Deformation Mechanism And Prevention Technology Of Shallow Buried Expansive Soil Tunnel In Landslide Area

With the development of infrastructure construction in central and western regions of China,the scale of expressways in mountainous areas is increasing constantly,Many of which pass through special land areas such as expansive soil and landslide areas.When the tunnel entrance pass through these areas,geological hazards often occur in tunnel construction due to the joint action of expansive soil and landslide,which influence the construction process and quality.Therefore,it is very necessary to study the influence of expansive soil and landslide on the deformation of tunnel structure and put forward the corresponding pre vention and control measures.In this paper,the deformation mechanism and control technology of expansive soil tunnel in landslide area are studied based on the project of Sanxi Expressway in Henan Province by means of laboratory test,theoretical analysis,numerical simulation and field monitoring and the main results are as follows:1.The basic mechanical indexes,swelling potential,swelling force and swelling rate of expansive soil are determined by laboratory tests.The physical and mechanical properties,where the volume deformation is considered,of expansive soil surrounding rock are studied.the soil-water characteristic curves which can better estimate the strength,deformation and permeability coefficient of unsaturated soil and reflect the water holding capacity of soil under suction are given.2.the analytical solution of tunnel excavation considering soil swelling characteristics is deduced,and the characteristic curves of weak expansive soil surrounding rock under different water content are obtained according to the theory of elastic-plastic mechanics.The curves can reflect the influence of weak expansive soil surrounding rock swelling on supporting force and deformation.3.the influence of landslide sliding caused by water swelling of tunnel entrance on the stress and deformation of surrounding rock and initial supporting structure of tunnel is analyzed by using finite difference software FLAC 3D,and the deformation and stress of tunnel surrounding rock and initial supporting after tunnel excavation and supporting are analyzed when the longitudinal displacement of landslide body is 3 cm,5 cm,8 cm and 12 cm respectively.The effect of cutting slope unloading on landslide stability and tunnel deformation is studied.The results show that the initial support structure of the tunnel undergoes a large deformation along the longitudinal direction after the water swelling of thesurrounding rock.The maximum longitudinal deformation is 68 mm,located in the middle part of the tunnel vault.With the development of the landslide,the longitudinal deformation gradually extends to the arch waist and arch foot,and the initial support deformation in the landslide increases rapidly.The results of numerical calculation and field construction practice prove that it is not feasible to construct the landslide section at the tunnel entrance without unloading and tunnel reinforcement measures.4.The influence of reserved core soil method,CD method and CRD method on surrounding rock deformation of shallow-buried weak expansive soil tunnel passing through landslide area is analyzed by numerical simulation according to the characteristics of shallow-buried expansive soil tunnel together with field monitoring data.The results show that the deformation of surrounding rock can be well controlled by using CD method in shallow-buried expansive soil tunnel construction.And supporting pressure is a suitable construction method.According to the calculation results,a suit of construction methods for expansive soil tunnel in shallow buried section is summarized,which can provide reference for similar projects.5.It is considered that controlling or reducing the deformation in the excavation process is the key to prevent the failure of the expansive soil tunnel landslide system through the analysis of the development of the crack deformation and the landslide characteristics of the tunnel through the landslide section.Combining with the numerical results and considering the geological environment,construction period and environmental protection in the landslide area,the landslide control measures and the tunnel construction method of shallow buried section are put forward.Through the treatment,the deformation and destruction of landslides have been effectively curbed.At the same time,through the feedback of field construction,it can be seen that the CD excavation method can effectively control the surrounding rock deformation and support pressure.The research results can provide reference for similar projects.