Post-grouted piles, as a foundation form for large-span and large-scale structures on calcareous sand, are expected to provide a high bearing capacity, but research on the response of post-grouted piles subjected to axial load in calcareous sand is still in the exploratory stage. In this paper, a model test is constructed for static pressure piles in calcareous sand under axial loading. The response of axial compressive piles, with and without post-grouting, in calcareous sand were investigated, and the test results were compared with those of axial compressive piles, with and without post-grouting, in siliceous sand. The influence of post-side-grouting on the response of a single pile subjected to axial compressive load in calcareous sand and its bearing mechanism were further analyzed. The results show that the change in shaft resistance, caused by the lateral extrusion of calcareous sand, is less than the negative effect caused by particle breakage during pile driving, so single piles without post-grouting in calcareous sand exhibit weaker axial bearing behavior than that in siliceous sand. A single pile with post-side-grouting in calcareous sand can provide a higher bearing capacity by increasing the shaft resistance and tip resistance compared with a single pile without post-side-grouting, and the increased ratio of the bearing capacity of piles, after grouting in calcareous sand, is better than that of piles in siliceous sand. Post-side-grouting can not only strengthen the surrounding soil by the solidification effect of injected cement grout, but it can also have a strengthening effect on the tip resistance. In addition, ideal-geometry grouting has more obvious advantages in improving the bearing behavior of pile foundations than annular point grouting, and higher stability in improving the bearing properties of pile foundations is evident for ideal-geometry grouting. Therefore, it is suggested that a directional grouting device should be adopted in actual projects in the future to form a more stable pile-soil interaction system and to expand the application prospect of pile foundations in calcareous sand.

Zn is a toxic heavy metal that seriously endangers human health and ecological stability. For a long time, traditional remediation techniques have been used to remediate Zn-contaminated soil prone to other problems such as secondary contamination. In recent years, due to the great danger posed by Zn pollution, there has been an increasing interest in applying eco-friendly and sustainable methods to remediate Zn-contaminated soil. Therefore, in this study, microbially induced calcium carbonate precipitation (MICP) technology was used to bioremediate zinc ions by transforming ionic heavy metals into insoluble solid-phase minerals. Through the unconfined compressive strength (UCS) test, direct shear (DS) test, and penetration test (PT), the results showed that the unconfined compressive strength of the treated specimens increased by 187.2~550.5%, the cohesion increased significantly compared with the internal friction angle of specimens, and the permeability coefficient can be reduced by at least one order of magnitude. During the treatment of Zn pollutants, the mobility of heavy metal zinc ions was significantly reduced, the percentage of exchangeable state Zn content was significantly reduced, and the leaching concentration of zinc ions in Zn-contaminated soil was reduced to about 20 mg/L, which was significantly lower than the limit in the standard (100 mg/L). These results were further confirmed by scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, which indicated coprecipitation of calcium carbonate (CaCO₃) and ZnCO₃. The microbial solidification/stabilization of Zn-contaminated soil was most effective when the curing age of 28 d, the cementation solution concentration of 1 mol/L, and the cementation solution ratio of 1:2. Therefore, the bio-immobilization of zinc ions by MICP has the potential for application as a low-cost and eco-friendly method for heavy metal remediation.

Developing an analytical solution for the consolidation of unsaturated soils remains a challenging task due to the complexity of coupled governing equations for air and water phases. This paper presents an equal‐strain model for the radial consolidation of unsaturated soils by vertical drains, and the effect of drain resistance is also considered. Simplified governing equations are established, and an analytical solution to calculate the excess pore‐air and pore‐water pressures is derived by using the methods of matrix analysis and eigenfunction expansion. The average degrees of consolidation for air and water phases and the ground surface settlement are also given. The solutions of the equal‐strain model are verified by comparing the proposed free‐strain model with the equal‐strain model, and reasonably good agreement is obtained. Moreover, parametric studies regarding the drain resistance effect are graphically presented.

The artificial ground freezing method has been widely used in shield tunneling breakthrough working shafts. The freezing effect was mainly considered in the previous research, and the heat generation of the shield machine was not considered, which has great influence in actual engineering. In this paper, a coupling calculation model, considering phase change latent heat, is establishes that by containing the freezing process and heat generation of the shield machine, the model is verified. A numerical simulation is carried out for several working conditions that may occur in actual projects, and the following conclusions are obtained. Although the heat dissipated by the normal tunneling of the shield machine will melt the frozen soil curtain that originally meets the design requirements, the thickness of the frozen soil curtain after melting cannot reach the initial design, though it is still within the safe range. In the process of a continuous rotation working condition, the bottom and sides of a cup-shaped frozen soil curtain are partially melted in the early 6 day stay of the shield machine, and the thickness is reduced to a relatively stable value of 0.8 m. In a temporary shutdown working condition, when the contact surface temperature between the shield machine shell and the frozen soil drops to −12 °C after almost 4 days of shutdown, the shield machine may not keep tunneling forward due to the freezing effect. The research results will benefit the freezing design and management of the shield tunneling breakthrough working shaft under extreme conditions.