Large Deformation Prediction Of Sericite Schist Tunnel In Western Yunnan Research On Construction Control Technology

With the development of transportation infrastructure in southwest China,more and more "long,large and deep" mountain tunnels are emerging,and the complex geological environment conditions in the tunnel area often induce various geological hazards.In this paper,the prediction theory and construction control technology of large deformation of the sericite schist white stone tunnel under construction in western Yunnan are studied.According to the prediction results of large deformation,the control technical measures are put forward,which is of great significance to the construction of similar tunnel projects.The research work and achievements of this paper are mainly divided into the following aspects:(1)The geological and hydrological conditions in the tunnel area are investigated.The surrounding rock of the tunnel is sericite schist.It is found by X ray and electron microscope that the rock is lamellar granular metamorphic structure,and its minerals are mainly granular metamorphic quartz and sericite.The maximum horizontal principal stress is8.07～8.77 MPa,the minimum horizontal principal stress is 5.72～6.36 MPa,and the vertical principal stress is 7.98～8.34 MPa,The direction of the tunnel axis intersects with the maximum horizontal principal stress in a large angle,which is unfavorable to the stability of the tunnel after excavation;According to the field needle penetration test,the rock strength is about 2 MPa,which belongs to very soft rock.According to the above test results,it is considered that the surrounding rock classification of BQ method has strong applicability,and the surrounding rock classification of Baishitou tunnel is divided into V grade.(2)According to the following investigation,the main geological hazard types of Baishitou Tunnel are as follows: extrusion deformation,arch settlement and arch convergence of the whole section of the side wall drum,mud inrush water,and from the DK163 DK163 840.DK163 The deformation law of Baishitou tunnel is revealed in the monitoring of the displacement around the three sections of 940.It has the characteristics of large deformation rate,long deformation duration,large accumulative displacement,significant settlement of the vault and asymmetry of the left and right deformation of the tunnel.(3)Combined with geological investigation,mineral composition and contentanalysis,in-situ stress test,rock penetration test,surrounding rock classification,large deformation and failure characteristics of surrounding rock,the large deformation mechanism of Baishitou soft rock tunnel is attributed to the large deformation under the condition of relatively high in-situ stress.Its main manifestations are:plastic flow of soft rock,structural bias,artificial disturbance mechanism.(4)On the basis of the analysis of the geological hazard characteristics,the variation law of the displacement around the tunnel and the large deformation mechanism,seven creep models are derived based on viscoelastic mechanics.The H-K-N model is accurate as a large deformation prediction model,and the DK163 of the tunnel is obtained by substituting the relevant parameters of the tunnel DK163 At about 300 mm,the deformation of the dome is close to that of the dome.(5)According to the prediction results of large deformation in each section of Baishi tunnel,the disposal measures to be taken in the section of large deformation tunnel will include strengthening geological advance forecast and mastering the geological situation of surrounding rock.Strengthen the management of monitoring data and strictly implement the monitoring and early warning system.Strengthen the disposal of deformation and invasion of surrounding rock.Strengthen the connection of locking anchor rod and optimize the type of supporting bolt.(6)To further analyze the effect of resin anchor on controlling large deformation,the traditional mortar anchor is replaced by resin anchor,and the surrounding rock displacement and anchor stress are analyzed under the original design condition,the anchor bolt is infilled to 0.7 m、0.4m condition and the anchor rod is lengthened to 6.0 m、7.5m condition.