Influence of Soft Plastic Loess Layer on Surrounding Rock Deformation of Super-large Section Tunnel in Shallow-buried Loess
To solve the problems existing in the construction of Luochuan Tunnel on Xi'an-Yan'an HSR under construction with long distance passing through soft plastic loess layer,this paper numerically simulates and analyzes the surrounding rock deformation,and establishesa construction model by three-bench method with core soil reserved.When the soft plastic loess layer is distributed on arch crown,side wall and arch bottom,different layer thicknesses(1,3and 5 m)have an impact on arch crown settlement and horizontal convergence deformation.This paper puts forward reasonable deformation control measures based on monitoring and measurement data.The study results show that:a)By comparing the displacement of surrounding rock under different distribution and thickness conditions of soft plastic loess layer,it is found that the soft plastic loess layer increases the displacement of surrounding rock,and the distribution of soft plastic loess layer has a more significant impact than its thickness.When the soft plastic loess layer is located above the tunnel arch crown with a thickness of 5in,the impact is the greatest.b)Under the action of advanced pipe shed,the vertical displacement and horizontal displacement of surrounding rock in the shallow-buried soft plastic loess tunnel are reduced compared with those without advanced pipe shed support.Therefore,protection measures shall be taken in time during construction through soft plastic loess layer.c)Arch crown settlement and horizontal convergence around the tunnel display three stages:cliff-like sharp deformation,continuous slow deformation and deformation tending to be stable along with excavation.Therefore,during actual construction,the deformation control of sharp deformation stage in the early stage of excavation shall be carried out in time,and the monitoring and measurement of surrounding rock shall be strengthened.
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