In order to estimate accumulated excess pore pressures in the soil around a cyclically loaded (offshore) foundation structure, cyclic laboratory tests are required. In practice, the cyclic direct simple shear (DSS) test is often used. From numerous undrained tests (or alternatively tests under constant-volume condition) under varying stress conditions, contour diagrams can be derived, which characterize the soil's behavior under arbitrary cyclic loading conditions. Such contour diagrams can then be used as input for finite element models predicting the load-bearing behavior of foundation structures under undrained or partially drained cyclic loading. The paper deals with the general behavior of a poorly graded medium sand in cyclic DSS tests under undrained loading conditions. The main objective of the research was to investigate and parametrize the soil's behavior and to identify possible effects of sample preparation. Numerous tests with varying cyclic stress ratios (CSR) and mean stress ratios (MSR) have been conducted. Also the relative density of the sand was varied. A new set of equations for a relatively easy handable mathematical description of the resulting contour plots was developed and parametrized. In the original tests, the sand was poured into the testing frame and carefully compacted to the desired relative density by tamping. In offshore practice, a preconditioning of a soil sample is usually realised by cyclic preshearing with a certain CSR-value or additionally by preconsolidation under drained conditions. By that, a more realistic initial state of the soil shall be achieved. In order to investigate the effect of such a preconditioning on the resulting contour diagrams, additional tests were conducted in which preshearing and preconsolidation was applied and the results were compared to the test results without any preconditioning. The results clearly show a significant effect of preshearing and an even more pronounced effect of preconsolidation for the considered poorly graded medium sand.

Most of the robust artificial intelligence (AI)-based constitutive models are developed with synthetic datasets generated from traditional constitutive models. Therefore, they fundamentally rely on the traditional constitutive models rather than laboratory test results. Also, their potential use within geotechnical engineering communities is limited due to the unavailability of datasets along with the model code files. In this study, the data-driven constitutive models are developed using only laboratory test databases and deep learning (DL) techniques. The laboratory database was prepared by conducting cyclic direct simple shear (CDSS) tests on reconstituted sand, that is, PDX sand. The stacked long short-term memory (LSTM) network and its variants are considered for developing the predictive models of the shear strain (gamma [%]) and excess pore pressure ratio (ru) time histories. The suitable input parameters (IPs) are selected based on the physics behind the generation of ru and gamma (%) of the liquefiable sands. The predicted responses of gamma (%) and ru agree well in most cases and are used to predict the dynamic soil properties of the PDX sand. The same modeling framework is extended for other sand and compared with existing AI-based constitutive models to verify its practical applicability. In summary, it is observed that though the trained models predicted the time histories of ru and gamma reasonably well; however, they struggled to predict the hysteresis loops at higher cycles. Therefore, more research is needed to verify and enhance the predictability of existing AI-based models in the future before using them in practice for simulating cyclic response.

Around the world severe damages were observed due to reliquefaction during repeated earthquakes, whereas precise understanding of its mesoscopic mechanism is not much discovered. Influence of these earthquakes on reliquefaction needs to be investigated to understand its significance in contributing to inherent sand resistance. In the present study, centrifuge model experiments were performed to examine the influence of foreshocks/aftershocks and mainshock sequence on resistance to reliquefaction. Two different shaking sequences comprising six shaking events were experimented with Toyoura sand specimen with 50 % relative density. Acceleration amplitude and shaking duration of a mainshock is twice that of foreshock/aftershock. In-house developed advanced digital image processing (DIP) technology was used to estimate mesoscopic characteristics from the images captured during the experiment. The responses were recorded in the form of acceleration, excess pore pressure (EPP), subsidence, induced sand densification, cyclic stress ratio, void ratio and average coordination number. Presence of foreshocks slightly increased the resistance against EPP before it gets completely liquefied during the mainshock. Similarly, aftershocks also regained the resistance of liquefied soil due to reorientation of particles and limited generation of EPP. However, application of mainshocks triggered liquefaction and reliquefaction and thus eliminated the beneficial effects achieved from the prior foreshocks. Reliquefaction was observed to be more damaging than the first liquefaction, meanwhile the induced sand densification from repeated shakings did not contribute to increased resistance to reliquefaction. The apparent void ratio estimated from the DIP technology was in good agreement with real void ratio values. Average coordination number indicated that the sand particles moved closer to each other which resulted in increased resistance during foreshocks/aftershocks. In contrast, complete liquefaction and reliquefaction have destroyed the dense soil particle interlocking and made specimen more vulnerable to higher EPP generation. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Methane gas hydrate-bearing sediments hold substantial natural gas reserves, and to understand their potential roles in the energy sector as the next generation of energy resources, considerable research is being conducted in industry and academia. Consequently, safe and economically feasible extraction methods are being vigorously researched, as are methods designed to estimate site-specific reserves. In addition, the presence of methane gas hydrates and their dissociation have been known to impact the geotechnical properties of submarine foundation soils and slopes. In this paper, we advance research on gas hydrate-bearing sediments by theoretically studying the effect of the hydromechanical coupling process related to ocean wave hydrodynamics. In this regard, we have studied two geotechnically and theoretically relevant situations related to the oscillatory wave-induced hydromechanical coupling process. Our results show that the presence of initial methane gas pressure leads to excessively high oscillatory pore pressure, which confirms the instability of submarine slopes with methane gas hydrate accumulation originally reported in the geotechnical literature. In addition, our results show that neglecting the presence of initial methane gas pressure in gas hydrate-bearing sediments in the theoretical description of the oscillatory excess pore pressure can lead to improper geotechnical planning. Moreover, the theoretical evolution of oscillatory excess pore water pressure with depth indicates a damping trend in magnitude, leading to a stable value with depth.

