Influenced by the topography, the spatial variation of soil thickness on karst slopes is very large, and accordingly the spatial variation of soil moisture is also large. Therefore, analyzing the spatial heterogeneity of soil moisture on hillslopes is important for maintaining ecosystem stability. Combining geostatistical methods and GIS technology, the spatial variability and distribution pattern of soil moisture and the influencing factors of spatial variation and surface soil moisture (0–7 cm) on a typical karst shrub–grass hillslope were analyzed. The results showed that the mean soil moisture and coefficient of variation (CV) ranged between 25.7–42.6% and 10.3–20.9%, respectively, showing a moderate variation. The soil moisture presented a moderate or strong spatial autocorrelation in the sampling scale. The occurrence of rainfall events can exert a great influence on reducing the spatial heterogeneity of soil moisture. The spatial distribution pattern of soil moisture showed roughly plaque or stripe distribution. When soil moisture was much lower, the patch space fragmentation of soil moisture was higher. The soil moisture was higher in the low and middle parts of the plot. We can conclude that factors such as topography, vegetation, and weather conditions will exert a significant effect on soil moisture spatial variability. Areas with lower slope and higher vegetation coverage were more conducive to the retention of soil moisture.
Abstract. Based on the case Nanjing Metro Line 4, the method Principal Component Analysis (PCA) was used to study the influence of ground settlement by shield tunnel construction on different geomorphology units. Correlation analysis and weighted least square method (WLS) were applied for variables selection and to obtain their relationship with settlement. 5-7 principal components could be used to present the initial 19-21 variables after decreasing the dimensions of data. For the floodplain of Yangtze River, variable parameters that highly linearly dependent on settlement were depth of tunnel, distance between the roof of tunnel and the bottom of soft soil layer, thickness of soft soil, compression modulus of soil that tunnel passed through and speed of the cutter head. For the Qinhuai ancient channel, variable parameters were Poisson's ratio, porosities, moisture content, unit weight, cohesion, internal friction angle, compression modulus of soil that tunnel passed through, advancing speed, earth chamber pressure. For the terrace of Yangtze River, variable parameters were cohesion, porosities, moisture content, Poisson's ratio, compression modulus and unit weight of soil. In addition, for the geomorphology unit with col landform, variable parameters were different. Residuals of regression formula are small, which will have certain reference value in practical engineering.
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