The research on the deformation of soil mass and ground connection walls is not sufficiently thorough due to the huge risk of deep excavation in soft soil areas. In this paper, finite element software is used to numerically simulate a symmetrical foundation pit in Suzhou, and the reliability is verified by on-site measured data. The purpose of this study is to investigate the deformation mechanism of the enclosure structure and surrounding soil during the excavation of soft soil foundation pits, and to carry out sensitivity analysis. The results show that the maximum subsidence of the surface is 21.25 mm, the maximum horizontal displacement of the underground diaphragm wall is 9.45 mm, and the maximum uplift of the pit bottom is 21.46 mm. By changing the soil layer properties (the elastic modulus, cohesion, and internal friction angle) and the insertion ratio of the diaphragm wall, the maximum horizontal displacement of the diaphragm wall is more easily affected than the maximum settlement of the surface. Based on different research results, the maximum land subsidence and maximum horizontal displacement of the support structure are 0.313–0.060% and 0.070–0.250% of the maximum excavation depth, respectively. Finally, the simulation may have some applicability to other foundation pit excavations.

In geological engineering, a series of safety problems caused by expansive mudstone are common, such as slope instability and roadbed up-arch. In this paper, the mineral composition of mudstones in the Xining area was analyzed by X-ray diffraction (XRD), and the microstructural and morphological changes of mudstones after water absorption were observed by scanning electron microscopy (SEM) test to analyze the internal factors and microstructural evolution patterns of water absorption and swelling of mudstones. Based on the microstructural units, the mudstones were defined into two categories, one is N-type mudstone with flat sheet-like stromatolite units, and the other is SN-type mudstone with more clastic particle units. Water absorption experiments were conducted on the rock samples to study the microstructure of these two types of mudstones under different water absorption conditions. The pore characteristics of the mudstones were analyzed by using Image-Pro Plus to reveal the water absorption mechanism. The results show that the pore area of N-type mudstone is smaller, as well as the distribution of pore diameter. The pore area of N-type mudstone develops rapidly, in the early stage of water absorption, lots of pores are produced, and the pore area of SN-type mudstone shows an overall decreasing trend. The pore area and the number of SN-type mudstones are at a low level after full water absorption. Under the condition of full immersion, water enters the pores rapidly and soluble salts are dissolved in large quantities. The change of water absorption rate of mudstone with time can be divided into the stage of sudden increase, decrease and stability of water absorption rate. Then, based on the stress theory, the relationship between the macroscopic expansion process and the microstructure of mudstone was analyzed. Finally, the energy basis of mudstone water absorption is discussed. In the swelling of mudstone, the energy gradually turns into swelling strain energy.

Due to pollutants from industrial and agricultural activities, the lakes in China are faced with ecological and environmental problems. The five most famous lakes of Jiangsu Province, Taihu Lake, Gehu Lake, Gaobaoshaobo Lake, Hongze Lake, and Luoma Lake, have long-term fixed monitoring points for water body-related indicators. Over a five-year period, the monitoring showed that Gehu Lake had the highest average total nitrogen (TN) and total phosphorus (TP) concentrations among all lakes which were close to the Grade V critical value of the China’s Environmental Quality Standards for Surface Water (CEQSW). The NH₃-N concentrations in all lakes were Grade IV according to the China’s Water Quality Standard for Drinking Water Sources (CWQSDWS) and Grade II according to the CEQSW. In addition, although TP concentrations in Taihu Lake did not exceed Grade V in the CEQSW, TP removal was the main factor controlling eutrophication. It was also found that the petroleum concentrations in all lakes were lower than the Grade I according to the CEQSW. Despite this relatively low petroleum pollution, the concentration of petroleum was negatively correlated with the phytoplankton densities in all lakes. This indicated that phytoplankton density was very sensitive to petroleum concentration. For heavy metals, the concentrations of Pb, Cu, As, and Cd in all lakes were significantly lower than Grade I (CEQSW) from 2013 to 2017. However, the accumulated heavy metals in sediments will remain an important pollution source affecting water quality and aquatic products in the future. The comprehensive pollution index analysis showed that the five lakes were often moderately polluted, indicating that the protection of lake resources in China should not be relaxed for a long time in the future.

Carbon emission is one of the main causes of global climate change, thus it is necessary to choose a low-carbon method in the contaminated soil remediation. This paper studies the adsorption ability of ZVI on Pb(II) contaminated soils under different working conditions. The removal efficiency of Pb(II) was 98% because of the suitable ZVI dosage, log reaction time and low initial solution concentration. The whole balancing process was much fast according to the pseudo-second-order kinetic and Freundlich isothermal model. Moreover, sequential extraction procedure (SEP) showed Pb(II) was transformed from Fe/Mn oxides-bound form to residual form in Pb(II) contaminated soils. From scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and X-ray diffraction (XRD) results, it was confirmed that zero-valent iron (ZVI) stabilizes Pb(II) pollutants mostly through the combination of chemical adsorption and physical adsorption. The economic and carbon emission assessments were used to compare the cost and carbon emissions of different methods. The results show that ZVI adsorption has excellent economic benefits and low carbon emission.