Study On Deformation Law And Control Measures Of Soft Rock In Deep Tunnel

At present,the number of highway tunnel is increasing,and some soft rock deformation problems will be encountered inevitably,including deformation of the tunnel face,convergence of the side wall,initial support failure,etc.In the construction of soft rock tunnels,the deformation problem of rock mass is often the key and difficult point.In order to ensure the normal construction of the tunnel,it is necessary to pay attention to the deformation state of surrounding rock at all times,take reasonable control measures in time,and stop tunneling if necessary.Based on the Meiya Tunnel of Zhengxi Expressway in Guizhou Province,this paper studies the deformation law,mechanism and control measures of soft rock in the construction of tunnel with two-step method by means of monitoring,theory and numerical simulation..The main study methods are as follows:(1)Geological and hydrological information of typical sections of the tunnel is collected,and selecting the typical sections for monitoring and measurement,and the monitoring data is used to draw the corresponding curve by means of regression analysis.It is concluded that the soft rock deformation of Maya tunnel has large deformation,long duration and large deformation rate.During the whole monitoring period of 46 days,the deformation growth was the largest in the first 10 days,and it should be applied as initial support in time,the deformation curve is like a step.After the second lining construction in the Meiya tunnel,the surrounding rock continues to deform,therefore,the second lining is not only a safe reserve for the tunnel,also with the initial support to bear the pressure generated by the surrounding rock.(2)According to the typical section regression analysis curve and the site construction situation,the construction deformation characteristics of the soft rock tunnel are analyzed,and the corresponding deformation mechanism is obtained.Then the deformation mechanism of the Maya tunnel is discussed from the factors of lithology,construction disturbance and groundwater.The main deformation mechanism of the Maya tunnel is the layered surrounding rock bending and weak interlayer extrusion.The main deformation mechanisms include lithology weakness,construction disturbance,rock mass stress expansion,physicochemical expansion and water weakening.(3)Based on the site engineering geological conditions of the Maya Tunnel,a finite element elastoplastic model was constructed using abaqus to simulate the double-hole parallel excavation of the Maya tunnel,and the evolution of the surrounding rock deformation and stress with the tunnel construction process was obtained,the deformation law of deep buried soft rock tunnel under the step method and the possible area of large deformation are summarized,and discuss the influence of the backward tunnel on the current tunnel deformation in the construction project.It is concluded that the vertical displacement of the vault and the arch bottom is large,while the maximum horizontal displacement appears in the left and right arch walls.Stress concentration is easy to occur at the arch foot.Since the meiya tunnel is excavated in parallel with two holes,the excavation of the rear hole will increase the excavation deformation of the first hole to some extent,which is mainly reflected in the horizontal displacement.(4)According to the deformation law and mechanism of soft rock tunnel,the control measures of surrounding rock deformation are analyzed,and the finite element elastoplastic model is constructed by using abaqus.The influence of excavation mode and support parameters on surrounding rock deformation during the construction of Meiya tunnel is discussed,including the restraining effect of upper step height,bolt length and section steel parameters on surrounding rock deformation.It is concluded that the height of steps on the typical section of Meiya Tunnel is about 4m,while the length of bolts is about 6m.The parameters of steel reinforced concrete should be determined according to the surrounding rock conditions in the tunnel site.Only by adapting them to each other can the effect of controlling the deformation of soft rock be maximized.