Study On The Influencing Factors Of Large Deformation Of Inverted Arch Uplift Of Soft Surrounding Rock Tunnel

The inverted arch structure can improve the bearing capacity and stability of the whole support system of the tunnel,and plays an important role in ensuring the smooth excavation and safe operation of the tunnel.Soft rock has the characteristics of low strength,easy to soften and poor self stability,so the invert structure in high ground stress soft rock tunnel is prone to uplift deformation.It is of great significance to study the causes of invert uplift deformation of soft rock tunnel under high ground stress for guiding the design and construction of tunnel under similar conditions.Based on a tunnel project of Lincang Expressway in Yunnan Province,this paper adopts the methods of field geological survey,field monitoring measurement and numerical simulation to explore the causes of invert uplift deformation of the tunnel in high geostress soft rock.(1)The typical cases of tunnel invert failure in China are summarized.It is concluded that groundwater,high ground stress and expansive surrounding rock are the main factors causing tunnel invert uplift deformation.The internal relationship between large deformation of soft rock tunnel and surrounding rock strength and initial geostress state is discussed.(2)Through on-site geological investigation and monitoring measurement,it is concluded that the main factors causing the tunnel invert uplift deformation include the tunnel crossing fault fracture zone,swelling of expansive surrounding rock,strength softening of base surrounding rock,high ground stress and invert construction defects.(3)With the help of FLAC3 D,the dynamic construction process of the tunnel under various factors is simulated.Combined with the field monitoring and measurement results,it is concluded that the reasons for the large deformation of the tunnel invert are the faults and the construction defects of the invert.The numerical simulation results show that the invert uplift deformation is positively correlated with the horizontal in-situ stress value,the softening degree and depth of the surrounding rock at the bottom of the tunnel,and it is greatly affected by the expansion of the surrounding rock at the bottom of the tunnel and less affected by the lateral expansion of the surrounding rock.(4)The control effect of floor grouting and micro pile on invert uplift is studied.It is concluded that when the floor grouting depth does not exceed the depth of plastic zone,the strength and bearing capacity of rock mass after grouting are not significantly improved,and the uplift deformation of invert is not significantly improved.The application of micropiles at arch foot and arch bottom can greatly reduce the plastic zone of arch foot and surrounding rock on both sides,which has good control effect on the uplift deformation of inverted arch.