Hydraulic conductivity plays a significant role in the evolution of liquefaction phenomena induced by seismic loading, influencing the pore water pressure buildup and dissipation, as well as the associated settlement during and after liquefaction. Experimental evidence indicates that hydraulic conductivity varies significantly during and after seismic excitation. However, most previous studies have focused on experimentally capturing soil hydraulic conductivity variations during the post-shaking phase, primarily based on the results at the stage of excess pore water pressure dissipation and consolidation of sand particles after liquefaction. This paper aims to quantify the variation of hydraulic conductivity during liquefaction, covering both the co-seismic and postshaking phases. Adopting a fully coupled solid-fluid formulation (u-p), a new back-analysis methodology is introduced which allows the direct estimation of the hydraulic conductivity of a soil deposit during liquefaction based on centrifuge data or field measurements. Data from eight well-documented free-field dynamic centrifuge tests are then analysed, revealing key characteristics of the variation of hydraulic conductivity during liquefaction. The results show that hydraulic conductivity increases rapidly at the onset of seismic shaking but gradually decreases despite high pore pressures persisting. The depicted trends are explained using the KozenyCarman equation, which highlights the combined effects of seismic shaking-induced agitation, liquefaction, and solidification on soil hydraulic conductivity during the co-seismic and post-shaking phases.

Large-diameter monopiles of offshore wind turbines are subjected to continuous multistage cyclic loads of different types (one-way or two-way) and loading amplitudes over time. The loading history is likely to affect the lateral response during the subsequent loading stage. This paper conducts a systematic study on the lateral response of monopiles with and without reinforcement in multilayer soil. Two groups of monotonic centrifuge tests of monopiles with and without reinforcement are carried out to compare and study the influence of reinforcement on the displacement, bending moment and earth pressure of monopile foundations. Local reinforcement in the shallow layer effectively improved the bearing capacity of the monopile foundation. The ultimate bearing capacity of monopile foundations in monotonic tests provides a load basis for cyclic tests. Four groups of continuous multistage cyclic centrifuge tests of monopiles with and without reinforcement with different cyclic modes and loading amplitudesare carried out to investigate the influence of loading history on the lateral cumulative displacement, unloading secant stiffness and bending moment. Empirical design recommendations for monopiles under continuous multistage cyclic loads with different cyclic modes and loading amplitudes are provided based on the results of the tests.

This article introduces a novel system identification technique for determining the bulk modulus of cohesionless soils in the post-liquefaction dissipation stage following seismic excitation. The proposed method employs a discretization of Biot's theory for porous media using the finite difference method. The technique was validated using synthetic data from finite elements simulations of an excited soil deposit. These numerical simulations were performed using an advanced multi-yield surface elastoplastic model. Additionally, the technique was used to analyze a series of high-quality dynamic centrifuge tests performed on Ottawa F-65 sand as part of the LEAP- 2020 project. A comparative analysis between recorded and identified bulk modulus values highlights the effectiveness of the proposed technique across a wide range of conditions.

The dynamic response of piles is a fundamental issue that significantly affects the performance of pile foundations under vertical cyclic loading, yet it has been insufficiently explored due to the limitations of experimental methods. To address this gap, a hydraulic loading device was developed for centrifuge tests, capable of applying loads up to 2.5 kN and 360 Hz. This device could simulate the primary loading conditions encountered in engineering applications, such as those in transportation and power machinery, even after the amplification of the dynamic frequency for centrifuge tests. Furthermore, a design approach for model piles that considers stress wave propagation in pile body and pile-soil dynamic interaction was proposed. Based on the device and approach, centrifuge comparison tests were conducted at 20 g and 30 g, which correspond to the same prototype. The preliminary results confirmed static similarity with only a 1.25% deviation in ultimate bearing capacities at the prototype scale. Cyclic loading tests, conducted under various loading conditions that were identical at the prototype scale, indicated that dynamic displacement, cumulative settlement, and axial forces at different burial depths adhered the dynamic similarity of centrifuge tests. These visible phenomena effectively indicate the rationality of centrifuge tests in studying pile-soil interaction and provide a benchmark for using centrifuge tests to investigate soil-structure dynamic interactions.

Revetment breakwaters on reclaimed coral sand have demonstrated vulnerability to seismic damage during strong earthquakes, wherein soil liquefaction has been identified as a substantial contributor. Based on the results of three centrifuge shaking table tests, this study investigates the characteristic seismic response of revetment breakwater on reclaimed coral sand and the influence of soil liquefaction. The basic mechanical properties of reclaimed coral sand were measured using undrained triaxial and hollow cylinder torsional shear tests. The centrifuge test results indicate that liquefaction of coral sand can result in significant displacement and even failure of revetment breakwaters, encompassing: (a) tilting, horizontal displacement, and settlement of the crest wall; (b) seismic subsidence in the foundation and backfill. The liquefaction consequence of the reclaimed coral sand increased with a decrease in soil density and rise in sea water level (SWL). Post-earthquake rapid reinforcement measure via sandbags is found to be effective in limiting excess pore pressure buildup in foundation soil and structure deformation under a second shaking event. Based on the test results, the effectiveness of current simplified design procedures in evaluating the stability and deformation of breakwaters in coral sand is assessed. When substantial excess pore pressure generation and liquefaction occur within the backfill and foundation coral sand, the pseudo-static and simplified dynamic methods are inadequate in assessing the stability and deformation of the breakwater.

