The presence of underground structures within fault zones has the potential to alter deformation patterns on the ground surface, thereby placing existing structures-typically regarded as safe-at risk. This paper presents findings from four centrifuge model tests and 3D numerical simulations exploring the effects of tunneling in fault zones. This study investigated the values associated with foundation rotation, surface deformations, and the patterns of fault rupture propagation through various soil strata. The results demonstrate that the presence of a tunnel alters the interaction pattern between fault rupture and foundation systems, which can lead to an increase in foundation rotation. Notably, the findings indicate that a precise consideration of superstructure shape can enhance foundation rotation by up to 23%. Furthermore, the presence of a tunnel in the fault zone causes substructures to endure major damage from vertical fault displacements exceeding 0.6 m. In contrast, these substructures experienced similar levels of damage at vertical fault displacements of 1.7 m in the absence of tunnels.

Physical modeling is an efficient method to simulate practical geotechnical problems and to provide insights into soil behavior. This study used geotechnical centrifuge models equipped with motorized pulling systems to pull coupons (thin metal plates) at constant speeds horizontally through clean, saturated sand models that were liquefied by cyclic loading. The model setup was aimed to mimic shearing mechanisms, large shear strains, and large strain rates observed in field-scale flow slides. In-flight cone penetration testing and bender element-based shear wave velocity measurements helped in characterizing soil state at coupon levels before liquefaction. In addition, a miniature pressure transducer was embedded in the coupon along its top horizontal surface to directly measure pore pressure response on the shear surface within the liquefied soil. In total, 11 coupon pulls were completed, with 6 of the 11 tests providing shear-induced pore pressure measurements at the coupon surface. Measured coupon pulling forces and pore pressure responses at shear-surface and free-field were interpreted to identify key behaviors. These key behaviors illustrated that relatively low coupon velocities were required to maintain liquefied conditions at the coupon surface. In addition, pulling force recovery during pore pressure dissipation appeared to be related to coupon velocity (i.e. strain rate).

Centrifuge-based physical modeling is widely adopted for understanding the performance of geostructures, like reinforced slopes, clay liners of municipal solid waste landfills, geogrid-reinforced soil walls, earthen dams, soil nailed slopes, etc. This study aims to highlight the benefits of centrifuge-based physical modeling in order to comprehend the performance of different geostructures both prior to and during failure. Firstly, a discussion is made on scaling considerations along with modeling aspects of various types of phenomena like rainfall, flooding, etc. Further, details of four types of balanced/beam centrifuge equipment used for understanding the behavior of various types of geostructures at high gravity conditions, along with errors due to radial acceleration field, are also presented. In the process, innovative development of cost-effective actuators for simulating: (1) continuous differential settlements of landfill lining systems, (2) seepage of water through a slope, (3) seepage-induced flooding, (4) dynamic compaction, (5) rainfall-induced seepage, and (6) pseudo-static seismic loading along with flooding-induced seepage has been done. Different types of instrumentation units like potentiometers (P), linearly variable differential transformers, pore-water pressure transducers, load cells, accelerometers, strain gauges, etc., along with wireless data acquisition systems were used for monitoring the performance of the models during centrifuge tests. Additionally, the use of particle image velocimetry, digital image analysis, and the digital-cross correlation technique to evaluate the performance of several models evaluated at high gravity is covered. Lastly, it has been sufficiently shown that using digital image analysis/digital image correlation approaches in conjunction with centrifuge-based physical modeling analysis is a useful study tool. Insights gained in understanding the behavior of geostructures in a geotechnical centrifuge, especially subjected to climatic events like rainfall, flooding, and earthquakes, are highly significant and help in designing and constructing geostructures with confidence to engineers.

A series of dynamic centrifuge modeling tests were conducted to evaluate the volumetric threshold shear strain of loose gravel-sand mixtures composed of various ratios of gravel and sand by weight. The maximum and minimum void ratios of the mixtures were evaluated, and the optimum packing condition was determined when the mixture contained approximately 60-70 % gravel by weight. A total of six centrifuge modeling tests were performed at 50-g centrifuge gravitational acceleration. Each centrifuge model was subjected to six shaking events consisting of uniform sinusoidal motions with various amplitudes and numbers of cycles. During the entire duration of the test, the development of excess pore water pressure and settlement was monitored. Empirical relationships of pore water pressure ratio and shear strains were developed for these mixtures. The development of excess pore water pressure in the mixtures with greater than 60 % gravel exhibits transient behavior, while residual excess pore water pressure was observed in the mixtures with less than 60 % gravel. Based on the results, the volumetric threshold strain evaluated from the generation of pore water pressure and volume change during shaking is similar. The values were found to be in a range of 0.03-0.10 % and are influenced by soil composition. The threshold strain increases as the amount of gravel in the soil mixture increases.

