Theoretical Studies On Gravatational Erosion And Sediment Transportiong Capacity

Gully erosion is one of the main forms of soil erosion. Gully erosion amount is often more than 50%-70% of the entire watershed erosion, and gully slope instability can result in backwater in the upstream or floods in the downstream, which poses a huge threat to people's lives and property; Soil erosion prediction model can provide technical support for soil and water conservation and disaster prevention and reduction. However, current soil erosion models are all prediction models based on the slope or watershed scale, and special simulated gully erosion models are rarely. On this basis, in this paper, gully erosion model with the effect of gravity erosion was established, and following results were obtained:1. Calculation formulas and factors of shear strength of sand, clay and structural soil were explained. Given the importance of soil mass structure, it was summarized through microscopic morphology, solid mechanics and soil mechanics approach. On this basis, the concept of structural scale transfer and related methods were firstly proposed and soil constitutive conceptual model based on structural scale transfer was developed.2. The general limit equilibrium calculation method and simplified forms of non-saturated soil were established, and they were extended to the limit equilibrium calculation in saturated soil; Judgment method of the overall soil break based on damage functions and strength criterion was proposed; According to the energy dissipation and energy balance principle, the prediction model of movement distance calculation of landslide was developed. Take the example of the landslide of Loess Plateau border in Dongfeng village, Jingyang County of Shaanxi Province, safety coefficient was calculated with the integral method and the general limit equilibrium method, and the circle center of landslide circle arc, the most dangerous sliding surface, cross-section area were determined.3. According to W.M. Davis'erosion cycle theory and W. Penck'parallel slope recession theory, combined with the characteristics of gully erosion in Loess Plateau, calculation models of slope and down erosion were proposed, which include two types of parallel slope recession and non-parallel slope recession.4. Lumped flow calculation methods consist of reservoir routing calculation of lever reservoir, characteristic river length method, Muskingum method, Muskingum method, nonlinear Muskingum flow routing method and the corresponding river water level (flow)method were summarized. On this basis, the concept of characteristic river length was analyzed and it was extended to any river length, finally new method of determining characteristic river length --drawing method was proposed; On the basis of hydrology and hydraulics principles, through the establishment of reach groove storage equation, the connection bond of characteristic river length, Muskingum method and diffusion wave power equation was found, which can reflect effects of additional gradient ratio on the flow, in view of this, the method to improve the flow calculation accuracy of Muskingum method was proposed; Through the assumption of river hydraulic characteristics, three formulas of flow ratio coefficient X calculation was derived, and the mechanism which X has nothing to do with the entire river length was explored, and the relationship between X and flow factors of calculating step and river bottom slope was obtained, and the Muskingum-Counge flow calculation program was compiled.5. Considering results of water flow calculation and slope stability, equilibrium sediment transport capacity formula and non-equilibrium sediment transport capacity formula of water and sediment calculation were determined.