Yunnan The Lateritic Landslide Indoor Test Studies

On the basis of the comprehensive analysis of the slope stability,the landslide test and the rainfall-induced landslide from home and abroad,the substantial problems of the landslide research are defined.Combining with the characteristics of a large number of the laterite-type slopes existed and rainfall concentration in Yunnan province,the research subject,which is named as "laboratory test research on laterite-type landslide in Yunnan province",is presented.Aiming to the typical laterite in Yunnan province,laboratory landslide tests were carried out with contents such as manufacture of laboratory landslide test apparatus,calibration of rainfall capacity,development of landslide test,research of physical characteristics and shear strength characteristic of laterite and analysis of rainfall-induced landslides mechanism.The acquisitive research-fruits are of great theory and realization significance for the sliding mechanism and prevention of laterite-type landslides.The laboratory landslide test apparatus mainly includes rainfall system,model slot and water collecter.Rainfall characteristics of rainfall system can be confirmed by the rainfall capacity calibration tests.There are practical measurement method and energy modification method to confirm the rainfall of rainfall system.Under the condition that the tap is keeping certain opening,the relationships of both laboratory rainfall capacity and actual rainfall capacity to the tap closed-timing are linear, but actual rainfall capacity is larger than laboratory rainfall capacity, and there is an energy fold reduction factor between them.After finishing the manufacture of landslide test apparatus,aiming to the typical laterite in Yunnan province,under different conditions such as angle of slope,height of slope,moisture content,dry density and molding method including layered-bumping method in horizontal direction, layered-bumping method in vertical direction and packing method,a series of landslide tests were carried out while rainfall grade is rainstorm.The rate of success for laterite-type slope is very low.The occurrence conditions of landslide were as follows:laterite-type landslides are made by packing method,the dry density is smaller,the moisture content and heights of slope are higher.the roof length of slope is longer.and the angle of slope is larger.The sliding surface of the laterite-type landslide is approximate arc shape. when laterite-type slope is sliding.sliding characteristics,such as crack,sliding surface,sliding zone.sliding position,height of slippery wall.sliding lasted-time, sliding way and sign before sliding,can be observated.Whether laterite-type slope is sliding or not,there are several typical phenomenons during rainfall,which include"splash erosion","crust",particles migration and slope destruction.Physical characteristics of the landslide laterite include containing water, density and grain composition.Whether laterite-type slope is sliding or not, with the decrease of the slope height, whose moisture content is growing and density is reducing gradually, whose silt content is increased and clay content is reduced by different degrees.Under the condition of the same position for slope height, moisture content of slide-zone soils is maximum,moisture content of slide-part soils is next,moisture content of slide-bed soils is minimum.The variation mechanism of physical properties is the consequence of a combination of strike action,infiltration action and runoff action on slope surface caused by rainfall.Shear strength characteristic of the laterite which was prepared in different moisture contents and densities, was determined by direct shear tests.With the increase of the moisture content, shear strength and friction angle are reduced gradually in the same dry density, but there is an maxima for cohesion.In the same moisture content, as dry density reduced, shearing strength and cohesion are decreased gradually, but friction angle trends towands enlarger. The variation mechanism of shear strength characteristic depends on the size of the laterite particles, the link between laterite particles, soil structure by the way of arranging among particles and soil suction.In rainfall process, typical phenomenons, such as "splash erosion", "crust", particles migration and slope destruction, can be explained from strike action, infiltration action, runoff action and pore water pressure action on slope surface. Under the action of rainfall, laterite-type landslide mechanism is clarified with weight increase action, soften action and lubrication action.