Study On The Effect Of Surface Water Infiltration On The Dynamic Behavior Of The Loess Tunnel

With the continuous development of China’s infrastructure construction,China has become a veritable tunnel country,whether in the tunnel mileage and quantity,or tunnel design and construction technology has made great progress,but also in the tunnel survey,design and construction has accumulated a lot of experience.At the same time,the tunnel design planning and construction of various problems are also exposed,especially in the treatment of loess and other special soil,how to deal with the wet trap of loess,solve the partial pressure caused by the local wet trap of surrounding rock,stress concentration and other engineering problems,has become the Yellow Land Area tunnel design and construction needs to consider an important issue.In this paper,the theoretical research and numerical simulation are carried out,and the following main results are obtained.(1)The homogeneous loess with different initial water content was simulated under different rainfall conditions,and the seepage simulation under different joint opening degree,different number of joints and impermeable water layer was carried out,and the simulation results showed that homogeneous loess seepage was Intensity and natural moisture content,rainfall,loess saturation penetration capacity are closely related,natural loess with large natural moisture content,vertical pore development seepage coefficient can form a wet area seeping into the formation in a short period of heavy rainfall.The large openness theorem will form the seepage advantage channel when the surface water penetrates,when the opening degree gradually increases,the wet area range will change from semicircle to cone to lead hanging linear seepage field.The increase in the number of joints in a small range can play a better role in water conduction,and produce a larger width of wet front and saturation area,and in the late infiltration of multiple sections than a single section can better import surface water into the depths of the soil,accelerate surface water infiltration.(2)Five different numerical simulations of the surrounding rock immersion and wet subsidence conditions were carried out on the completed tunnel,and the following conclusions were obtained:the surface water is evenly into the seepage condition,the rock layer subsidence is uniform,the lining is mainly affected by the heavy increase of the surface rock layer and produces a certain vertical displacement,displacement and stress growth is not large and uniform.Tunnel-lined arch flooding mainly affects the force of the vault and arch shoulder,which causes the arch and the arch shoulder stress on both sides to increase significantly,and the other positions to be less affected.Under the condition of symmetrical distribution of infiltration areas such as surface uniform infiltration and vault immersion,the horizontal displacement of formation and tunnel surrounding rock and lining is not large,bending moment,axis force symmetry distribution,and the tunnel is not affected by the bias effect.Under the condition of arch shoulder immersion,the arch,arch shoulder and arch waist will have significant stress increase and the imbalance of force on both sides,the horizontal displacement is increased and the horizontal displacement of arch shoulder and arch waist is asymmetric,and the characteristics of tunnel bias force are significant.Tunnel arch foot immersion has the greatest impact on the self-acceptance capacity of the tunnel perimeter rock,and the surrounding rock and lining on the immersion side will produce a large settlement,and the lining bending moment will be significantly improved.(3)Using the three-step method and the center cross diaphragm method(CRD),the tunnel excavation simulation of 4 kinds of surrounding rock immersion is carried out,and the following conclusion is drawn:the CRD method has the advantages of optimizing lining force,effectively controlling lining displacement and surrounding rock settlement under various operating conditions.The CRD method has no obvious advantage over the control of the arch displacement and the three-step method under the condition of vault immersion,but it has good effect on the overall displacement control of lining.Arch shoulder immersion tunnel partial pressure operating conditions,the CRD method excavation can effectively control the settlement of surrounding rock and reduce lining,arch,arch shoulder subsidence than the three-step method reduced by 30%,lining maximum bend moment value decreased by 35%compared to the threestep method.Therefore,under the condition of water immersion of the surrounding rock on the side of the tunnel,it is advisable to use the construction method of closed support for each step of construction to control excavation subsidence and make full use of the surrounding rock self-supporting capacity.