The present study aims to examine the behavior of sand reliquefaction phenomenon on gently inclined sloping ground subjected to repeated seismic events. The seismic sequence represents the combinations of foreshocks and aftershocks associated with mainshock events. Free field and pile group models were experimented with in a sloping ground with 5 degrees inclination using centrifuge modelling. A 2 x 2 pile group model was inserted in Toyoura sand, and results were compared with that with free field model ground. Tapered sinusoidal waveform was inputted at a constant 1 Hz shaking frequency, whereas the acceleration amplitude and shaking duration for the mainshocks were considered twice that of foreshocks and aftershocks. Two different seismic sequences with six shaking events were imparted to the model grounds to investigate the influence of slope and presence of pile group on sand reliquefaction behavior. The time history responses were recorded in the form of acceleration, excess pore pressure (EPP), bending moment, and lateral displacement and presented. The response indicates that sloping ground was stable under the action of foreshocks, whereas it collapsed during mainshocks, primarily due to liquefaction. The mainshock has transformed the gently inclined sloping ground to levelled ground model. This transformation has resulted in increased bending moment values in the pile group. Resistance to reliquefaction was smaller compared to first liquefaction, primarily due to change in soil state and increase in magnitude of anisotropy. Presence of slope has resulted in higher EPP response and bending moment values compared to levelled ground. GeoPIV analysis and visualization show the flow of sand particles from upside to downside due to lateral spreading at shallow depths that initiated the slope failure. The foreshocks and aftershocks are not very significant in increasing the resistance to reliquefaction. Meanwhile the presence of the pile group has reduced the EPP generation during repeated shaking events.

The prediction of time-dependent behavior of axial capacity for jacked piles are essential for coastal pile engineering. This study develops a numerical model to simulate the entire process of pile installation, soil consolidation, and loading, incorporating soil-pile interaction effects on excess pore pressure and effective stress distribution in the surrounding soil, which influence the bearing performance of jacked piles in saturated clay. The well consistency between the predictions from the presented approach and the experimental measurement data validate the applicability of the proposed model. The mechanism of set-up effects on the pile axial capacity is elucidated through the evolution of excess pore pressure. A parametric study is performed to assess the influence of the permeability coefficient (k) and length-to-diameter (L/De) ratio on the axial capacity of jacked piles. The findings demonstrate that the proposed model accurately predicts the set-up effects of jacked piles. Specifically, the permeability coefficient primarily impacts the rate of capacity increase, while the axial capacity exhibits a significant rise with an increase in L/De. The derived empirical formula can reasonably guide the design of the axial bearing capacity of piles in saturated clay.

The permeability in the natural clay layer is obviously anisotropic, and the flow of water in the pores often deviates from Darcian law. In order to analyze the effect of anisotropic non-Darcian flow on the two-dimensional consolidation of a saturated clay layer, the vertical and horizontal permeability laws of saturated clay were measured by the falling-head permeability test. It was found that the flow of water in both directions can be described by Hansbo's flow equation, and Hansbo's flow parameters in these two directions were obviously different. Then, the two-dimensional Terzaghi consolidation equations were modified considering the anisotropic Hansbo's flow and discretized into finite-element formulations. The validity of the numerical model was verified through comparison with the literature solutions. The effect of the anisotropic Hansbo's flow on the consolidation process of a two-dimensional saturated clay layer was analyzed under different lower boundary conditions. The numerical results indicated that in the initial stage of consolidation, the excess pore pressure is slightly concentrated in a specific area below the loading boundary. Moreover, variations in the lower boundary conditions have little effect on the distribution of excess pore pressure, and the influence of the different Hansbo's flow parameters in the vertical direction on the dissipation rate of excess pore pressure is not evident. However, in the middle and late stages of consolidation, the pore-water pressure with the permeable lower boundary condition is significantly lower compared to that with the impermeable lower boundary condition. Additionally, increasing the values of Hansbo's flow parameters in the vertical direction further impedes the dissipation rate of excess pore pressure, which in turn slows down the consolidation process of the clay layer.

