Soft soil subgrades often present significant geotechnical challenges under cyclic loading conditions associated with major infrastructure developments. Moreover, there has been a growing interest in employing various recycled tire derivatives in civil engineering projects in recent years. To address these challenges sustainably, this study investigates the performance of granular piles incorporating recycled tire chips as a partial replacement for conventional aggregates. The objective is to evaluate the cyclic behavior of these tire chip-aggregate mixtures and determining the optimum mix for enhancing soft soil performance. A series of laboratory-scale, stress-controlled cyclic loading tests were conducted on granular piles encased with combi-grid under end-bearing conditions. The granular piles were constructed using five volumetric proportions of (tire chips: aggregates) (%) of 0:100, 25:75, 50:50, 75:25, and 100:0. The tests were performed with a cyclic loading amplitude (qcy) of 85 kPa and a frequency (fcy) of 1 Hz. Key performance indicators such as normalized cyclic induced settlement (Sc/Dp), normalized excess pore water pressure in soil bed (Pexc/Su), and pile-soil stress distribution in terms of stress concentration ratio (n) were analyzed to assess the effectiveness of the different mixtures. Results indicate that the ordinary granular pile (OGP) with (25 % tire chips + 75 % aggregates) offers an optimal balance between performance and sustainability. This mixture reduced cyclic-induced settlement by 86.7 % compared to the OGP with (0 % TC + 100 % AG), with only marginal losses in performance (12.3 % increase in settlement and 2.8 % reduction in stress transfer efficiency). Additionally, the use of combi-grid encasement significantly improved the overall performance of all granular pile configurations, enhancing stress concentration and reducing both settlement and excess pore water pressure. These findings demonstrate the viability of using recycled tire chips as a sustainable alternative in granular piles, offering both environmental and engineering benefits for soft soil improvement under cyclic loading.

Increasing demand on clean energy leads to the expanded construction of offshore wind turbines (OWT) worldwide. Different types of foundations of OWTs includes gravity, jackets, monopiles etc. When functioning, OWTs face severe conditions with complex loadings (e.g. varying loading amplitudes and loading frequencies). In this study, the influence of the loading amplitude and loading frequency on the lateral displacement of monopiles in marine clay was investigated by conducting 1-g physical model tests at a scale of 1:30. The p-y curves at different depths were derived as well from the recorded moment distribution along the monopile. According to the results, the lateral displacement increases with the loading amplitude and frequency and the monopiles experience response of shakedown under cyclic loading. The lateral displacement after N cycles is related to the initial displacement via an extended logarithmic function. Besides, the p-y curves available in literature underestimate the soil resistance but hyperbolic functions provide comparatively closer predictions.

This article experimentally evaluates the influence of shearing rate on the monotonic and cyclic response of isotropically-consolidated samples of Malaysian kaolin. On the one hand, a series of undrained monotonic triaxial tests were performed with varying shearing displacement rate. On the other hand, undrained cyclic triaxial tests were conducted considering different deviatoric stress amplitudes and loading frequencies. The well-known soil rate-dependency under monotonic loading was confirmed up to a displacement rate threshold. The experimental results under cyclic loading suggest that for the given loading frequency, the variation of the deviatoric stress amplitude remarkably influences the strains and pore water pressure accumulation rates. In addition, the results suggest that depending on the loading frequency different shapes of mobilized effective stress loops are obtained. Larger loading frequencies lead to banana-shaped effective stress loops, while smaller frequencies reproduce eight-shaped effective stress loops. Furthermore, higher loading frequencies result in a larger number of cycles required to reach failure conditions. The reasons for the observed differences in the behavior are thoroughly analyzed and discussed.