The batter piles of a pile-supported wharf are severely damaged under excessive lateral loads, and effective reinforcement strategies are of great concern. In this paper, the effect of different reinforcement strategies on the lateral bearing performance of the wharf, taking into account the pile-soil interaction, was investigated using centrifuge test and numerical simulation. The results showed that both reinforcement strategies were effective in improving performance, with results generally aligning with those of the intact wharf in terms of load-displacement relationships, and significantly reduced the magnitudes of pile lateral deflection, soil pressure, bending moment, and shear force compared to the broken wharf. However, the concrete jacketing method resulted in larger lateral deflections in the middle sections of the retrofitted batter piles, and then abruptly reduced to match those of the steel-bonding method in the cap-pile regions. The degree of abrupt changes of bending moment in retrofitted batter piles was more distinct in the concrete jacketing wharf than that in the steel-bonding wharf. The steel-bonding method distributed the lateral load more evenly than the concrete jacketing, which involved more abrupt changes in shear forces. Overall, although the performance of both retrofitting methods was slightly better than that of the intact wharf at component level, the steel-bonding method appeared to prove superior due to the smaller change in stiffness and the more even distribution of lateral loads.

This study focuses on predicting the impacts of a heating-cooling cycle on the pullout capacity of energy piles installed through a soft clay layer. Geotechnical centrifuge physical modeling was used to evaluate temperature, pore water pressure, volume change, and undrained shear strength profiles in clay layers surrounding energy piles heated to different maximum temperatures to understand their impacts on the pile pullout capacity. During centrifugation at 50 g, piles were jacked-in at a constant rate of penetration into a kaolinite clay layer consolidated from a slurry in a cylindrical aluminum container, heated to a target temperature after stabilization of installation effects, cooled after completion of thermal consolidation requiring up to 30 hours (1250 days in prototype scale), then pulled out at a constant rate. T-bar penetration tests were performed after the heatingcooling cycle to assess differences in clay undrained shear strength from a baseline test. The pullout capacity of an energy pile heated to 80 degrees C then cooled to ambient temperature was 109 % greater than the capacity in the baseline test at 23 degrees C, representing a substantial improvement. The average undrained shear strength measured with the T-bar at a distance of 3.5 pile diameters from the pile heated to 80 degrees C was 60 % greater than at 23 degrees C but followed the same trend as pile capacity with temperature. An empirical model for the pullout capacity was developed by combining predictions of soil temperature, thermal excess pore water pressure, thermal volumetric strain, and undrained shear strength for different maximum pile temperatures. The empirical model predictions matched well with measured pullout capacities.

Most natural granular deposits are spatially variable due to heterogeneities in soil hydraulic conductivity, layer thickness, relative density, and continuity. However, existing simplified liquefaction evaluation procedures treat each susceptible layer as homogeneous and in isolation, neglecting water flow patterns and displacement mechanisms that result from interactions among soil layers, the groundwater table, foundation, and structure. In this paper, three-dimensional, fully coupled, nonlinear, dynamic finite-element analyses, validated with centrifuge experimental results, are used to evaluate the influence of stratigraphic layering, depth to the groundwater table, and foundation-structure properties on system performance. The ejecta potential index (EPI) serves as a proxy for surface ejecta severity within each soil profile. The results reveal that among all the engineering demand parameters (EDPs) and geotechnical liquefaction indices considered, only EPI predicted a substantial change in the surface manifestation of liquefaction due to changes in the location of the groundwater table and soil stratigraphy. This trend better follows the patterns from case history observations, indicating the value of EPI. Profiles with multiple critical liquefiable layers at greater depths resulted in base isolation and reduced permanent foundation settlement. Ground motion characteristics have the highest influence on EDPs, among the properties considered. The outcropping rock motion intensity measures with the best combination of efficiency, sufficiency, and predictability were identified as cumulative absolute velocity (for predicting foundation's permanent settlement and free-field EPI) and peak ground velocity (for peak excess porepressure ratio). These results underscore the importance of careful field characterization of stratigraphic layering in relation to the foundation and structural properties to evaluate the potential liquefaction deformation and damage mechanisms. The results also indicate that incorporating EPI alongside traditional EDPs shows promise.

