Journal of Geotechnical and Geoenvironmental Engineering

In cities, seismic coupling between structures is known to influence ground motions, settlement patterns, and demand on superstructures. Yet the effects of interactions between soil and building clusters on structural performance are poorly understood, particularly on ground susceptible to liquefaction. Existing analytical methods cannot capture the nonlinearity and complexity of seismic interactions between adjacent buildings and softened soil, while advanced numerical tools that can capture such complexities have not been validated. Consequently, liquefaction mitigation measures designed assuming no interaction between structures may perform poorly. To evaluate the appropriateness and effectiveness of a common mitigation strategy—prefabricated vertical drains—in urban environments, a series of experiments were conducted on a geotechnical centrifuge. Closely spaced, dissimilar, realistic model structures were placed on a layered liquefiable soil deposit and subjected to realistic earthquake motions. Mechanistic consequences of seismic coupling due to the use of drains around the shorter structure were evaluated. The results show that the use of drains around one structure may have drastic consequences for the performance of an adjacent unmitigated structure, even causing its collapse. Engineers and planners must consider integrated mitigation strategies in dense urban environments with the goal of improving performance in building clusters rather than individual buildings.

Prefabricated vertical drains (PVDs) are commonly used to mitigate the liquefaction hazard and its consequences. However, the influence of enhanced drainage on the response and performance of soil, foundation, and structure is not well understood, hindering the development of performance-based mitigation design procedures. This paper presents results of three centrifuge experiments on 3-story and 9-story, potentially inelastic, moment-resisting structures founded on a layered liquefiable soil deposit. The paper explores the influence of PVDs on pore pressures, foundation settlement and tilt, accelerations on the foundation and structure, and deformation patterns within the beam and column fuses. Test results indicate that PVDs can be successful in reducing the extent and duration of large excess pore pressures and net foundation settlements. However, they are also generally associated with an increase in transverse acceleration and deformation demands on the foundation and superstructure. The influence of PVDs on these seismic demands and on a foundation’s permanent tilt depends strongly on the structure’s strength and dynamic properties as well as ground motion characteristics. In the case of taller, heavier, and weaker structures, this increased demand can amplify $\mathrm{P}\text{-}\mathit{\Delta }$ effects, particularly when the motion resonates with building’s modal frequencies, amplifying the foundation’s permanent rotation and the structure’s flexural deflections with potentially severe consequences. These results point to the importance of considering the performance of the entire soil–foundation–structure system in an integrated manner in mitigation design.

The probabilistic analysis of geotechnical structures presenting spatial variability in the soil properties is generally performed using Monte Carlo simulation (MCS) methodology. Despite being robust and accurate, MCS has low efficiency when considering the small failure probabilities encountered in practice. This is because it is very time-expensive in such cases due to the large number of simulations required to calculate a small failure probability with a small value of the coefficient of variation of this failure probability. In order to reduce the number of calls of the mechanical model when performing a probabilistic analysis, this paper uses the active learning reliability method combining kriging and Monte Carlo simulation (AK-MCS). This method is shown to be very efficient because the obtained probability of failure is very accurate, needing only a small number of calls to the computationally expensive mechanical model compared with MCS methodology. This study involves a probabilistic analysis at the ultimate limit state of a strip footing resting on a spatially varying soil using the AK-MCS approach. The soil cohesion and angle of internal friction are considered as random fields. The mechanical model is based on numerical simulations using the finite-difference code ${\mathrm{FLAC}}^{3\mathrm{D}}$. The obtained probabilistic numerical results are presented and discussed.

The axial and radial thermal responses of a field-scale energy pile installed in dense sand and subjected to monotonic and cyclic temperatures are examined. It is found that the axial thermal strains in the pile are more restricted to thermal expansion/contraction compared to radial thermal strains. The radial thermal strains are close to that of a pile expanding/contracting freely, indicating minimal resistance from the surrounding soil in the radial direction. As a result, very low magnitudes of radial thermal stresses developed in the pile compared to axial thermal stresses. The pile–soil radial contact stresses estimated from the cavity expansion analysis are up to 12 kPa for a pile temperature change of 22.5°C and are likely to stay low for the range of commonly encountered operating temperatures for cast-in-place concrete energy piles installed in dense sand. During cyclic heating and cooling, unstable changes in axial and radial thermal strains were observed initially during initial cycles, indicating a ratcheting response. The changes in strains became more stable over further cycles without significant changes in side friction or pile–soil contact stresses.

