Study The Wetting And Drying Cycle On Macropore Characteristics Of Granite Collapse Mound

Collapse mound is a kind of special soil water erosion phenomenon occurred in the southern granite red soil region of china,which is taken place by an interaction of water power and gravity.It’s the one of the most important cause of deterioration of ecological environment.In this experiment one activity type collapse mounds was selected in Tongcheng county, Hubei province with field investigation and laboratory experiments. To study the influence of soil properties and water wetting and drying cycles on the large pore volume and saturated hydraulic conductivity of soil in different soil mass.The main conclusions are as follows:The basic rock and soil characteristics differ greatly between each layer of the soil in the granite collapse.From the surface down vertically, the granite collapse profile is divided into the surface layer, the red soil layer, the sand layer and the debris layer.Comparing the variation law of soil bulk density in each soil layer,the result is the debris layer > the surface layer > the red soil layer > the sand layer; For the mechanical composition of soil, the proportion of sand content is increasing from top to bottom, the sand content of debris layer is highest(66.21%), Compared with the other three layers, which is 1.8 times than the surface layer, 1.73 times than the red soil layer and 1.19 times as much as the sand layer, and the red soil layer > the surface layer > the surface layer > the debris layer. The soil organic matter content in the whole profile are less, and it is less and less from the surface layer to the debris layer.The soil organic matter content in the whole profile are less, and it is less and less from the surface layer to the debris layer. The topsoil organic content is only 19.25g/kg, the content of organic matter in debris layer is the lowest 4.48g/kg. PH value of the surface layer is less than that of the sand layer, the soil layer is weak acidity;Two kinds of soil saturated hydraulic conductivity were different after the whole dry wet cycling of the same number of the two kinds of soil, which were the reconstituted soil and undisturbed soil.1、The saturated hydraulic conductivity of undisturbed soil and reconstituted soil under the action of dry and wet cycle of the same frequency and different frequency was increased,.The undisturbed soil had the maximum value after fifth times, and the reconstituted soil reached the maximum after seventh times..Minimum values occur in the first all wet and dry cycle,and the saturated hydraulic conductivity of the soil between the two kinds of soil is very small, and the saturated hydraulic conductivity of reconstituted soil and undisturbed soil respectively were that the topsoil is 0.21mm/min and 0.20mm/min, the clay layer is 0.65mm/min and 0.65mm/min, the sand layer is 0.75mm/min and 0.75mm/min,and the debris layer is 0.11mm/min and 0.10mm/min. Comparison of two kinds of soil change degree,the change of the saturated hydraulic conductivity of undisturbed soil under the action of wetting and drying cycles is more than reconstituted soil.2、he same kind of soil was under the action of dry and wet cycle in different frequency and times,are all wet and dry cycle constant is greater than half dry wet cycle。The change range of saturated hydraulic conductivity was compared with different frequency。The whole wet dry cycle is more obvious before the fifth action,after the fifth time, the semi dry and wet circulation is more obvious。The number of wet and dry cycles can change the shape characteristics of large pores. The shape of soil pore is approximately circular or elliptical. But also there are irregular shape of the pores and with the increase of the number of wet and dry cycles of irregular large pores more. After the third dry and wet cycle, a large white part of the white part of which appeared a lot of black soil material. With the increase of the number of cycles, the soil pore perimeter showed a trend of increasing first and then decreasing. The overall change is not large, the maximum value is 23.816, the minimum value is 19.633. After wetting and drying cycle, the pore of pore size less than 0.1mm is rapidly decreasing,the increase of soil porosity of 0.2-0.6mm was more obvious, and this treatment had almost no effect on the pore of larger than 0.6mm.