A Stability Analysis Method Considering Stagnant Water Effect Of Subgrade Slope With Soil And Rock Mixture

Soil-rock mixture has unique physical and mechanical properties,and the permeability of subgrade slope formed by SRM is different under the process of rainfall.Therefore,the migration process of stagnant water in the vadose zone of the slope appears hysteresis,that is stagnant water effect.In addition to the geometric characteristics,material properties and rainfall boundary of the soil rock mixture subgrade slope,the stagnant water effect will also affect the stability of the slope.If this effect was ignored,the reliability of slope stability analysis will be reduced.This paper is devoted to studying the stagnant water effect of soil rock mixture subgrade slope and its influence on slope stability,the effect was caused by rainfall.Based on the methods of field investigation,theoretical analysis,laboratory and field tests,numerical simulation and calculation,the evolution law of stagnant water effect under the process of rainfall is emphatically studied,the influence of different factors on slope stability is analyzed,and the stability analysis method of subgrade slope considering stagnant water effect is summarized and proposed.The main research results are as follows:(1)The basic characteristics of the soil-rock mixture were revealed,and the typical failure forms of the subgrade slope of the soil-rock mixture were clarified.The natural mass moisture content of the selected samples is 11%～18%,and the average moisture content is 14.4%.The dry density,saturated density,and saturated moisture content is all positively related to the rock content in the natural accumulation state.The failure form of subgrade slope is mainly inclined layer or bedding landslide of soil-rock mixture accumulation layer.The development stage of landslide coincides with the rainfall period,but the landslide time lags the end of rainfall.(2)The soil-water characteristics and saturated-unsaturated permeability characteristics of the soil-rock mixture were revealed.The soil-water characteristic curves of soil-rock mixture in the process of dewetting and moisture absorption were generated by fitting.There are some differences in the dewetting and moisture absorption curves of soil-rock mixtures with different rock contents,which are negatively related to the rock content and positively related to the nonuniformity coefficient.The saturated permeability coefficient of soil-rock mixture with different rock content was measured,and the unsaturated permeability coefficient of soil-rock mixture was deduced.The soil-water characteristic prediction model and unsaturated permeability coefficient prediction model of soil-rock mixture were established.(3)The phenomenon of"stress fluctuation"and the variation law of saturated-unsaturated shear strength of soil-rock mixture were revealed.The shear strength of soil-rock mixture is positively correlated with the rock content and vertical pressure.With the increase of saturation,the shear strength has a peak in the test range.Based on the improved single stress state variable theory,the saturated-unsaturated shear strength prediction model of soil-rock mixture was constructed.(4)A double index system of stagnanted water quantity Q_h and water stagnant time C_h was established to characterize the stagnant water effect.The evolution process of the stagnant water effect of the subgrade slope of the soil-rock mixture was revealed,and discussing the influence law of different factors on the stagnant water effect.The amount of stagnant water is positively related to the permeability of the material and rainfall.The stagnant time is positively related to the amount of stagnant water and the hysteresis effect(water holding capacity)of the material.The range and extent of the affected by rainfall are positively related to the rock content,rainfall intensity and rainfall duration.The variation law of pore water pressure on the surface of slope is like that of saturation,while hydrostatic pressure appears inside the slope.There is a large fluctuation in pore water pressure at the saturated-unsaturated interface and the interface of strata with different rock content.(5)The stability analysis method of soil-rock mixture subgrade slope considering stagnant water effect was proposed.The relationship between the characteristics of soil-rock mixture subgrade slope and its stagnant water effect is clarified.The stagnant water amount is positively related to the permeability coefficient,effective infiltration area,rainfall intensity and rainfall duration.The influence of stagnant water effect on the spatial characteristics of soil-rock mixture subgrade slope instability was clarified.In homogeneous stratum slope,the stagnant water effect mainly shows the retardation of the sliding surface change process.In the heterogeneous stratum slope,the stagnant water effect makes the stratum with specific particle composition play a blocking role.The influence of stagnant water effect on the time characteristics of soil-rock mixture subgrade slope instability was clarified.The risk lag time D_R is proposed to characterize and analyze the law of the risk lag phenomenon of soil-rock mixture subgrade slope during different types of rainfall.