Results of a centrifuge experiment simulating seismic site response in a layered level liquefiable soil profile are used to evaluate and systematically compare the predictive capabilities of two common numerical platforms and two classes of advanced soil constitutive models (multiyield and bounding surface) used by three different teams. The pressure-dependent multiyield (PDMY02) and simple anisotropic SAND (SANISAND) constitutive models, implemented in open source and commercially available software, were independently calibrated by three teams using the same set of monotonic and cyclic triaxial test results. Class C predictions of the elastoplastic soil response in centrifuge following verification and initial calibration showed excessive dilative tendencies in all constitutive models to different degrees. These tendencies led to a notable overestimation of acceleration spikes at higher frequencies and an underestimation of net excess pore pressures in dense sand. The second calibration phase focused primarily on reducing soil’s dilative tendencies to match centrifuge tests, even at the cost of slightly sacrificing aspects of the response at an element level or abandoning the number of cycles to liquefaction. Despite differences in calibration methodologies and priorities among three modelers, the results show that small element tests and centrifuge experiments do not always lead to the same calibrated soil parameters. Further, although current numerical platforms and advanced constitutive models were capable of reproducing many aspects of seismic site response observed in the centrifuge, they still need fundamental improvements to capture volumetric settlements. This is an old problem that needs attention in future numerical and physical model studies.

Sampling and laboratory testing of soils is often necessary to evaluate site-specific soil properties. Prior research has been primarily performed for clays, producing accepted practices that enable reliable soil characterization via laboratory testing [e.g., $\mathrm{\Delta }e/e_0$ and sample quality designation (SQD)]. Synthetic mixtures of nonplastic to plastic silts and clays are tested using oedemetric constant rate of strain consolidation. Results indicate trends of increasing sample quality with decreasing plasticity and in situ overburden stress that are independent of the level of induced disturbance. A framework for assessing sample quality based on concepts of work and strain-energy is developed and shown to be independent of these effects. Normalization of the initial recompression slope ($C_r$ or $C_{rw}$) by the virgin compression slope ($C_c$ or $C_{cw}$) results in an index $C_r/C_c$ (or $C_{rw}/C_{cw}$) that accurately captures disturbance for soils across a wide range of tested conditions. This method is further evaluated using data from published prior studies.

This paper presents an investigation of coupled thermal, hydraulic, and chemical behavior of a compacted bentonite buffer under the heating and hydration conditions of geological disposal of high-level nuclear waste. The study presented provides further insight into the evolution of hydro-geochemistry of the compacted bentonite and the clay microstructure effects through a numerical modelling development of the reactive transport of multicomponent chemicals. The application/validation case study is based on a series of laboratory tests on heating and hydration of compacted bentonite for a period of 0.5–7.6 years reported in the literature. The effects of microstructure evolution during hydration and dehydration on the transport phenomena are included via a new approach that links the geochemistry of clay hydration/dehydration with the transport properties. The analysis results related to the moisture flow and chloride transport demonstrate close correlation with the experimental results by the inclusion of the effects of microstructure evolution in the transport phenomena. The results of numerical analysis of reactive transport of chemicals highlight the importance of accessory minerals present in bentonite on the distribution of some anionic species. The behavior of major cationic species is shown to be mainly governed by the transport processes. Further insights into the chemically driven processes in clay buffer due to coupled hydraulic and thermal effects are presented and discussed that are captured from the results of modeling the clay-water-chemical system.

Geosynthetic clay liners (GCLs) are increasingly used in engineering and environmental applications that include nonstandard solution chemistry. Long-term exposure of geosynthetics to nonstandard solutions in containment facilities, such as heap leach pads, municipal and hazardous solid waste containment, and so on, may cause degradation of bentonite and polymeric components and alter the hydraulic and mechanical properties of GCLs. Leachate collected from full-scale containment facilities has commonly been used in previous studies for field-focused GCL-related experiments. However, due to problems associated with using actual leachates, representative synthetic solutions often are used. A step-by-step procedure for the design, preparation, and verification of representative synthetic mining solutions for laboratory testing on GCLs is described in this study. Recipes for creating three synthetic mining solutions to simulate gold, copper, and bauxite process solutions are presented. The procedure for solution development and prepared solutions were verified via comparison of measured to calculated metals concentrations, which yield concentration differences less than 8% for all three synthetic process solutions.