Tailing sand contains a large number of heavy metals and sulfides that are prone to forming acid mine drainage (AMD), which pollutes the surrounding surface environment and groundwater resources and damages the ecological environment. Microbially induced calcium carbonate precipitation (MICP) technology can biocement heavy metals and sulfides in tailing sand and prevent pollution via source control. In this study, through an unconfined compressive strength test, permeability test, and toxic leaching test (TCLP), the curing effect of MICP was investigated in the laboratory and the effect of grouting rounds on curing was also analyzed. In addition, the curing mechanism of MICP was studied by means of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM). The experimental results showed that MICP could induce calcium carbonate precipitation through relatively complex biochemical and physicochemical reactions to achieve the immobilization of heavy metals and sulfides and significantly reduce the impact of tailing sand on the surrounding environment.

Red-bed argillaceous siltstone is one of main types of rocks composing unstable slopes on both banks of water diversion project from the Yangtze to Huaihe River and is prone to deterioration after subjected to drying-wetting cycle conditions during water diversion project operation. The study of the damage degradation and the constitutive relationship of rocks subjected to drying-wetting cycle process is therefore of critical scientific importance. In this paper, laboratory tests were conducted to investigate the effect of drying-wetting cycles on the mechanical properties and microstructural characteristics. The experimental results show that the microstructure of the sample surface is no longer dense and uniform and the porosity of tested samples significantly increases with drying-wetting cycles increasing. After subjected to cycles of drying-wetting, the compaction stage of the stress-strain curve becomes longer with more pronounced nonlinear features, while uniaxial compression strength (UCS) and elastic modulus drop obviously. Combined with the evolution characteristics of microstructure found as the porosity grew, UCS and elastic modulus gradually decline. Additionally, from the perspective of energy analysis, the input energy density and dissipated energy density gradually extended with the increasing strain, and the elastic energy density increased first and then declined. As the number of drying-wetting cycles increases, the energy density of samples all present linear fell. Based on the evolution of dissipated energy, a new damage model of red-bed argillaceous siltstone subjected to drying-wetting cycles was established by introducing compaction coefficient. The coefficients of determination (⁠ $R2$⁠) of the constitutive model are always greater than 0.85, indicating that the proposed model is generally in good agreement with the experimental data under different drying-wetting cycles. This paper has specific research and reference value to understand the damage evolution characteristics of red-bed argillaceous siltstone under cyclic drying-wetting.

Microbial induced carbonate precipitation (MICP) is a natural bio-mediated process that has been investigated for soil stabilization and heavy metal immobilization in soil and groundwater. This study analyzed the effect and mechanism of MICP for the solidification/stabilization of tailings sand with multi-heavy metals. When the concentration of cementation solution (CS) is 1.0 mol/L and the optical density(OD₆₀₀) is 1.6, the unconfined compressive strength of tailings sand treated by MICP is the largest, and the solidification efficiency of heavy metals in tailings sand is also the highest. The macroscopic and microscopic observations reveal that the mechanism of MICP solidification of tailings is bacterial outer oxide, hydroxide, alkaline carbonate, and carbonate precipitation.

Excavation near or above existing shield tunnels often results in adverse impacts on tunnel stability. To ensure the serviceability of existing tunnels, this paper presents experimental and numerical studies with reference to a foundation pit case history excavated above twin-tube shield tunnels in soft soils. The experimental tests were firstly applied to study the deformation characteristics and structural response of the shield tunnels. Thereafter, an extensive numerical investigation was performed to determine the influence of some factors such as cover-to-excavation depth ratio, length-to-depth ratio, and unloading ratio on tunnel displacement behaviors. It was demonstrated that the tunnel heaves as the excavation proceeds, and heaves and horizontal displacements reach their maximum values when the excavation is finished. The earth pressure around the tunnels is symmetrically distributed in a gourd shape, with a larger reduction at the tunnel crown and invert and a smaller reduction at tunnel side walls. Additionally, the earth pressure at the tunnel crown and invert changes more significantly than that at other parts. The tunnel moment increment is significantly affected by the tunnel excavation depth. The axial force at or near the side walls of the tunnel is the most sensitive to the unloading effect induced by the excavation activity.