Study On Influence Of Rainfall Infiltration On Soil Arching Effect And Earth Pressure Between Piles

Rainfall in the rainy season is frequent in parts of southwestern China.Rainfall is easy to induce geological environmental disasters and secondary disasters,which pose a huge threat to people’s production and life.Especially in the western mountainous areas such as Sichuan,Chongqing,Tibet and Yunnan,major geological disasters such as landslides,collapses,and mudslides often occur after the rainfall,causing huge economic losses.In engineering construction,anti-slide piles are often used in landslide control projects,but engineering accidents such as soil arch failure and slope instability also occurred from time to time due to rainfall,which poses challenges for construction activities in areas with rich rain-fall.The theory of soil arching effect between piles optimizes the design method of anti-slide piles,but how to consider the influence of rainfall infiltration on the soil arching effect between piles and the theory of earth pressure related to rainfall activities,and many problems are still remained to be solved.Through theoretical analysis,numerical simulation analysis and lab model test,this paper studies the spatial effect of soil arch between piles and the earth pressure of pile-slabs under rainfall conditions.The main work of this thesis is as follows:(1)Based on the analysis of rainfall infiltration process,the influence of rainfall on soil arching effect and earth pressure is mainly due to the decrease of shear strength of soil between piles,the increase of soil weight and the increase of positive pore water pressure in soil.The lab direct shear test of unsaturated sand with different volumetric water content is carried out to obtain the shear strength parameters and soil.The relationship between the change of body volume and water content is conducted,which provide a reference for the calculation parameters used in the derivation formula.(2)Based on the three-hinge arch model,the reasonable arch axis equation of anti-slide piles under rainfall conditions is derived.Based on the static equilibrium conditions between adjacent arches,the relationship between soil arch thickness and the clearance between piles is derived.Depending on the relationship,the distance between the piles is calculated under the control conditions,such as the strength of the arch section,the strength of the leading edge of the arch,and the flow resistance of the pile.Founded on the principle of effective stress,the force balance equation of the micro-element is established.The calculation formula of earth pressure between piles under the condition of rainfall is considered,and the distribution law of earth pressure before and after rainfall is compared and analyzed by numerical examples.(3)The finite element analysis model was established by using ABAQUS numerical simulation software.The stress and strain distribution of the soil between the piles under rainfall was obtained.By comparing and analyzing the stress-strain relationship of the soil at the central axis position on different horizontal slices and the relationship between the stress increments in the soil before and after rainfall,the spatial effect of the soil arch between the piles after rainfall is studied.Based on the variation of pile spacing,rainfall intensity and baffle stiffness,the distribution law of the pile and board pressure under different working conditions is obtained.Combined with earth pressure increment,the variation characteristics of pile and baffle pressure under different working conditions before and after rainfall are analyzed,and the influence law of rainfall infiltration on the earth pressure distribution of pile and baffle is obtained.The numerical simulation results are compared with the theoretical calculation values of earth pressure distribution.The variation law of soil arching effect before and after rainfall under different working conditions is analyzed by calculating the earth pressure sharing ratio of piles.(4)Based on the comprehensive geological environment simulation test system and the self-made test model,ten groups of lab model test of soil arching effect between piles under different conditions of rainfall conditions is carried out,considering pile spacing,rainfall intensity and baffle type as the control variables.By analyzing the phenomenon of soil arch failure between piles,the factors that affect the stability of soil arch between piles are studied.The impact of rainfall infiltration on the incremental pressure distribution of pile and baffle is further verified by analyzing the increment of measured earth pressure on piles and boards.Through the measurement of the volumetric water content of the soil at different positions on the slope during the rainfall process,the variation law of the volumetric water content of the slope under rainfall conditions is obtained.In addition,the measured pore water pressure is verified with the earth pressure on the board caused by the water pressure in the theoretical calculation formula.Through theoretical analysis,numerical simulation and lab model test,the soil arching effect and earth pressure change law between piles under rainfall are obtained.The results can provide a theoretical reference for the design of slope anti-slide piles in areas which are of rich rainfall.