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In practical engineering, the magnitude of soil unloading rebound is closely related to the physical and mechanical properties of the soil. Therefore, there are significant differences in geological conditions among the different regions. As such, targeted research on the rebound law and calculation methods of foundation pits is needed. This article reports indoor experiments and numerical simulation methods which are used to study the trends and calculation methods of foundation pit rebound based on typical geological conditions in South China. Our findings are as follows. 1) At maximum consolidation stress ranging from 100 kPa to 400kPa, the maximum rebound rate of plain fill soil in typical soil layers is 0.0539-0.0704, the rebound rate of silty clay is 0.0373-0.0528, the rebound rate of coarse sand is 0.0296-0.0343, the rebound rate of gravelly cohesive soil is 0.0159-0.0305, the rebound rate of fully weathered granite is 0.0175-0.0344, and the rebound rate of strongly weathered granite is 0.0170-0.0379. 2) The rebound indices do not change with changes in the unloading ratio or initial consolidation stress. The rebound indices of the soil layer from top to bottom are 0.0143, 0.0119, 0.0077, 0.0096, 0.0083, and 0.0076, respectively, and a formula for calculating the rebound modulus of typical soil layers in South China was proposed. 3) The pore ratio of the soil after the end of the recompression process is lower than that which occurs after the first compression. The difference between the compression porosity ratio of the soil layer from top to bottom and the compression porosity ratio is 0.1, 0.08, 0.02, 0.06, 0.02, and 0.03, respectively. 4) The calculation of the depth of influence by the self-weight stress offset method is based on the theory of eliminating self-weight stress and unloading stress. The calculation depth is not affected by geological conditions, the formula for calculating the rebound modulus is consistent with the formula obtained from experimental research, and the calculation results are in good agreement with the numerical values. [ABSTRACT FROM AUTHOR]

• The effect of contamination on the microstructural characteristics is investigated. • The change in microstructural characteristics is highlighted via microscale tests. • The mechanical and microstructural properties present a good mutual correspondence. Soil contamination not only can cause environmental problems but also lead to a notable change in the mechanical properties of soil. Loess widely distributed over North-West (NW) China is featured with the metastable structure, and chemical contaminants produced especially during the rapid development of NW China in recent years seriously threaten the fragile loess environments. When exposed to chemical contaminants, the impacts on the microstructural characteristics of the loess and the resultant mechanical properties are deemed critical for land reclamation in NW China. In light of this, the microscale structural characteristics of the loess exposed to acetic acid, phosphoric acid, sodium hydroxide, and sodium sulfate respectively are studied using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy tests. Additionally, their resultant macroscale mechanical properties are determined by direct shear tests. The deterioration mechanism regarding the microscale structural characteristics when exposed to the contaminants is revealed, and the resultant macroscale mechanical properties present a good correspondence with the deteriorated microscale structural characteristics. The findings of this work provide some guideposts for contaminated land reclamation in NW China. [ABSTRACT FROM AUTHOR]

Inappropriate irrigation could trigger migration of heavy metals into surrounding environments, causing their accumulation and a serious threat to human central nervous system. Traditional site remediation technologies are criticized because they are time-consuming and featured with high risk of secondary pollution. In the past few years, the microbial-induced carbonate precipitation (MICP) is considered as an alternative to traditional technologies due to its easy maneuverability. The enzyme-induced carbonate precipitate (EICP) has attracted attention because bacterial cultivation is not required prior to catalyzing urea hydrolysis. This study compared the performance of lead (Pb) and copper (Cu) remediation using MICP and EICP respectively. The effect of the degree of urea hydrolysis, mass and species of carbonate precipitation, and chemical and thermodynamic properties of carbonates on the remediation efficiency was investigated. Results indicated that ammonium ion (NH 4 + ) concentration reduced with the increase in lead ion (Pb 2+ ) or copper ion (Cu 2+ ) concentration, and for a given Pb 2+ or Cu 2+ concentration, it was much higher under MICP than EICP. Further, the remediation efficiency against Cu 2+ is approximately zero, which is way below that against Pb 2+ (approximately 100%). The Cu 2+ toxicity denatured and even inactivated the urease, reducing the degree of urea hydrolysis and the remediation efficiency. Moreover, the reduction in the remediation efficiency against Pb 2+ and Cu 2+ appeared to be due to the precipitations of cotunnite and atacamite respectively. Their chemical and thermodynamic properties were not as good as calcite, cerussite, phosgenite, and malachite. The findings shed light on the underlying mechanism affecting the remediation efficiency against Pb 2+ and Cu 2+ ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Wang, Cheng, Xue, Rahman, Xie and Hu.)

Heavy metal contamination during the rapid urbanization process in recent decades has notably impacted our fragile environments and threatens human health. However, traditional remediation approaches are considered time-consuming and costly, and the effect sometimes does not meet the requirements expected. The present study conducted test tube experiments to reproduce enzyme-induced carbonate precipitation applied to lead remediation under the effects of urease concentration and a calcium source. Furthermore, the speciation and sequence of the carbonate precipitation were simulated using the Visual MINTEQ software package. The results indicated that higher urease concentrations can assure the availability of CO 3 2- during the enzyme-induced carbonate precipitation (EICP) process toward benefiting carbonate precipitation. The calcium source determines the speciation of carbonate precipitation and subsequently the Pb remediation efficiency. The use of CaO results in the dissolution of Pb(OH) 2 and, therefore, discharges Pb ions, causing some difficulty in forming the multi-layer structure of carbonate precipitation and degrading Pb remediation. The findings of this study are useful in widening the horizon of applications of the enzyme-induced carbonate precipitation technology to heavy metal remediation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Wang, Cheng, Xue and Hu.)

Given that acid-rich rainfall can cause serious damage to heritage buildings in NW China and subsequently accelerate their aging problem, countermeasures to protect their integrity and also to preserve the continuity of Chinese culture are in pressing need. Enzyme-induced carbonate precipitation (EICP) that modifies the mechanical properties of the soil through enhancing the interparticle bonds by the precipitated crystals and the formation of other carbonate minerals is under a spotlight in recent years. EICP is considered as an alternative to the microbial-induced carbonate precipitation (MICP) because cultivating soil microbes are considered to be challenging in field applications. This study conducts a series of test tube experiments to reproduce the ordinary EICP process, and the produced carbonate precipitation is compared with that of the modified EICP process subjected to the effect of higher MgCl 2 , NH 4 Cl, and CaCl 2 concentrations, respectively. The modified EICP, subjected to the effect of higher MgCl 2 concentrations, performs the best with the highest carbonate precipitation. The enhancement mechanism of carbonate precipitation is well interpreted through elevating the activity of urease enzyme by introducing the magnesium ions. Furthermore, the degradation of carbonate precipitation presents when subjected to the effect of higher NH 4 Cl concentration. The decreasing activity of urease enzyme and the reverse EICP process play a leading role in degrading the carbonate precipitation. Moreover, when subjected to the effect of higher CaCl 2 concentrations, the slower rate of urea hydrolysis and the decreasing activity of urease enzyme are primarily responsible for forming the "hijacking" phenomenon of carbonate precipitation. The findings of this study explore the potential use of the EICP technology for the protection of heritage buildings in NW China., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Hu, Cheng, Wen and Yuan.)