Influence factors of morphological development of soil cracks in degraded slopes in Yuanmou dry-hot valley region

Abstract: Soil cracking is an important process and feature of the slope degradation in Yuanmou Dry-hot Valley Region, which influences water evaporation, solutes transport and soil structure. In this paper, 25 soil crack quads were investigated by using the photography method to describe the morphology of soil cracks, and meanwhile, soil samples were also obtained at soil depth 0-30 cm and >30-60 cm in the same quad. The crack area density (Dc) was obtained by ArcGIS 9.0. The values for soil physico-chemical properties were also obtained by laboratory analysis. And then, the influences of soil physico-chemical properties on the development degrees of soil cracks were analyzed by application of statistical analysis methods. The Results indicate that: (1) The development degrees of soil cracks have a positive correlation with clay content, swell-shrink property and bulk density, and are negatively correlated to organic content and soil porosity. Dc, which is the quantitative indicator for the development degrees of soil cracks has been found to have a significant strong correlation with clay content, their coefficients were 0.97 and 0.95 for 0-30 cm layer and for >30-60 cm layer respectively. And for Dc and bulk density, their relationship also appears significant positively correlated, witch was 0.81 and 0.68 for 0-30 cm and >30-60 cm layer respectively. Dc and swell-shrink property has the same correlation with its coefficient of 0.81. However, as for Dc and organic content, Dc and soil porosity, the correlations were found to be negatively correlated with coefficients of -0.55 and -0.72 for the layer of 0-30 cm. On the basis of that, each regression equation for Dc and other influential factors are given by application of the regression analysis. (2) The soil structural indices (including bulk density, soil porosity and clay content) are the most important factors affecting the development degrees of soil cracks, then followed with swell-shrink property and organic content. Principal component analysis shows that among the 9 principle components, the principle component 1 (PC1), principle component 2 (PC2) and principle component 3 (PC3) are able to explain most of the variance information with their accumulative contribution of 94.98%. And PC1 is the structural factor mainly consists of soil bulk density, soil clay content and soil porosity. PC2 and PC3 mainly reflect soil organic matter and soil swell-shrinkage property. The research results can be expected to provide theoretical references for the further study on soil cracking mechanism and for proposing reasonable measurements on amelioration of cracked soil.