The primary goal of this study is to provide an efficient numerical tool to analyze the seismic performance of nailed walls. Modeling such excavation supports involves complexities due partly to the interaction of support with soil and partly because of the amplification of seismic waves through an excavation wall. Consequently, innovative modeling is suggested herein, incorporating the calibration of the soil constitutive model in a targeted range of stress and strain, and the detection of a natural period of complex systems, including soil and structure, while benefiting from Rayleigh damping to filter unwanted noises. The numerical model was achieved by simulating a previous centrifuge test of the excavation wall, manifested at the pre-failure state. Notably, the calibration of the soil constitutive model through empirical relations, which replaces the numerical reproduction of an element test, more accurately simulated the soil-nail-wall interaction. Two factors were crucial to a successful result. First, probing the natural period of the complicated geometry of the model by applying white noises. Second, considering Rayleigh damping to withdraw unwanted noises and thus assess their permanent effects on the model. Rayleigh damping was applied instead of filtering the obtained results.

The demand for tunnels in densely populated urban areas is growing rapidly to address mobility challenges. Mechanized tunneling is widely adopted in urban environments due to its high productivity and the relatively small ground deformations it induces. However, urban tunneling is highly complex because of the typically shallow depths and interactions with aboveground structures. Therefore, accurately predicting ground deformations induced by mechanized tunneling at the design stage is crucial for assessing potential building damage. To investigate these deformations, a series of centrifuge tunnel tests have been conducted at academic institutions such as the Universities of Cambridge and Nottingham to study the behavior of shallow mechanized tunnels in cohesionless soil. These tests serve as excellent benchmarks for numerical model calibration. Once calibrated to replicate centrifuge test results, numerical models can efficiently analyze a wide range of scenarios at a fraction of the time and cost. This paper investigates ground deformations induced by shallow tunneling in cohesionless soil using numerical models calibrated against selected centrifuge tunnel tests, which encompass varying tunnel diameters, depths, and sand relative densities. The numerical modeling results presented in this paper provide extensive insights into tunnel behavior, illustrating how tunnels respond to different relative densities and depths under tunnel volume losses of up to 5%, approaching failure conditions. Additionally, a comprehensive analysis of ground deformations caused by shallow tunnels in sandy soils and their potential impact on buildings is presented.

The significant reduction in the stiffness of liquefied soil is accompanied by a decrease in the shear wave velocity, which ultimately results in the softening of the liquefied site. Time-frequency response analysis can identify the sudden drop in the frequency of the liquefied site, which has been widely employed to determine the onset of liquefaction. However, using the modal frequency (corresponding to the maximum power at each time step) to identify the timing of liquefaction (tL) captures the reduction in frequency during earthquakes, but it does not encompass the entire range of frequencies that have changed. Furthermore, previous literature defines tL as the boundary separating the modal frequency into pre- and postliquefaction time segments, but this estimate does not consider the generation of pore water pressure. Two representative case histories are presented to highlight the limitations of identifying tL by solely relying on the modal frequency approach that uses a two-step function. As a result, this study introduces an innovative method to identify tL utilizing the spectral energy ratio (SER), which captures the entire frequency shift. A step-by-step procedure using SER is detailed, and the new estimates of tL are compared with those derived from previous literature using 30 case histories. To validate the approach, a sensitivity analysis was performed using centrifuge test data from the Liquefaction Experiment and Analysis Projects. Results indicated that incorporating a ramp that accounts for pore water pressure buildup in the trilinear function improved tL estimation. An optimized SER value of 0.92 was determined for the proposed method. The notable contribution of this study is an enhanced approach of identifying the timing of liquefaction triggering by only utilizing acceleration records without requiring pore water pressure responses.

Centrifuge tests were performed to study the dynamic properties of shallow soil with locally raised bedrock (i.e. variable soil depth). The test parameter was the slope of bedrock: 0 degrees (S0), 35 degrees (S35), and 45 degrees (S45). In each test, accelerations were measured along the soil depth, and the results of acceleration, displacement, Fourier transform, and response spectrum were compared. Based on the results, the transfer function (TF), the ratio of response spectrum (RRS), and the site period were estimated. The ground motion and site period of specimens with raised bedrock were smaller than those of the specimen without raised bedrock (i.e. with deeper soil). Further, parametric studies using 2-dimensional finite element (FE) analysis were performed to investigate the effect of design parameters on the response of shallow soil with variable soil depths. For design parameters, the length of raised bedrock and the length of foundation slab were considered. Parametric study results indicated that when the shallow soil region is wide, the results are similar to those of a 1-dimensional soil column. However, when the shallow soil region is narrow, the 2-dimensional response is smaller than the 1-dimensional soil column response. This was also observed in the actual site model.

Submarine debris flows are events that occur with great frequency on a geological scale and can cause major damage to offshore structures or even loss of human life. Understanding the mechanisms involved in the development of a debris flow requires not only knowledge of soil mechanics, but also knowledge of fluid mechanics, since the incorporation of water during the flow causes changes in shear strength. Unlike soils, the shear strength of fluids is represented by mathematical models called rheological models. The objective of this paper is to propose a new rheological model capable of representing the changes caused by water entrainment into a submarine debris flow, by correlating it with the Liquidity Index of the soil. A rheological analysis of marine clay samples from the pre-salt layer has made it possible to represent the variation in strength due to water content. The influence of water content and velocity on flow behavior has also been studied through the analysis of centrifuge tests performed in a previous study.