Study On The Mechanism Of Soil Moisture Responding To Rainfall And Its Redistribution In Collapsing Hill

Granite collapsing hill was the most seriously soil erosion in southern China.Soil moisture is the power and premise of collapsing hill.Field survey and monitoring and using hyetometer and soil moisture monitoring system were used.This article analyzed the soil layers' response mechanism to rainfall and its profile water characteristic.And soil samples were collected intensively from different soil layers in vertical soil profile,which was used to analyses the permeate and influence factors of different soil layers.The main conclusions were as follows:(1)The water content of different soil layers were influenced by rainfall amount and its duration and its intensity.Continuous rainfall had a bigger influence on water content than that of sec-rainfall;red soil layers responded more sensitively to rainfall than other two layers.There had hysteresis effect in this progress,especially in the big rainfall intensity.(2)the permeate of vertical soil profile in collapse hill had a great difference.Red soil layer had a stronger permeability than other two layers.Under the 0.1m soil layer,there were relative impermeable layers and its thickness was about 1m.Stepwise regression was used to analyzed influence factors on permeate of different soil layers:the main factors were volume-weight and fractal dimension for relative impermeable layers,which was clay content for sandy soil layers,and fractal dimension for debris layers.(3)Collapse hill was mainly made up of larger particles(>0.05mm).Different soil layers had different fractal dimension,the red soil layer was mainly made up of silt content,which were silt and gravel for sandy soil layer,and was gravel for debris layer;From the results of fractal dimension analysis for different soil layers,we can conclude:D(red soil layer)>D(sandy soil layer)>D(debris layer),fractal dimension and silt content was significantly positively related with fractal dimension through the stepwise regression.(4)Collapsed hill had a poor water-holding capacity.The wariation rang of red soil water content was small at 40 cm and 60 cm layer on vertical soil profile.The three layers' water-holding capacity receded gradually as depth increase on horizontal direction.Red soil layer had a better water-holding capacity than other two layers,and debris layers hardly impound at 20cm.Comparing the water characteristic curve of sandy soil layer and debris layer:under same suction,sandy soil layers' had a higher water content than that of debris layer.