Analysis Of The Influence Of Surface Water Infiltration On The Stability Of Shallow Buried Large Section Loess Tunnel

In the Loess covered area,loess on the surface is generally Q4 and Q3 new loess.The cohesive property of the soil fabric grains is poor and the porosity is large.After the infiltration of surface water such as rainfall or irrigation,the soil structure is easy to be damaged.During the construction period and the tunnel is under shallow buried section,such projects are more likely to generate cracks and pits.The worst possibility is causing landslides,such damage would strongly threat the safety of stuff.Based on a shallow buried large section loess tunnel,using three axis test and field measurement data,analyzed the stability of the tunnel under different rainfall intensity and duration situation by Midas software,the main results are as follows:(1)Retrieved undisturbed soil from a loess tunnel in Guanzhong District of Shaanxi.Tested The natural and saturated moisture content state of the soil.The samples were grouped according to the moisture content,and the three axis shear test and the isobaric test were made.The main conclusions are as follows: with the increase of water content,samples' s elastic and yield stage remained the same,but appeared bvious failure stage;the appearance of the tested samples is affected by moisture content and confining pressure,the damage increased with increasing of moisture content but decreased with the increasing of confining pressure;Elastic modulus and cohesion was influenced by water content seriously,but internal friction angle was affected lightly.(2)Established elasto-plastic constitutive relation of surface water infiltrated loess based on three axis test date,using the Hooke and Drucker theory.Stress strain curve calculated by the constitutive relation is well fitted with the experimental data.Compared with the classic Cambridge model,the new constitutive relation is better applicable to the unsaturated loess in Guanzhong area of Shaanxi.(3)Analyzed the water content of surrounding rock affected by rainfall infiltration by Midas software.Added different volume of surface water According to the rainfall intensity in Guanzhong area is,The results show that water content affected by different rainfall intensity are likely.Moisture content of surface soil reaches saturation after rainfall,influence decrea ses with the increase of depth and the effect can be ignored on the soil deeper than 3 to 5m.Modify the parameters according to the moisture content and use this method to approximate the influence of rainfall on the surrounding rock.(4)The results of the numerical simulation shows that the deformation of surrounding rock was affected by rainfall seriously,sedimentation value increased 20%~40%,stress of support system also increased about 15%~20%.The results sll illustrate that the stability of shallow buried large section loess tunnel is effected seriously by rainfall.The strength of the supporting structure should be strengthened to ensure the safety and stability of the structure.