Study On The Influence Of Rainfall On The Deformation Law Of Tunnel Entrance In Jointed Loess

Due to the existence of a large number of vertical joints in the loess layer,the soft structural surface of the loess is formed.After the disturbance of the stratum by construction,these weak structural planes respectively cut the soil into various unstable structures;meanwhile,It is also the channel for water infiltration and the water-giving space,which has certain influence on the stability of tunnels and slopes in the loess area.In this paper,the infiltration law of loess joints and the influence on the Deformation Law of tunnels are studied in depth through on-site investigation,indoor experiments and numerical simulation.In the process of jointed loess model test,the original jointed loess is taken as the research object,and the self-designed natural joint seepage simulation test device is used to obtain the influence rule of joint and its opening and infiltration time on the water infiltration depth of jointed soil: rainfall first penetrates through the joint,and at the same time infiltrates from the joint to both sides,and the water infiltration depth of joint sample is far greater than the average.The greater the joint opening is,the greater the water infiltration depth is.At the same time,the seepage module of Geo-Studio software is used to simulate the model test.According to the comparison between the numerical simulation results and the model test results,the joint equivalent permeability coefficient is obtained,and the cubic law is modified,and then the modified hypercube law is obtained.Based on the model test,the effects of different joint spacing,joint number,slope gradient and rainfall intensity on the water infiltration depth are studied.The results show that the number and spacing of joints have a great influence on the infiltration depth of joints in the process of rainfall.The smaller the spacing of joints,the more the number of joints,the greater the infiltration depth of rainfall.On the basis of model test and Geo-Studio software simulation,this paper uses ANSYS finite element calculation software to simulate the excavation of two-dimensional tunnel portal under the condition of rainfall.By comparing the similarity between ANSYS thermal analysis module and seepage process,parametric programming design is carried out,which is applied to the analysis of water flow and seepage of jointed soil.The effects of rainfall duration,joint number and joint location on the deformation of tunnel portal excavation in jointed loess are studied.Based on the analysis of the changes of stress and displacement at the key points of the tunnel,the deformation law of the tunnel portal and its adverse effect on the surrounding rock during the process of rainfall infiltration are obtained: when there is joint infiltration at the tunnel portal,the vault settlement,relative deformation at the arch waist and relative deformation at the arch foot of the tunnel with joint increase 82.16%,198.65% and 144.5%;respectively compared with the tunnel portal without joint;the section When the tunnel is located at the arch crown,the settlement of the arch crown and the deformation of the invert bottom are greater than that of the joint at the arch waist,in which the settlement of the arch crown at the joint at the arch crown is 1.27 times of the settlement of the arch crown at the joint at the arch waist;the number and spacing of joints have a greater impact on the settlement of the tunnel arch crown,but have a smaller impact on the convergence deformation at the arch waist and the vertical deformation of the invert.