Mixing discrete flexible fibres into sand may improve its liquefaction resistance during cyclic loading. Here, the benefits are demonstrated by performing undrained cyclic triaxial tests on fibre-reinforced samples in very loose and loose states. The development of a liquified state may be delayed when fibres are present. Here, the strain energy dissipation during loading, and liquefaction development, is focused on. The results show that strain energy continuously dissipates as undrained cyclic loading proceeds. The capacity energy, which coincides with a double amplitude axial strain of 5% or the unity of excess pore pressure ratio (ru\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${r}_{u}$$\end{document}), whichever occurs first, is increased by the inclusion of fibres. Under the two-way symmetrical cyclic loading, with a cyclic stress ratio of 0.2, the inclusion of fibres with a fibre content of 0.5% leads to the capacity energies of the samples in very loose and loose states increasing by 86.8 and 158.8%, respectively. The generation of pore pressure is closely related to the dissipated energy. The fibres alter the liquefaction responses of a sand skeleton in ways that depend on the applied loading conditions, and this depends on the extent to which the fibres are mobilized in tension during loading. When unities of ru\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${r}_{u}$$\end{document} are attained for fibre-reinforced sand samples, their states may vary greatly and remain far from liquefaction. A newly defined pore pressure ratio (ru & lowast;)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$({{r}_{u}}{*})$$\end{document} proves to be a better indicator of liquefaction in fibre-reinforced sand. A possible energy-based method, intended for practical use to assess liquefaction resistance of fibre-reinforced sand, and the margin of safety against liquefaction, is also presented.

Upon dynamic loading, saturated soils lose their strengths and undergo deformations resulting in volumetric-induced settlements that vary according to the excess pore pressure generation and dissipation variations. Traditionally, these settlements have been evaluated using standard charts based on one soil type and its relative density (RD). To assess these settlements, this study established a unique experimental methodology based on two laboratory testings: triaxial simple shear and piezoelectric ring actuator technique. Fifty-seven tests were performed on Ottawa F65 sand under strain-controlled cyclic and post-cyclic conditions. A chart was generated, revealing a relationship between the dissipated energy from cyclic loading and volumetric strain (e v ), based on the shear wave velocity as a controlling factor. This study was compared with previous studies to verify the compatibility of the proposed approach. Another novelty was revealed by studying e v variation with the dissipated pressure. This variation is presented in a post-seismic chart in which deformations are tracked based on the initial soil state and maximum excess pore pressure generation ratio ( Ru max ) at the end of the loading phase. For each RD, the soil is divided between liquefied and non-liquefied states according to a specific Ru max ( Ru maxtrigger point ). The calculation of the volume compressibility coefficient is proven to serve as a liquefaction-triggering criterion identifying the liquefied state.

This study investigates the rheological properties of saturated soft clay surrounding a tunnel using the generalized Voigt viscoelastic model. The model incorporates linear semi-permeability boundary conditions to describe the behavior of the clay. Furthermore, two-dimensional rheological consolidation control equations are derived based on the Terzaghi-Rendulic theory, considering the excess pore water pressure as a variable. To solve the equations, conformal transformation and separation of variables methods are employed, resulting in two independent equations representing the excess pore pressure in terms of time and space variables. The Laplace transformation and partial fractional summation method are then utilized to obtain the solution for excess pore pressure dissipation in the time domain. The reliability of the solution is verified by comparing it with the existing four-element Burgers and five-element model, both of which are derived from the generalized Voigt model. Furthermore, the influence of liner permeability, Kelvin body number, independent Newtonian dashpot viscosity coefficient, and tunnel depth on the dissipation and distribution of excess pore pressure is analyzed based on the established solutions. The findings indicate that a higher relative permeability of the liner and soil leads to an earlier onset of excess pore pressure dissipation and a faster dissipation rate. Increasing the number of Kelvin bodies results in slower dissipation rate. Moreover, larger independent viscous coefficients lead to smaller viscous deformation and faster dissipation rates. Additionally, greater tunnel depth prolongs soil percolation path, slowing down the dissipation of excess pore pressure. When the relative permeability coefficient is 0.01, the excess pore pressure gradually decreases with distance from the outer wall of the tunnel. However, when the relative permeability coefficient is 1, the excess pore pressure initially increases and then decreases with distance. As the relative permeability coefficient increases, the influence of the number of Kelvin bodies on the dissipation of super pore pressure diminishes, the variation in super pore pressure dissipation caused by different independent Newtonian dashpot viscosity coefficients gradually decreases, and the role of tunnel liners as new permeable boundaries within the soil layer is becoming increasingly prominent.