The dynamic failure mechanism of horizontally layered dangerous rock during earthquakes is complex and only few studies have addressed the combination of particle flow code (PFC) meso-level failure mechanism and mechanical analysis. Based on fracture mechanics and material mechanics we establish a calculation method for the interlayer load and stability coefficient of horizontal layered dangerous rock during strong earthquakes. The method was applied for calculating the stability of a horizontally layered dangerous slope along a highway in the Sichuan Province (China) during earthquakes as a case study. Using a 3D particle flow simulation technology, a PFC3D model of horizontal layered dangerous rock was established. Its dynamic stability, failure mode and Hilbert-Huang 3D time-frequency characteristics are analyzed, and the results of the simulation are largely consistent with the time of the dangerous rock failure as estimated by our new calculation method. Our study documents that as the seismic acceleration gradually increases, the stability coefficient of the rock block fluctuates more violently and the stability coefficient gradually decreases. The stability coefficient of the rock block decreases fastest between 5 and 6 s and the reduction in the stability coefficient is between 0.12 and 0.25. Before the seismic acceleration reaches the maximum, the dangerous rock blocks on the two main controlling structures collapse and get destroyed. 25 s after the earthquake, the failure mode of the dangerous rock is collapse-slip-rotation. We show that earthquakes with frequencies of 0–10 and 250 Hz have the strongest destructive effect on the stability of the horizontally layered dangerous rocks.
Soil pollution in coal mining areas is a serious environmental problem in China and elsewhere. In this study, surface and vertical profile soil samples were collected from a coal mine area in Dazhu, Southwestern China. Microscopic observation, concentrations, chemical speciation, statistical analysis, spatial distribution, and risk assessment were used to assess heavy metal pollution. The results show that the weathering of coal-bearing sandstone and mining activities substantially contributed to soil pollution. The concentrations of Fe, Ni, Cu, Zn, Mn, Cd, Hg, and Pb exceeded their background values. Cd caused the most intense pollution and was associated with heavily–extremely contaminated soils. The residual fraction was dominant for most metals, except Cd and Mn, for which the reducible fraction was dominant (Cd: 55.17%; Mn: 81.16%). Zn, Ni, Cd, and Cu presented similar distribution patterns, and Hg and As also shared similar distribution characteristics. Factor 1 represented anthropogenic and lithologic sources, which were affected by mining activities; Factor 2 represented anthropogenic sources, e.g., fertilizers and traffic pollution; and Factor 3 represented the contribution of metals from soil-forming parent material. More than half of the study area had high pollution risk and was not suitable for vegetable cultivation.
The speci c soil components such as soil organic matter, Fe and Mn oxides exert a signi cant in uence on Cu(II) adsorption in soil. In the present study, clay fraction was separated from an alluvial acid soil, Then the selective chemical extraction method was used to remove the speci c components in the bulk soil and clay fraction. Adsorption experiments showed that the adsorption capacity of the clay fraction of Cu(II) is greater than that of the bulk soil, regardless of whether it is treated by selective chemical extraction or not. Compared with untreated soil samples, after the removal of organic matter by H 2 O 2 , K d decreased by a maximum of 82.8% for the bulk soil and 73.5% for the clay fraction. After the removal of manganese oxides by NH 2 OH•HCl, K d decreased by a maximum of 68.1% for the bulk soil and 73.2% for the clay fraction. However, after the removal of free iron oxides by dithionite-citrate-bicarbonate, K d increased by a maximum of 422% for the bulk soil and 195.5% for the clay fraction. K d increased by 4263.3% when the initial pH increased from 2 to 3.5 and, then, increased to 6. The amount of Cu(II) adsorbed did not change signi cantly. Within a range greater than 6, the increased Cu(II) adsorption may be due to the precipitation of Cu(II). When the concentration of NaNO 3 changes from 0.01 to 0.1 M, the adsorption capacity decreased by a maximum of 36%, K d decreased by a maximum of 84.3%. The presence of foreign ions decreased Cu(II) adsorption; their order of effect on Cu(II) adsorption is Na + < K + < Mg 2+ < Ca 2+ for cations and NO 3 − < SO 4 2− ≈ Cl − for anions. The adsorption of Cu(II) was an endothermic and spontaneous process under the experimental conditions.
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