Calcareous sand is a special marine soil rich in calcium carbonate minerals, characterized by brittle particles. It is, therefore, widely used as a filling material in the construction of islands and reefs. In this study, a series of cyclic tri-axial tests were conducted on calcareous sand taken from a reef in the South China Sea under different confining pressures and cyclic stress ratio (CSR). Then, applying the shakedown theory, the cumulative deformation of calcareous sand under a long-term cyclic load of aircraft was evaluated. Results showed that with the increase in the effective confining pressure, the stress–strain curves of calcareous sand showed a change from the strain-softening to the strain-hardening state; the volumetric strain of calcareous sand showed a change from shear shrinkage and then shear expansion to continuous shear shrinkage. Calcareous sand showed three different response behaviors under cyclic load: plastic shakedown, plastic creep and incremental plastic failure. With the plastic strain rate as the defining index, this study determined the critical CSR of calcareous sand under different shakedown response statuses and found them to increase with the effective confining pressure. The empirical formula for critical stress was established based on the fitting analysis of critical CSR under different confining pressures, taking the confining pressure as the variable. At the early stage of the cyclic load, calcareous sand samples were under compression. When the resilient modulus grew rapidly and the number of loading cycles continued to increase, the particles of calcareous sand samples were crushed, causing the fine particles to fill the voids among coarse particles, further compacting the samples and increasing the resilient modulus of calcareous sand samples. Hardin’s breakage potential model was adopted to quantitatively describe the particle breakage of calcareous sand samples before and after tests. The results indicated that calcareous sand samples produced obvious particle breakage when the CSR was small. As the CSR increased, the extent of the breakage of the sample particles first increased and thereafter stabilized. This study provides a theoretical reference for the assessment of the dynamic stability of calcareous sand subgrade subjected to traffic loads.

Pile-supported embankments are widely used in foundation treatments, owing to their safety, efficient construction, and economy. The soil-arching effect is a key load-transferring mechanism in a pile-supported embankment, and it reduces the even settlement on the embankment surface. In recent years, researchers and engineers have conducted extensive research on the soil-arching phenomenon in pile-supported embankments. This paper reviews relevant studies on the effect of soil arching in pile-supported embankments in order to better understand the mechanism and influencing factors of the distribution of the arching effect. First, the development history of the practice and theory related to pile-supported embankments is discussed. This is followed by a review of theoretical studies on the soil-arching effect, load distribution and soil deformation on pile-supported embankments (with and without geogrid reinforcement), and structures and factors influencing soil arching. The results of these studies are summarized, and finally, topics for future research are suggested, providing references for the design and maintenance of civil infrastructure.

Biaxial geogrid in current research is oversimplified, and the three-dimensional orthotropic nature of the biaxial geogrid has not been fully understood in numerical investigations. A comparative study on three modeling approaches for the biaxial geogrid is presented in this paper, including the isotropic membrane model, the orthotropic membrane model, and the truss element model. It shows that the orthotropic membrane model yields practically identical results of the maximum geogrid tension when compared with the truss element model, whereas the isotropic membrane model tends to yield values that are approximately 33% larger. A parametric study shows that the pile spacing has the strongest influence on the maximum geogrid tension. The comparison of four analytical methods with the orthotropic membrane model shows that the British standard (BS) 8006 (published in 2010) and EBGEO (published in 2011) methods greatly overestimate the geogrid tension, while the method presented by Zhuang et al. (published in 2014) results in closer agreement.