The foundation soil below the structure usually bears the combined action of initial static and cyclic shear loading. This experimental investigation focused on the cyclic properties of saturated soft clay in the initial static shear stress state. A range of constant volume cyclic simple shear tests were performed on Shanghai soft clay at different initial static shear stress ratios (SSR) and cyclic shear stress ratios (CSR). The cyclic behavior of soft clay with SSR was compared with that without SSR. An empirical model for predicting cyclic strength of soft clay under various SSR and CSR combinations was proposed and validated. Research results indicated that an increase of shear loading level, including SSR and CSR, results in a larger magnitude of shear strain. The response of pore water pressure is simultaneously dominated by the amplitude and the duration of shear loading. The maximum pore water pressure induced by smaller loading over a long duration may be greater than that under larger loading over a short duration. The initial static shear stress does not necessarily have a negative impact on cyclic strength. At least, compared to cases without SSR, the low-level SSR can improve the deformation resistance of soft clay under the cyclic loading. For the higher SSR level, the cyclic strength decreases with the increase of SSR.

Cyclic spherical stresses are prevalent in dynamic stress fields and significantly influence the dynamic behavior of loess, a material characterized by high compressibility and anisotropy. Previous research has primarily focused on shear stresses, often overlooking the impact of spherical stresses. This study investigated the deformation induced by cyclic spherical stress under different initial states. Irreversible and reversible components were identified from both volumetric and shear strains, and their variation patterns were analyzed. Shear strain is found to be generated by the material's anisotropy. The results indicate that the volume of the sample shrinks significantly under cyclic spherical stress, with irreversible volumetric strain increasing nonlinearly as the number of cycles increases. Irreversible shear strains can be categorized into two types based on their formation mechanisms. The first is when significant initial anisotropy leads to radial deformation greater than axial deformation under spherical stress, resulting in shear strain increasing in the negative direction. As consolidation stress increases, the initial anisotropy gradually diminishes. The second is when stress-induced anisotropy results in positive shear strain because consolidation deviatoric stress contributes to an increase in shear strain in the positive direction. As the stress ratio rises, the induced anisotropy is further enhanced. The axial reversible strain of the sample is minor, and the reversible components of volumetric and shear strains primarily arise from radial contraction and expansion. As the spherical stress increases, the sample volume shrinks (positive volumetric strain), whereas the initial anisotropy leads to negative shear strain, resulting in opposite signs. Finally, a method for predicting irreversible strain under cyclic spherical stress is established based on a memoryless geometric distribution.

The present experimental study evaluates the overburden correction factor (K6) of different pond ash samples under earthquake loading for liquefaction analysis. A series of 54 stress-controlled cyclic simple shear tests was conducted on pond ash specimens at different overburden pressures and cyclic stress ratios. Cyclic resistance ratio (CRR) was evaluated for each pond ash sample at different overburden pressures using two criteria based on maximum excess pore water pressure and double amplitude shear strain to evaluate the K6. The K6 values obtained for the pond ash were compared with the K6 values for natural soils (clean sand and sand-silt mixtures). The cyclic resistance ratio (CRR) and K6 values were observed to decrease with an increase in overburden pressure from 50 kPa to 100 kPa, and a further increase in overburden pressure to 150 kPa led to an increase in CRR and K6 values for pond ash specimens with fine particles dominated matrix. However, an opposite trend was observed for pond ash specimens with coarse particles-dominated matrix. The unique response of K6 values for pond ash was found to be significantly different from the already available K6 response for natural cohesionless soil (clean sand and sand-silt mixtures) as it unavoidably included the effect of OCR and void ratio along with the vertical overburden pressure.

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.

The liquefaction and weakening of saturated sands under cyclic stress loading is a major concern in earthquake engineering. This study proposes a model based on initial cyclic shear strain (gamma c,i) to predict the excess pore pressure generation in undrained saturated sands. Here, gamma c,i is defined as the average cyclic shear strain prior to the significant accumulation of excess pore pressure. To calibrate and validate the model, a series of undrained stress-controlled cyclic triaxial (CTX) tests were conducted on Fujian sand with 10 % Kaolin clay (FS-10) and Silica sand no.7 with 5 % Kaolin clay (SS7-5). The FS-10 and SS7-5 specimens displayed typical flow liquefaction and cyclic mobility as they approached initial liquefaction. A critical excess pore pressure ratio (ru,c) is introduced to characterize the effects of liquefaction failure modes on excess pore pressure generation. The model also incorporates reduction factors related to small-strain secant shear modulus and reference shear strain to account for variations in calculating gamma c,i. Ultimately, the initial cyclic shear strain-based model exhibited a strong correlation with experimental data under different confining pressures and loading cycles. In addition, it provides a critical initial cyclic shear strain for assessing soil liquefaction in engineering practices, particularly for improved ground with complex stress states.

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.

