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.

In this study, the soil around a granular column is considered as a drain influence zone, in which horizontal permeability coefficient changes linearly with radial distance. And so, it is only a special case that the soil around a column is traditionally divided into smeared and undisturbed zones with constant horizontal permeability coefficient. The differential governing equations are established on the basis of gradual change in horizontal permeability of soft soil caused by disturbance during granular column installation, and the analytical solution is obtained and then applied to investigate the influence of the permeability change on the consolidation behavior. It shows that the influence of disturbance on consolidation is significant. The greater the disturbance is, the slower the consolidation is.

Long-term static leaching experiments were conducted to investigate characteristics of magnesium phosphate cement (MPC) solidified/stabilized Zn-contaminated soil under impact of acid rain. Effects of initial pH values of acid rain, binder agent types and compositions, as well as curing age on strength and leaching characteristics of the sample were analyzed. Standard sand was used as raw material, with the content of cement at 15%. Our study used two types of MPC with MgO/KH₂PO₄(M/P) ratio of 3:1 and 6:1 (respectively referred to as M3 and M6), and also ordinary Portland cement with content at 15% (referred to as C15) as test control. Experimental results show that acid rain with pH = 2 has the greatest weakening effect on unconfined compressive strength (q_u) of the sample, while with pH = 4 and 7 such weakening effects on q_u are similar. Research findings also indicate that M6 is the most effective in immobilizing Zn-spiked soils, M3 is next and C15 is the least. The effect of Zn²⁺ on hydration of MPC is much lower than that of C15. Precuring method can improve q_u of the MPC-solidified samples and its resistance to acid rain. Compared with non-renewal, replacing acid rain leachant at designated intervals decreases q_u of the sample.

Photothermal therapy (PTT) based on semiconducting polymer nanoparticles (SPNs) is a promising strategy to treat solid tumors, but its ability to combine with chemotherapy for immune remodeling to efficiently suppress metastatic cancers has rarely been studied. Here, we demonstrate that PTT combined with chemotherapy can efficiently elicit immunity to suppress metastatic tumor growth. Specifically, we rationally designed a new SPN (PDPSe NPs) as a photothermal agent for PTT with a large mass extinction coefficient in the near-infrared region (e.g., 44.9 L g⁻¹ cm⁻¹ at 808 nm), high photothermal conversion efficiency (62.5%) and excellent biocompatibility. A hypoxia-activated anti-tumor drug, tirapazamine (TPZ), was selected for chemotherapy. Strikingly, the combination therapy not only induced tumor cell death in the primary tumor, but also effectively suppressed the growth of distant tumors (mimicking metastatic tumors) without PTT. Importantly, the combined therapies exhibit synergistic effects on immune remodeling. Immunofluorescence data suggest that the inhibition of metastatic tumor growth is attributed to the immune remodeling triggered by PTT and chemotherapy. This work demonstrates a new paradigm of utilizing PTT together with hypoxia-activated drugs to effectively retard metastatic tumor growth.