Research On Law Of Runoff Yield And Soil Mechanical Behavior Of Forestland Slopes In Jinyun Mountain In Chongqing City

The research on law of runoff yield and erodibility of slopes in Jinyun Mountain in Chongqing City was conducted, which are associated with the National Natural Science Foundation of China"Relationship of soil structure and soil erosion in forest lands based on fractal theory in Three Gorges Reservoir Areas". The purpose of this paper is to provide evidence for vegetation construction, exploitation and utilization of sloping land and development of forestry and agriculture.On slope scale, hydrological effects of canopy, litters and soil layers under typical forest vegetations (mixed forest, broadleaved forest, bamboo forest, and shrub) in Chongqing Jinyun Mountain were analysized quantitatively. Slope runoff characteristics of typical forest vegetaions were analysized from data of runoff and rainfall on the scale of month, year: Linear regression relation was found between rainfall outside of stands and rainfall inside of stands; It was observed that absorption rate of litter was very fast and water-holding content increased rapidly within 2 hours; Water-holding content of (semi-) decomposition litters which belonged to shrub, broadleaved forest and mixed forest is 2.5, 2.0 or 2.6 times the amount of that of without deposition litters. The average absorption rate of (semi-) decomposition litters is times (from 2.4 to 4.0) the amount of that of without deposition litters respectively. Hydrological effect about (semi-) decomposition was showed from that. In addition, the most value of retaining water capacity was 282.8mm, which belonged to soil layer of shrub, and mixed forest >broadleaved forest >farmland in sequence; Grey correlation analysis on factors influencing hydrological effects was conducted, and the importance sequence of factors is the content and storage of litter> the (semi-) decomposed litter storage>canopy closure extent>soil porosity>herb coverage> soil holding water capacity; Then hydrological hierarchy function sequence was evaluated using grey correlation analysis as follows: shrub>broadleaved forest>mixed forest>bamboo.The basic parameters of soil hydraulic properties were measured in lab and forest hydrology data were observed in the wild, the unsaturated permeability coefficient of the three soil layers of broadleaved forest were calculated. Leaking field was established from that in order to confirm spillpoint, seepage path and seepage quantity (1.892582m3/d) using node or element contour figure. Spillpoint would rise or fall in accordance with angle of slope, so did seepage quantity. It is useful to protect angle of slope.Unsaturated shear strength was stimulated in the finite element analysis method through total stress and effective stress theory, Drucker-Prager yield criterion was more suitable for describing types of soil failure, which provided the theoretical basis for predicting failure location of soil slope. Stress field was established based on unsaturated shear strength predicted using shear strength of saturated soils and parameters of soil and water characteristic curve, and safety factors of broadleaved forest was obtained as 2.4. From analysis methods concerned about hydrological effect assessment, stress field and leaking field, we could provide scientific basis for vegetation construction, exploitation and utilization of sloping land and development of forestry and agriculture.