The monopile response to lateral load under different liquefaction phases via centrifuge modeling tests is reported in this paper. The test was performed in viscous scaling mode to match the loading time and flight speed at a centrifuge acceleration of 80 g. A mixture of methylcellulose powder in water increased the viscosity by 80 times compared with water at a concentration of 0.47%. The seismic input is applied with a frequency of 1 Hz to achieve soil liquefaction. During the test, the monopile received the lateral load. The liquefaction regime was divided into four distinct phases based on the excess pore water pressure ratio during loading: total liquefaction, two tests during the period of degradation of pore pressure when the excess pore water pressure ratio was 0.67 and 0.32, and the last test at the end of liquefaction. The results reveal that pore water pressure distribution slightly differs in the free field and surrounding pile. The shallow layer started to liquefy early in response to the ground acceleration. The entire monopile body rotated owing to 0.48 m of pile head displacement during full liquefaction when the lateral load applied reached 290 kN. During the liquefaction regime, the profile of the pile behaviors migrating from a slender pile to a rigid pile is a significant discovery in this study. A large shear force appeared one-third of the pressure to the bottom of the monopile, and the maximum bending moment location became deeper, with a value of 65% greater than at the end of liquefaction.

Stiff in-ground structural or diaphragm walls have previously been used as a liquefaction countermeasure for existing building structures. The available design methodologies for typical mitigation techniques are based on free-field conditions, disregarding seismic interactions among soil layers, mitigation, foundation, and superstructure. In this paper, we use three-dimensional (3D) fully-coupled nonlinear finite-element analyses, validated with centrifuge test results, to evaluate how the properties of structural walls (SWs) in layered liquefiable soils affect the seismic performance of a potentially inelastic structure on mat foundations. The SWs were shown to reduce foundation's permanent settlement in most cases (although not to acceptable levels), at the expense of its peak transient and residual tilt. However, SWs amplified the foundation's settlement in cases involving a thick, dense draining crust (Hcrust >= 4m) or a uniform and thick medium to dense sand layer. Increasing the wall's penetration into the lower dense sand layer and its flexural stiffness were shown to be effective in reducing foundation settlement by reducing shear-type deformations within the critical layer. Simultaneously, increasing the foundation-to-SW distance amplified settlement by increasing the potential for accumulation of shear strains. For the cases considered, foundation tilt was relatively insensitive to changes in wall geometry and flexural stiffness. Overall, Hcrust was the most influential parameter for mitigation effectiveness in terms of permanent settlement and tilt, followed by the relative density of the critical layer. The limited numerical sensitivity study presented in this paper shows that SWs may not always benefit the overall performance of the soil-foundation-structure system, and their design requires consideration of system and ground motion characteristics with great care.

Seismic loading has been widely recognized as a critical factor contributing to soil liquefaction. This paper introduces centrifuge tests conducted to characterize the seismic response of clayey sand foundations under surcharge induced by upper structures such as dams, with a focus on examining the effectiveness of different liquefaction mitigation measures. Three models with a surcharged block above are considered: one with soil untreated, one improved with stone columns, and the other enhanced by closed diaphragm walls. In addition, a free ground model is tested to examine the dynamic characteristics of the tested soil. Results show that the soil used is prone to liquefaction, but this trend can be somewhat suppressed by the presence of the surcharge. However, the excess pore pressure within the shallow layer keeps rising after shaking, posing the surcharged structure to instability. With the inclusion of stone columns, seepage can be effectively facilitated, thus eliminate the large pore pressure concentration. The construction of closed diaphragm walls effectively reduces the surface settlement by providing lateral restraint of the soil core. This investigation sheds light on the liquefaction mitigation mechanisms of different measures for clayey sand subjected to large overburden and provides references for improving the seismic design.