Key Technology Study On Qingdao Jiaozhou Bay Subsea Tunnel Crossing Seabed Fault Zone

With the rapid development of economic and society,subsea tunnel as an important mode of transportation has attracted more and more attention around the world.Due to the seabed fault fracture zone,the tunnel construction will inevitably cross the fault fracture zone,where gushing water is very likely to occur at the same time beacause of the instability of surrounding rock,which will bring large potential risks to the tunnel construction.So how to cross the fault fracture zone safely is the key problem of the tunnel construction and also the key technology of promoting the development of the subsea tunnel.In this paper,the domestic and overseas literatures are reviewed,the Qingdao jiaozhou bay tunnel as the main engineering background,combining theoretical analysis,numerical simulation,field monitoring and other research methods,we conducted a systematic and deep research about comprehensive evaluation of surrounding rock and the physical and mechanical parameters of rock mass,the reinforcement effect and its in advance grouting water plugging reinforcement construction technology in tunnels crossing the fault fracture zone,which has formed key technology system of the tunnel through the fault fracture zone grouting water plugging reinforcement construction.And this leads to the following main conclusions:(1)The fault fracture zone crossed by tunnel can be roughly divided into four types:?the fractured zone with chloritization pieces,giving priority to pressure and torsion.?the fractured zone with diabaseprophyrite highly weathered detritus,giving priority to tension and torsion.?the fractured zone with unconsolidated or weakly consolidated rock with hard and soft broken objects,giving priority to compact mosaic structure and hard structure plane.?the fractured zone with consolidated rock.And the stability of surrounding rock of the four types of fault fracture zone are analyzed.(2)The rock mass quality evaluation results are obtained by using the BQ,RMR and Q classification system,and with the comparative analysis results of the three systems,comprehensive evaluation method is proposed to the tunnel surrounding rock classification evaluation,and at the same time the recommended values of the design and construction of the evaluation of the surrounding rock can be given.The segmented rock mass quality value and main suggested values of mechanical parameters of rock mass can be obtained with risk analysis of Q system of rock mess in each section.(3)In consideration of the groundwater seepage and advanced reinforcing effect on the stability of tunnel surrounding rock,the tunnel advanced reinforcement characteristic curve calculation method is proposed.On the basis of the existing Fenner solution,elastic-plastic solution of the subsea tunnel is deduced considering the seepage field and reinforcing ring of surrounding rock.And the solution is compared with numerical solution,which verified its correctness.(4)Through the study of the seepage model of the fractured rock mass and the properties of the grouting and its dispersion characteristics in fractured rock mass,it is concluded that fractured rock mass grouting effect is not determined by the single factor.Crack opening,crack obliquity,rock fragmentation degree,the grouting pressure and wide tension fissures have significant effects on the grouting diffusion range.(5)With the numerical simulation,the recommended values of grouting parameters in the construction of the tunnel crossing the fault fracture zone are obtained.When grouting in unfavorable geologic bodies with fault fracture zone,the grouting pressure of 3MPa,the grouting distritution distance of 4m in single layout can basically meet the needs of the curtain grouting;When faced with extremely fractured rock mass,with wide fractures,fracture dip against grout diffusion,the crack opening large and other adverse situations,the grouting pressure increasing to 4MPa and the grouting holes in single layout can ensure that the grouting effect;If using whole section grouting,grouting pressure of 3MPa,grouting distributed distance of 4m,and row spacing of 3m with Plum blossom hole pattern can ensure the grouting effect.(6)According to the characteristics of the tunnel in combination with field test,grouting effect test method of the fault fracture zone of the subsea tunnel is divided into five major categories,and the corresponding evaluation indexes for each inspection method are given.Based on the analysis of formation and grouting effect testing method,the "five parameters" grouting effect evaluation standard for judgment of grouting effect level is proposed.(7)The method of peripheral curtain grouting is taken in typical cross section of the channel tunnel in Qingdao jiaozhou bay subsea tunnel.Based on the mechanism of grouting reinforcement and grouting research results,grouting parameters and grouting material can be selected,superfine cement grout is chosen as the grout material.After the completion of the grouting process,the grout is mainly filling along the fissures,hard and soft interface and soft layer,with no contraction after solidification and the water plugging rate is about 96%,which means that the grouting reinforcement effect selected is efficacious.