Study On The Interaction Of Shallow And Soft Surrounding Rock And The Supporting Structure Of Phoenix Mountain Tunnel

In the construction of shallow tunnel, force and deformation characteristics of surrounding rock andthe supporting structure are the key to keeping tunnel stable, especially in the soft surrounding rock section.Stability evaluation of surrounding rock and the supporting structure is closely related to tunnel design andconstruction, reasonable parameter selection of the supporting structure is a guarantee of tunnelconstruction and operation safety, so it is necessary to make a study on the interaction of soft surroundingrock and the supporting structure of shallow tunnelRelying on the construction project of Phoenix Mountain Tunnel, through measured data inconstruction field, and combined with finite element numerical simulation, this paper made a study on theforce and deformation characteristics of soft surrounding rock and the supporting structure of shallowtunnel. The main results are as follows:1. Through measured data in the construction field, we obtained that:(1) tunnel surrounding rockpressure distributed uneven, the value in tunnel invert bottom and arch foot is bigger.(2) The initial liningpressure on secondary lining and the secondary lining concrete stress were both small, far smaller than theaxial compressive and tensile press of C25first shotcrete and C30secondary lining reinforced concrete, thetunnel force and deformation were small, and the supporting structure was safe.(3) During tunnelexcavation, with the distance of tunnel face with test section increasing, the tunnel face constructiondisturbance to the surrounding rock in test section gradually reduced, when the distance was greater than15m, the disturbance had been very little, the surrounding rock in test section gradually reached toquadratic stability.(4) The maximum value of surrounding rock cumulative settlement appeared in thetunnel vault, which was separately25mm and30mm in the two test section; the maximum value ofconvergence amount appeared near spring line, which was separately11mm and12mm.2. Trough finite element numerical calculation, we obtained that:(1) when the thickness of tunneloverlying rock varied from5m to20m, tunnel surrounding rock stress increased, surrounding rockdeformation decreased; when the thickness varied from20m to60m, surrounding rock deformationincreased, so it was concluded that the20m of overlying rock thickness is the limit thickness to developarching effect.(2) The bias pressure of tunnel overlying rock led to surrounding rock stress in tunnel rightside bigger than left side, the vertical deformation in tunnel right haunch bigger than tunnel vault, thesurrounding rock vertical deformation of bias pressure tunnel was controlled by the vertical deformation intunnel haunch of bias pressure.(3) During tunnel construction from upper bench cutting to secondary liningclosed, the surrounding rock stress gradually decreased, the surrounding rock deformation and supportingstress gradually increased; when using benching tunneling method, the supporting structure force wasuniform and stable, it could effectively resist surrounding rock stress, and ensure tunnel construction andoperation safety.The study results provided the scientific basis for tunnel design and construction under shallow andsoft surrounding rock, which have an important theory and engineering practical value.