to develop a computationally efficient framework for propagating the epistemic uncertainty in the median $D$, associated with alternative SDM models. PC expansions allow one to account for the epistemic uncertainty distribution in DHCs in a computationally efficient manner, which cannot be possible using the traditional logic tree approach. The necessary steps for the implementation of the proposed framework are discussed, and an illustrative example of its application in engineering practice is presented.

Model tests and field measurements were carried out to study the mechanical behavior of cobble-rich soil in response to shield tunneling. In particular, an experimental investigation was carried out using a laboratory-scale model. The model used includes a miniature shield machine that can approximate real tunnel construction, replicating the in-situ methods of excavation and support. The surface settlement and subsurface deformation were analyzed, and these data were compared with predictions based on previous studies. The results confirm that the model tests can effectively simulate the principal operations of a real earth-pressure-balance machine. The observed surface settlement troughs in both the transverse and longitudinal directions were found to be narrower than in clay or sandy soils. With respect to subsurface deformation, the deformation zone width decreases almost linearly as a function of depth.

This paper presents an experimental investigation on the effects of strain history and aging on cyclic response and resistance of fine-grained coal refuse (FCR) using large-scale shaking table tests. The FCR specimen was slurry-deposited in a membrane-lined laminar shear box and subjected to three shaking events on a 1-g shaking table. Sensors were used to measure the FCR’s dynamic response during shaking, and a piezocone penetrometer (CPTu) was used to measure soil resistance and estimate the cyclic behavior of the FCR specimen before and after each shaking test for time intervals up to 97 days. Based on the CPTu tests, the freshly deposited FCR specimen was classified as sensitive fine-grained soil after deposition and self-consolidation. An irregular pore pressure pattern was measured during and after the shakes due to heterogeneity of the FCR specimen. The FCR specimen experienced cyclic mobility and pore pressure redistribution, indicating that the material may be vulnerable to large deformations after cyclic loading. Cone tip resistance immediately after the first shaking event showed limited strength loss due to the original loose structure of the FCR. Each shaking event progressively densified the FCR specimen and increased the cyclic resistance. However, the FCR specimen remained susceptible to cyclic softening and flow liquefaction. The FCR specimen was classified using the CPTu data as clayey silt to silty clay after two shakes and 97 days of aging. Cone tip resistance increased over 100% by 97 days after the second shaking event with a rate of strength increase slower than the rate observed for clean sand in an earlier study. The increase in CPT tip resistance over time was quantified, and an equation to estimate the undrained shear strength of FCR as a function of normalized tip resistance and time after a shaking event was developed and calibrated.

On May 25, 2016, an artificial riverbank of the Arno River collapsed just upstream from the famous Ponte Vecchio bridge in the city of Florence, Italy, a UNESCO World Heritage Site. An analysis of the failure was performed to identify the damage condition of the involved structures, to define the causes of the failure, and preserve the site. This study was based on borehole integration and geotechnical characterization, terrestrial laser scanner (TLS) and digital photogrammetry (DP), bathymetric and geophysical surveys, riverbank stability analysis, and wall seismic vibrations assessment. The TLS survey results were used to characterize the three-dimensional (3D) wall deformations pattern, the landslide geometry, and to define the involved volumes. The riverbank stability analysis demonstrates that the lower safety factor was obtained in the case of complete saturation of filling materials and low river level in accordance with the major cause of collapse being attributed to the loss of water from subterranean pipes.

Consolidation parameters are required to support the disposal management of soft soils or mine tailings. The estimation of these parameters from simple correlations using easily measured properties can be advantageous, and considerable work has been done on this topic. This paper proposes two innovations that advance this work: (1) hydraulic conductivity–void ratio ($k\text{-}e$) estimation can be substantially improved by using a single measured value at a high-void ratio, and (2) the compressibility curve itself can be a useful predictor of $k\text{-}e$. Using these findings, general equations are derived that describe $k\text{-}e$ using a power law, where the power is either 4 or 5. Examining 79 $k\text{-}e$ data sets from clays, clayey tailings, and dredged materials, 94% of all predicted $k$ values are within an order of magnitude of measured $k\text{-}e$ values. This level of accuracy, coupled with the advantage of anchoring the $k\text{-}e$ function by a measured value at a high-void ratio, is shown to result in robust predictions of settlement in large strain consolidation analyses.

This paper evaluates the current state of practice to determine the average shear wave velocity of improved ground sites and proposes an alternative method that adequately captures the reinforcement effects of ground improvement elements. To estimate the actual stiffness of improved grounds and to develop benchmark data, continuum finite-element models of improved grounds with various area replacement and stiffness ratios are analyzed. The study shows that the common approach, i.e., the area replacement ratio weighted average shear wave velocity, significantly overestimates the improved ground average velocity. This may lead to an incorrect determination of a code-based site class, spectral accelerations, and seismic structural loads. The proposed alternative approach is shown to be capable of providing a reasonable estimate of the actual stiffness of improved grounds.

This paper presents a field test on the axial and radial thermal responses of friction-type energy piles embedded in clay under monotonic thermal loads (2.5 and $5.0\mathrm{kW}$). The inlet and outlet water temperature, pile temperature, and strain were monitored. The heat exchange efficiency and thermal response of the energy pile are discussed and analyzed. Further comparative analyses of friction-type energy piles embedded in compacted sand showed that the radial thermal stress of a pile is much lower than the axial thermal stress, which may not play a major role in soil–structure interaction. The axial thermal stress of an energy pile embedded in clay increases with increasing axial constraint. The constraint of the energy pile cannot be simply predicted through the shear strength of the sand. The influence of the radial thermal stress produced during the operation of the energy piles on the bearing capacity of the pile can be disregarded, especially in soft soil.