A series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency on the liquefaction characteristics of saturated sand using the hollow cylinder apparatus. The test results show that the dilative and contractive tendencies of various saturated sands are not only related to the physical properties of sand, but also affected by loading frequency. Under low-frequency loading, the saturated sand has a dilative behaviour, excess pore water pressure fluctuates after initial liquefaction and soil maintains the ability to resist liquefaction to some extent after the initial liquefaction. The liquefaction mode in terms of stress-strain relationship generally performs as the cyclic mobility. However, under the high-frequency loading, the saturated sand has a contractive behaviour, excess pore water pressure generally keeps stable after the initial liquefaction. The liquefaction mode in terms of stress-strain relationship generally exhibits as cyclic instability. The deformation caused by low-frequency loading is significantly larger compared with that caused by high-frequency loading. At higher loading frequencies, the phase transformation stress ratio increases with the increase of loading frequency, and gradually approaches the failure stress ratio.

In marine environments, cyclic loads induced by earthquakes can lead to complex soil responses in marine coral sand. Waves and storms, often at different frequencies, can also contribute to these responses. These factors can finally contribute to instability or failure of offshore structures. To better understand the effect of loading frequency on the dynamic properties of marine coral sand, a series of cyclic triaxial tests on saturated coral sands were carried out. These tests were performed with different gradations at different loading frequencies and loading modes. A GDS dynamic triaxial instrument was used for the tests. The experimental results demonstrate that loading frequency has a significant effect on the cyclic response of coral sand. The maximum shear modulus of saturated coral sand rises with increasing loading frequency. The cyclic strength of saturated coral sand also increases with loading frequency. A strong linear relationship exists between the maximum shear modulus and cyclic strength. This suggests the existence of a cyclic yield strain that is relatively insensitive to loading frequency. Loading frequency significantly affects the axial strain development of saturated coral sand under diverse loading modes. Three stages of axial strain development were identified employing incremental strain analysis. Based on these findings, a new model for axial strain development is proposed, the accuracy of this model is verified by fitting it to the data from this study and existing literature.

The dynamic deformation characteristics of saturated sands are considerably influenced by the loading frequency (f). Nevertheless, the effect of f on the deformation behavior of saturated coral sand (CS) has not been comprehensively investigated. This study aims to investigate how frequency (0.01-4Hz) affects the shear modulus (G) and damping ratio (lambda) characteristics of CS through a series of cyclic shear tests. The experimental results demonstrate that, under consistent initial conditions, both the strain-dependent G and lambda increase as f increases. Moreover, there is a linear relationship between the maximum shear modulus (G0) and small strain damping ratio (lambda min) with ln(f). Specifically, the regularized G of CS remains unaffected by variations in f. To facilitate the prediction of G in CS at different f, we propose a prediction equation that integrates the revised Hardin's model and Davidenkov skeleton curve. Besides, a power function expression is suggested for lambda-lambda min versus G/G0 to predict lambda in CS at different f. The revised equations for G and lambda are validated using experimental data from natural sands in the literature, confirming their suitability for evaluating strain-dependent G and lambda values of natural sandy soils over a wide strain range.

The kinematic interaction between piles under seismic loading has been extensively studied from analytical, experimental, and numerical perspectives. Of note, within numerical modeling, the majority of the existing literature relies on simplified approaches for characterizing the soil-pile interaction, which leads to the requirement for more reliable and comprehensive research. In this paper, using FLAC3D, the seismic response of the soil-pile system was investigated with a set of fully nonlinear three-dimensional (3D) numerical analyses in the time domain. This model simulated the soil strength and stiffness dependency on the stress level and soil nonlinear behavior under cyclic loading. The Mohr-Coulomb (M-C) constitutive model described the soil's mechanical behavior, which was used with additional hysteretic damping to suit the dynamic behavior. In the framework of a parametric study, the effects of loading frequency on the response of a soil-pile system that was subjected to seismic loading were studied. The results showed that the pile response and soil characteristics, as well as the natural frequency mode of the system's dynamic behavior, are strongly affected by the frequency of the seismic loading. Therefore, the bending moment and lateral displacement along the length of a pile increase as the loading frequency approaches the natural frequency of the system. In addition, when the loading frequency reaches a threshold value far from the fundamental frequency of the system, the effect of loading frequency on the soil-pile system response becomes negligible. In addition, the relationship between the pile diameter and maximum pile bending moment at different loading frequencies is affected by the soil properties.

