Inversion Of Surrounding Rock Parameters And Creep Analysis Of Deep-buried Diversion Tunnel Under Complex Geological Conditions

In recent years,China’s economic level and engineering strength have been continuously improved and the tunnel construction has gradually developed into the complex geological conditions,which have increased the construction risks.There are two main causes : firstly,the geological con-ditions and surrounding rock parameters are complex;secondly,the stabil-ity of tunnel structure is affected by the creep characteristics of sur-rounding rock.This article,based on the main channel project of the “Water Diversion Tunnel from Datong River into Huangshui River” in Qinghai Province,has drawn the following three conclusions by carrying out the inversion of tunnel surrounding rock parameters and the study of creep characteristics through the combination of machine studying and numerical simulation:(1)By summarizing the basic concepts and its five characteristics of rock rheology,comparing the analyzing several common component com-bination creep models,analyzing the deformation curve’s features of the surrounding rock.Finding that the creep characteristics of the surrounding rock in the F4-F5 section are consistent with the Burgers model.Therefore,the article introduces the Burgers model to carry out the follow-up studies.(2)An intelligent inversion model and analysis method combining multiple machine learning algorithms is proposed.In the light of the dif-ferent inversion targets(elastic modulus,Poisson’s ratio,cohesion and in-ternal friction angle),the author selected different kinds of algorithms to respectively construct intelligent fusion models,then performed inversion analysis of surrounding rock parameters through using the established fu-sion model.Through applying the obtained surrounding rock mechanical param eters to the forward calculation of FLAC3 D,the relative error be-tween the vertical displacement of the top and bottom of the cave and the horizontal displacement of the left and right sides of the cave has been achieved.The relative error value is small er than other single models,which shows that the proposed inversion intelligent fusion model and analysis methods are more reasonable and feasible.(3)This article establishes a surrounding rock-duck pieces three-dimensional numerical model containing sectional tunnel,excavating tunnels under creep conditions and performing long-term creep calculations.It is concluded that the variation patterns of the maximum principal stress and the minimum principal stress on the forward and backward lining cut-ting of the segment are basically the same.When the segment is above the tunnel,the maximum principal stress on the top of the lining cutting of the segment gradually changes from tensile stress to compressive stress,and the sedimentation value of the tunnel top continues to increase,while the uplift value of the bottom of the carve continues to decrease,leading the vertical deformation of the top and bottom keeping in the settlement status.In another case,when the segment is under the tunnel,the maximum principal stress on the bottom of the lining cutting of the segment gradually changes from tensile stress to compressive stress,and the sedimentation value of the tunnel top continues to decrease,while the uplift value of the bottom of the carve continu es to increase,which leading to the tendency that the hori-zontal deformation of the lining cutting of the center extending to the pe-riphery of the tunnel.