Experimental Study On Improving Slope Stability With PVA And MgO Under Rainfall Conditions

Southeast Tibet is a heavily affected area with frequent geological disasters in China.Its sandy gravel soil and sandy gravel landslides have the characteristics of large scale,difficult prediction,and great harm,becoming an important influencing factor impeding economic and social development in the Qinghai-Tibet Plateau region.Rainfall infiltration,especially continuous rainstorm,is the main factor inducing slope instability,which poses a serious threat to people’s lives and property.Therefore,the study of slope instability has great theoretical and practical engineering significance.In this paper,a slope in Langxian County,Tibet Autonomous Region,was taken as the research object.Rainfall tests were conducted on a sandy soil model slope modified with different improved materials through large-scale physical model tests,and the deformation process of the slope under rainfall conditions was simulated using particle flow software.The test results can provide strong support for the stability study of sandy slope under rainfall infiltration,and provide valuable reference for related projects.The main research contents include:(1)Through field sampling,indoor screening tests,direct shear tests,and permeability tests,the natural density,particle size distribution,shear strength parameters,and permeability coefficients of different types of improved sand at different water content were determined.(2)Three groups of different rainfall intensities and four types of surface soil materials were designed for the test,and the reinforcement effects of different improved materials were compared and analyzed.When the rainfall intensity was 60 mm/h,a landslide occurred on the shallow surface of the slope with the maximum depth of the landslide impact area being less than 20 cm.Magnesium oxide(Mg O)improves the shallow surface of the slope: When the rainfall intensity is 60mm/h,the slope is stable,and when the rainfall intensity is increased to 120mm/h,multiple landslides occur on the shallow surface of the slope,and the maximum depth of the landslide impact area exceeds 30 cm.Polyvinyl alcohol(PVA)improves the shallow surface of the slope: When the rainfall intensity is 60 or 120 mm/h,only small cracks appear on the slope,which is generally stable.When the rainfall intensity increases to 180mm/h,small-scale landslides occur along tensile cracks at the slope toe,and multiple smallscale landslides occur in the front and middle of the slope subsequently.However,the maximum depth of the landslide impact area does not exceed30 cm.PVA+Mg O improved shallow surface of slope: When the rainfall intensity is 60,120,and 180 mm/h,only small cracks appear on the slope,which is generally stable.(3)Each modified material has a corresponding maximum rain resistance.When the rainfall intensity is less than 60mm/h,using Mg O to improve the shallow surface of the slope can maintain the stability of the slope;When the rain intensity reaches 120mm/h,it is necessary to use PVA materials for shallow surface improvement of the slope to maintain stability of the slope;When the rainfall intensity reaches 180mm/h,only PVA+Mg O can be used to improve the shallow surface of the slope to keep the slope from being affected by rainfall and causing landslides.(4)Based on the experiments,the deformation process of slope under rainfall conditions was simulated using particle flow software.The experimental content not carried out in the indoor model was supplemented by numerical simulation tests.Based on the PFC-FLAC coupling method,a slope model with the same size as the actual rainfall test was established to simulate the deformation process of four types of slope under three rainfall intensities.Macroscopic analysis of slope soil movement in terms of displacement and stress,and mesoscopic analysis of slope soil movement in terms of porosity and crack extension.By observing the particle motion characteristics,the deformation micromechanism of slope after rainfall infiltration is analyzed,providing valuable reference for relevant engineering design and prevention measures.