Structured soft clay is characterised by high sensitivity and compressibility and accumulates excessive deformation under long-term dynamic loads, e.g., traffic loads, which likely threatens the service performance of overlying structures. In this work, to model the long-term mechanical behaviour of structured soft clay and efficiently capture its structural degradation, a new constitutive model was developed. The structural properties of soft clay, i.e., high yield strength and cohesive strength, were considered by a proposed yield surface, with their evolutions related to the combined plastic volumetric and deviatoric strains. The cyclic response of clay to undrained conditions was described through bounding surface theory. Moreover, the influence of the loading frequency on the dynamic response of clay was incorporated into the plastic modulus, and the softening effect caused by the generated excess pore water pressure (EPWP) was described by the shrinkable yield surface. Model validation was then carried out by reproducing both the accumulated strains and EPWPs of five types of reconstituted and structured soft clay. The acceptable consistency between the simulated results and experimental data and the independent and physical meaning of the featured model parameters confirmed the efficiency of the proposed model. More importantly, the evolution of the structural internal variables S-i and p(t)' with the development of plastic strains effectively represented the structural destruction process of soft clay under long-term cyclic loading conditions.

To investigate the effects of cyclic loading frequency (f) and loading patterns (90 degrees jump of principal stress, JPS, and continuous rotation of principal stress, CRPS) on the stiffness characteristics of saturated marine coral sands, a series of undrained cyclic shear tests were conducted. pi-plane is introduced as the analytical plane. We propose generalized deviator strain evolution (zeta q) to quantify the evolution of global strain, and introduce generalized dynamic modulus (K) to evaluate the soil's global stiffness. K and maximum generalized dynamic modulus (K0) exhibited a strong correlation with loading direction angle (alpha sigma), maximum loading direction angle (alpha sigma max), and f. Both patterns showed an increase in K0 with increasing f. Under JPS, the K0 initially decreased and then increased as alpha sigma increased, reaching its minimum value at alpha sigma = 45 degrees. Normalizing the effect of f and alpha sigma, we establish a unified empirical formula for K0. Under CRPS, K0 continuously decreased with increasing alpha sigma max. The global level of K0 is higher under CRPS compared to JPS. Additionally, the K/K0 curve was significantly influenced by alpha sigma but remained insensitive to f. A modified generalized Davidenkov model was developed to describe the recession properties of marine coral sands over a wide strain range.

Accurate prediction of excess pore water pressure (EPWP) generation in saturated sandy soils remains one of the most challenging issues in sandy site responses to strong earthquakes and extreme marine environments. This paper presents experimental results of undrained and drained multidirectional cyclic hollow cylinder (MCHC) tests on saturated coral sandy soils under various cyclic loadings. The results show that threshold generalized shear strain gamma ga,th, below which EPWP and volumetric strain can be neglected, is an inherent property depending only on the soil type and initial state. Furthermore, there exists a virtually unique form of relationships between the generalized shear strain amplitude (gamma ga) and the cumulative dissipated energy per unit volume of soil (Wc) at different relative density (Dr), irrespective of drainage conditions and cyclic loading conditions. These findings highlight the fundamental mechanism for cyclic deformation behavior and the uniqueness of correlations among rup (peak EPWP ratio), epsilon vp (peak volumetric strain), and gamma ga of saturated sandy soil at the similar Dr, regardless of cyclic loading conditions. Based on these findings, a novel unified model of gamma ga-based cyclic shear-volume coupling and EPWP generation is established, which is independent of cyclic loading conditions over a wide loading frequency range. Then the applicability of the proposed model is validated by the experimental data of the same tested coral sandy soil and siliceous Ottawa sand, as well as the data of siliceous fine sands in previous work. It is found that the proposed model surpasses the existing strain- and stress-based models in accurately predicting EPWP generation under complex cyclic loadings, which can offer new insights into the mechanisms of the EPWP generation in saturated sandy soils.