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.

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.

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.