Study on construction stability of soft surrounding rock tunnel considering time-space effect

Taking Jiaxianggou tunnel in Dazhou-Chengdu high-speed railway as background,by using the finite-difference software FLAC3Dand Burgers rheologic constitutive model,the construction mechanical behavior of soft surrounding rock tunnel is studied.Variation laws and magnitudes varying with time and space of rock surrounding deformation and rock surrounding pressure and support structures bearing force behavior and internal force in an object cross section are attained.And the calculation results are compared with the field data.The study result shows that in the range of 1.5～2.0 times of tunnel diameter in the front of the excavation face and the range of（2.0） times of tunnel diameter of the back of the excavation face,the surrounding rock deformation is caused mainly by space effect.Rheological effect plays a key role on the deformation out of the influence range of the spatial effect of excavation face.Because of the rheological effect of surrounding rock,the surrounding rock pressures and the contact pressures between primary support and secondary lining and internal force and bearing force of support structures both vary with time.When the surrounding rock is excavated,internal force and bearing force of support structures increase very quickly,and then they become steady after arriving at a certain extent.After secondary lining is be constructed,internal force and bearing force of support structures increase at low speed.Finally,high-stress-zone of the arch foot,hance and inverted arch has high probability of failure.The experience and conclusions presented can provide reference to design,construction and research of similar tunnel.