Stability Analysis Of Slope Of Pinus Massoniana Forest In Huaying Mountain Of Eastern Sichuan

Vegetation can play a certain role in prevention and control of shallow surface landslides through the mechanical action of roots.The shallow landslide occurred on Pinus massoniana forests in Huaying Mountain.But these landslides have some different what the shallow landslide only occurred on both sides of the slope and lead to the bedrock to be exposed.The middle part of the slope has not been affected.There is still a complete Pinus massoniana forest.In order to explain the reasons for this phenomenon,through field investigation,indoor geotechnical test,Hydrus software simulation of soil water movement and slope stability analysis under different factors,the root reinforcement effect of steep slope forest and the influence of soil suction stress were studied.Considering the effects of root mechanical action and soil suction on slope stability.Results show as follows:(1)The number and diameter of roots decrease with the increasing of soil depth.The root cross-sectional area is smaller in the deep soil which with less diameter and root coefficient.Root system can increase the shear strength of soil,and the maximum value of soil shear strength occured in shallow soil with more fine roots.Therefore,fine roots play an important role in enhancing soil shear strength.(2)During the rainfall process,the two groups of landslide are neither reach saturated water content nor produce positive pore water pressure.It is a slope instability that occurs under unsaturated conditions.The suction stress promotes the slope stability in unsaturated conditions.(3)The stability analysis include four cases:there are neither additional cohesive force of the root system nor the soil suction stress,only the additional cohesive force of the vegetation roots,only the suction stress effect and both considering.The analysis results are as follows:1)When the root cohesive force and the soil suction stress are not considered,the slope stability coefficient is less than 1,which is an unstable slope;2)When considering the additional cohesive force of the vegetation roots,the stability coefficient is greater than 1,and the slope safety factor of the root enhancement is 58.82%?107.25%;3)When only the suction stress is considered,the soil suction stress decrease as the water content increases.Thereby reducing the contribution to slope stability.The safety factor of the increase of suction stress during rainfall is not exceed 27.54%;4)When the effects of two factors are both considered,the safety factor of landslide 1 and landslide 2 is less than 1.30.The minimum safety factor of the reinforced soil slope specified in the project is less than 1.30,so the slope is considered unstable.The stability coefficient of the control group is above 1.30,the slope is considered stable.The landslides of this study occurred under unsaturated conditions,and the soil hydrological action played a positive role in stabilizing the slope.However,in the case of heavy rain or extreme rain,the water content increases rapidly to the saturated water content,the suction stress tends to 0 or a positive value.At this time,the additional cohesion of the root is the main factor determining the stability of the slope.This study analyzes the slope stability of Huaying in September 2014 under severe rainstorm conditions,which can provide reference for slope stability analysis under the influence of extreme weather.