| In recent years,with the rapid development of China’s economy,there are more and more traffic projects such as roads and railways connecting different regions.Due to the high altitude and mountainous terrain in the west of China,a large number of mountain tunnels have appeared in the process of traffic construction.Different from the previous tunnel projects in the central and eastern regions,due to the relatively complex geological conditions in the western region,there are many problems of large deformation of soft rock tunnels when the conventional support technology is adopted.Minxian tunnel is a control project of Weiwu section of national G75 expressway.The traditional standard design method is used to support the surrounding rock.In the process of tunnel construction,serious soft rock deformation disaster appears,which has a serious impact on the safety construction and construction cost of the tunnel.In min county in tunnel construction,therefore,facing in the process of complex soft rock tunnel under the condition of large deformation problems,in this paper,the integrated use of site investigation and testing,theoretical analysis,laboratory test,the physical model experiment,numerical simulation and field test,such as a variety of methods,the complicated conditions of strong weathering mechanism of carbonaceous slate the large deformation of surrounding rock of the tunnel are studied,based on this,advances a new type of soft rock large deformation control countermeasures,and has carried on the successful application in the field,a series of meaningful research achievements.（1）The surrounding rock mass of Minxian tunnel is very broken under the action of slabs,joints and fissures.According to rock mass quality classification of[BQ]system and RMR method,strongly weathered carbonaceous slate rock mass isⅤ（very broken）level of surrounding rock.（2）Based on the theory of elasto-plastic mechanics,a simplified elasto-linear softening-ideal plastic mechanics model considering the strain-softening characteristics of surrounding rock under uniform stress condition was established,and the expressions of the structural zoning range and stress components of surrounding rock of Minxian tunnel were obtained.The borehole acoustic wave method is used to measure the surrounding rock structure of the tunnel under the original support.The results show that the surrounding rock in the large-deformation section of Minxian tunnel is mainly divided into three zones:failure zone,plastic zone and elastic zone.The failure zone is about 0-4m from the surface of surrounding rock in the shallow area,the plastic zone is about 4-10m from the surface of surrounding rock,and the elastic zone is more than 10 m from the deep area（3）Using the similar finite element plate method,the large deformation characteristics and evolution process of surrounding rock of Minxian tunnel during excavation and tunneling are simulated.The results show that the distribution of stress in layered rock mass is not uniform,so is the load acting on the support system.At the right shoulder of the arch with the maximum deformation of surrounding rock,the maximum displacement is about 12 mm,and the corresponding actual displacement is 480 mm.This position is the key position of surrounding rock.The large deformation failure of surrounding rock in Minxian tunnel mainly experienced six stages of progressive development:local collapse of the face,deformation of surrounding rock,cracking of shotcrete,deformation and failure of steel arch frame,failure of initial support,large deformation of surrounding rock and cracking of secondary lining.（4）Based on field measurement and analysis,laboratory test,theoretical analysis and model test of a variety of means such as comprehensive analysis,reveals the influence min county main controlling factors to the stability of surrounding rock for the section of the physical and chemical structure of rock mass,the plate theory,joint and crack weak structural planes such as cause of layered slate physicochemical is min county and broken section tunnel in soft rock,the main reason of the large deformation of surrounding rock on the surface of the radial force is too small cause looseness damage range is greater than the length of the bolt support is the immediate cause of the original supporting unable to control the stability of surrounding rock.The mechanism of large soft rock deformation in Minxian tunnel under conventional support technology is the large deformation of thin layer rock plate structure driven by engineering force and the large deformation of jointly broken rock mass by extrusion.（5）Combined with field investigation analysis and laboratory test,according to the theory of soft rock engineering mechanics min county type of soft rock tunnel section for the physical and chemical-high stress-swelling（JHS）compound soft rock,markedly large deformation of surrounding rock mechanics is interaction of complex deformation mechanism driven by a variety of mechanisms,including“bedding to oblique,tectonic stress,gravity driven,molecular water absorption expansion”(ⅢCBⅡABⅠABdeformation mechanical mechanism).（6）The new high prestress main-passive supporting technology was put forward.Numerical simulation method is used to simulate and compare the control effects of different support technologies.The results show that the maximum deformation of the initial support reaches 450 mm under the original support technology.After replacing the heavy steel arch（HW175）,due to the increase of the bearing capacity of the steel arch,the maximum deformation of surrounding rock is reduced to 400 mm.When the normal bolt is replaced with 7 m anchor cable,the control effect of anchor cable group on surrounding rock is significantly improved,and the maximum deformation is reduced to about 300 mm.The results show that the 12 m anchor cable can significantly change the displacement field of surrounding rock,the maximum deformation of the tunnel surface is reduced to about 250 mm.The new“7-12-7-12”support system was formed after all the ordinary anchor cables were replaced with constant resistance anchor cables.Under the action of high preloading force,constant high working resistance and sliding energy absorption characteristics,the non-uniformity of surrounding rock deformation field and the deformation of surrounding rock were significantly reduced,and the maximum deformation was reduced to about 120 mm（7）The supporting scheme of“advance conduit+primary shotcrete+7m NPR short anchor cable+12m NPR long anchor cable+full section I20a steel arch+secondary shotcrete+C30 reinforced concrete permanent lining”was adopted to conduct field test in the tunnel site.The results show that the maximum initial support pressure decreases by 25%compared with the original support.60-70 days after lining pouring,the pressure of secondary lining tends to be stable,and the maximum pressure is only 0.226 MPa;The deformation of surrounding rock is significantly reduced.The deformation of surrounding rock tends to be stable 30 days after the completion of the initial support and when the lag face is 33m,the maximum deformation of surrounding rock is only 73 mm.The new high prestressed active and passive combined support technology effectively controls the large deformation of soft rock in Minxian tunnel... |
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