Seismic events and wave action can induce volumetric strain (ev) accumulation in saturated sandy soils, leading to damage to the ground surface and structures. A quantifiable relationship exists between the generation of ev in sandy soils under drained conditions and the development of pore water pressures under undrained conditions. In this study, the impact of relative density (Dr), cyclic stress path, and stress level on the characteristics of volumetric strain (ev) generation in saturated coral sands (SCS) was evaluated through drained tests employing various cyclic stress paths. The test findings demonstrate that the rate of ev accumulation in SCS is notably affected by the cyclic stress path. The rise in peak volumetric strain (evp) in SCS, as a function of the number of cycles, conforms to the arctangent function model. The unit cyclic stress ratio (USR) was employed as an indicator of complex cyclic loading levels. It was determined that coefficient (evp)u is positively correlated with USR at a specific Dr. At the same Dr, coefficient CN1 exhibits a positive correlation with USR, while coefficient CN2 displays a negative correlation with USR, following a power-law relationship. Irrespective of cyclic loading conditions, evp rises with an increase in generalized shear strain amplitude (yga). A power function model was established to represent the relationship between evp and yga. The coefficient 41 decreases as Dr increases. Comparisons were drawn between evp and yga for Ottawa sand and SCS. The results indicate that, as Dr of Ottawa sand increases from 30 % to 70 %, the coefficient 41 decreases from 1.54 to 0.73, representing a reduction of approximately 53 %. In contrast, under identical conditions, the coefficient 41 of SCS exhibits a less pronounced decrease, from 1.16 to 0.79, corresponding to a reduction of roughly 32 %. These observations suggest that variations in Dr have a more substantial impact on generating evp in Ottawa sand compared to SCS.

Slope stability analysis constitutes a crucial component of the operational procedures involved in open-cast mining. A slope failure adjacent to an active mining site could give rise to severe societal, economic, and safety implications of a grave nature. It is widely recognized that multiple parameters, such as the type of minerals, orientation of joints, precipitation patterns, pore water pressure, cohesive properties, and the angle of internal friction exhibited by the rock masses, exert influence over the stability of a slope. Presently, the design of slopes primarily relies on empirical knowledge gained from practical field experience. The objective of this paper is to employ numerical modelling techniques to analyse a of the slope characterized by a series of terraced benches and diverse layers of soil featuring varying properties. The numerical analysis is performed using FLAC (Fast Lagrangian Analysis of Continua), a software developed by Itasca International. This analysis aims to determine the Factor of Safety, Pore Pressure, Saturation, Stress, Strain Rate, Strain Increment, Velocity Vector, and Displacement Vector. Furthermore, the investigation examines the outcomes obtained during both dry and wet stages. The wet stage encompasses two infiltration scenarios, namely, a prolonged period of light rainfall lasting four months and an intense rainstorm lasting four days. The results also include a reduction in saturation and shear strain rate when the water is prevented from infiltrating the horizontal surfaces of the whole slope.

Offshore wind turbines are subjected to more significant wave and wind environmental loads at extreme weather conditions, making subsoil experience various loading stages with different amplitudes. To investigate the coupling effect of both cyclic shear stress ratio (CSR) and stage amplitude ratio (Ar) between normal and extreme weather conditions, a series of bi-directional simple shear tests with five different Ar and three CSR values were conducted on marine sand using the variable-direction dynamic cyclic simple shear (VDDCSS) apparatus. In the tests, soil samples were compacted under vertical stress and then sheared in undrained conditions by applying two shear stresses acting in different horizontal directions. Test results indicated that the cyclic strain, pore water pressure ratio, and cyclic strength were significantly determined by the value of stage amplitude ratios and the CSRs: at the same CSR, cyclic strains, and pore water pressure increased while cyclic strength decreased with the Ar. Comparing the test data between various cyclic stress ratios found that the CSRs can accelerate shear strains, pore pressure accumulation, and cyclic strength attenuation.

The generation mechanism of pore pressure plays an essential role in understanding the liquefaction behavior of sand under cyclic loading. Extensive undrained simple shear tests were undertaken to study the pore pressure and shear strain development characteristics of calcareous sand reinforced by fibers. The results show that the deformation patterns of the tested calcareous sand gradually shift from brittle to ductile failure as fiber content increases. The mechanism of pore pressure generation in calcareous sand subjected to cyclic loading is quite distinct from that of siliceous sand, exhibiting more pronounced accumulation in the initial stage of cyclic loading. Fiber reinforced calcareous sand exhibits reverse shear contraction behavior when liquefaction is imminent. A remarkable finding is the establishment of a unique correlation between pore pressure ratio and shear strain, irrespective of the fiber reinforcement. Consequently, a shear strain-based pore pressure generation model of reinforced calcareous sand is then developed to predict the pore pressure built-up trend under varying fiber content and length conditions. This model is also applicable to various testing conditions and soil types.