Research On Loess Slope Failure Mechanism And Mitigation Technology Under Rainfall Infiltration

Carrying out the research has important theoretical significance and application value on loess slope failure mechanism analysis and prevention techniques by rainfall infiltration. This paper started with rainfall infiltration induced factors and used integrative method of unsaturated seepage mechanics analysis, physical model tests and finite element numerical simulation method to research failure mechanism, to evaluate the stability and to propose mitigation techniques of loess slope by rainfall infiltration under the background of typical Chinese loess slopes.Based on the rainfall characteristics and slope type on the Loess Plateau, the main influential factors were given to damage loess slope under different types of the rainfall and the analysis model was established on loess slope seepage field. A two-dimensional equation of unsaturated seepage was gained by porous media and hydraulics theories. Analytical solution of transient moisture was derived inside loess slope in rainfall. The rainfall infiltration depth and the slope surfaces of saturated thickness were determined.The relationship between ? and moisture content was established according to the approximate relationship between the Bishop effective stress principle of unsaturated soil parameter ?and saturation. The relevant factors were determined in the relationship of the parameter ? and the moisture content with the GDS test system of stress path tests. In accordance with the relationship between parameter ? and moisture content, the relationship of unsaturated loess effective stress and moisture content was established and the unsaturated loess slope effective stress formula was obtained with rainfall varies.Based on the effective stress expression of unsaturated loess, the shear strength formula of unsaturated loess was provided, regarding the rainfall intensity, rainfall duration, initial moisture content and position as the independent variables. Using the simplified Bishop method for analysis of unsaturated loess slope, the safety factor calculation formulas are obtained to evaluate the stability of unsaturated loess slope.The physical experiment research of loess slope failure mechanism was finished under rainfall infiltration. The rainfall data were obtained on rainfall intensity and rainfall duration by model test. The model test loess initial moisture content, transient moisture content, density and dry density were obtained by moisture content and density test. The relationships were fitted between the transient moisture content, infiltration depth up front, saturated thickness, unsaturated loess effective stress and rainfall intensity, rainfall duration, initial water content, location. The relevant parameters were gained. The relational expression was fitted between seepage characteristic parameters and the dry density of loess slop in rainfall infiltration, simplifying the expressions of transient water content and the effective stress obtained by percolation theory and the effective stress principle of unsaturated loess and it is more convenient to use the simplified expression. The result was obtained that both were consistent, verifying the theoretical analysis accuracy.Based on rainfall infiltration of loess slope model, two dimensional flow equation was gotten. The rainfall infiltration seepage equation of finite element analysis of loess slopes was established by Galerkin method. The loess slopes stability were analysised by the strength reduction of rainfall infiltration on loess slope safety factor for the different slope angles, slope height, initial volumetric, water content, rainfall intensity, rainfall duration, dry density. Studies show that: the loess slope safety factor decreased with the slope angle, the slope height increased, reducing the amplitude smaller and smaller, the safety factor fluctuated widely. The loess slope safety factor decreased with the initial water content and the dry density increased, reducing the amplitude bigger and bigger, the safety factor fluctuated somewhat widely. The loess slope safety factor decreased with the rainfall intensity and rainfall duration increased, reducing the amplitude smaller and smaller, the safety factor fluctuated little.Based on loess slope failure mechanism analysis of rainfall infiltration, loess landslides and collapse disaster were putted forward. The preventive measures were putted forward for rainfall-induced loess landslides, such as surface and underground drainage, pile, anchor, anchor the trellis and gravity retaining walls and so on. The preventive measures were given for rainfall-induced loess collapse, such as risk soil anchoring, risk soil support, the risk soil cleared, filling, closing fencing and so on. The structural design calculation expressions were gotten by the rainfall infiltration of loess landslides and collapse prevention measures.The Haizemiao slope engineering being the support, the loess slope of failure mechanism was analyzed by loess landslides criterion under rainfall infiltration. For the loess landslide, the control measures were raised that associated surface drainage, subsurface drainage and anti-slide pile. It was verified that loess slope failure mechanism and mitigation techniques are reasonable under rainfall infiltration. Conclusions have reference value for relevant research.