Mechanical Behavior Response Analysis Of Nanning Metro Tunnel With Swelling Rock Due To Rainfall Infiltration

Expansive rock and soil is a kind of water sensitive material.Under the action of rainwater infiltration,the rock and soil body undergoes obvious volume change due to the change of humidity.When the deformation is restrained,it generates large internal stress and a force will be exerted on the adjacent structures that constrain the deformation,which will have a negative impact on the stability of shield tunnel and surrounding rock passing through it.It is of great theoretical significance and engineering application value to study the influence of rainfall infiltration on the mechanics and seepage characteristics of expansive rock tunnels and surrounding rock.This paper relies on the section of Nanning Metro Line 1projecting through expansive mudstone.In this paper,the effect of rainwater infiltration on the seepage field and stress field of the expansive rock tunnel and its surrounding rock is analyzed by means of numerical simulation and laboratory model test.The main research work of this paper is as follows:(1)According to the climatic conditions,hydrogeology and engineering environment of the project site,the mechanism analysis of the swelling and shrinkage property and fissure property of the expansive rock is carried out.Samples of expansive rock at the location of the project are taken for laboratory tests to obtain basic physical and mechanical parameters of expansive rock.The variation law of expansive force is obtained by fitting regression,which provides the basis for the subsequent numerical simulation.(2)Based on the basic theory of unsaturated soil and unsaturated seepage,the seepage system of unsaturated soil under rainfall infiltration condition is summarized.The results show that the surface of the ground,the bottom of the fissure and the top of the groundwater level are the main places where rainwater accumulates.At these locations,the matric suction of the soil is reduced so that the shear strength of rock and soil is weakened.The fracture distribution and fracture morphology of the expansive rock mass are factors that affect the stability of the rock and soil.(3)Based on the practical project of expansive mudstone tunnel,the numerical model of unsaturated expansive rock tunnel with different fracture morphology,seepage conditions and rock combination conditions was established by simulating the infiltration process ofunsaturated expansive rock under rainfall conditions with FLAC2 D.And the effects of various factors on the surrounding rock system of rainwater infiltration,tunnel and swelling rock are discussed.The results show that the crack will accelerate rainwater infiltration.The increase of rainfall load and the rise of groundwater level will reduce the bearing capacity of soil and increase the surface settlement.When the rainfall intensity exceeds a certain value,the rainwater will not completely infiltrate.Short time of small rainfall will not significantly affect the soil,the lower water level,and long time of small rainfall will make the tunnel structure has a certain safety risk.(4)The effect of rainwater on the mechanics and seepage characteristics of the tunnel and its surrounding rock is verified by the data of the laboratory test with small scale.The results show that the change of soil moisture content is affected by water source distance,rainfall time,rainfall intensity and groundwater level.In the process of rainfall infiltration,the expansive mudstone exerts significant swelling force on the shield segment,and the shield segments on both sides move towards the tunnel.However,the displacement on both sides of the tunnel piece in non-expansive rock is very small.The greater the moisture content of surrounding rock is,the more significant its acting force on the pipe segment is,and the greater the deformation of the pipe segment is.