| Under the trend of mountainous construction environment and complex geological conditions in highway construction,it is particularly important to carry out research on tunnel surrounding rock.Especially when the lithology of tunnel surrounding rock is argillaceous sandstone as a typical soft rock,the surrounding rock contains seepage water pressure and fracture zone,which is prone to large deformation and damage during tunnel construction.The purpose is to control the safety of tunnel construction,ensure the service life,and study the large deformation mechanism and control technology of tunnel surrounding rock crossing the fault fracture zone.Therefore,this paper takes shangjiashan tunnel as the research object,through the combination of theoretical analysis,indoor test,similar model test and numerical simulation,and based on the study of surrounding rock characteristics,further optimizes the technical parameters of tunnel excavation,and finally puts forward the control index of structure stratum deformation.The main conclusions are as follows:(1)Based on the weak fracture characteristics of argillaceous sandstone in shangjiashan tunnel,triaxial compression tests under different water content and confining pressure were carried out,and the stress-strain laws of argillaceous sandstone under different water content and confining pressure were obtained.Based on the in-situ stress distribution characteristics,the strength characteristics under the corresponding confining pressure conditions are selected.Based on this,the triaxial creep tests of argillaceous sandstone under different water content conditions are carried out,and the creep deformation laws of rock under different water content conditions are obtained.The creep damage model of argillaceous sandstone under different water content conditions is established by modifying the Westphalia model and introducing nonlinear elements that can characterize the effects of different water content factors.The splitting test of argillaceous sandstone was further carried out,and the tensile characteristics were obtained.The above laboratory tests have defined the mechanical characteristics of argillaceous sandstone and obtained the value of its strength parameters,laying a data foundation for later simulation analysis.(2)According to the field engineering situation,the deformation characteristics of tunnel surrounding rock are analyzed,and the deformation mechanism of surrounding rock is expounded.Considering the comprehensive action of deformation pressure,loosening pressure and seepage water pressure,the calculation expression of seepage water pressure of surrounding rock is introduced into Kastner deformation pressure and classical Caquot loosening pressure calculation formula.The functional relationship between plastic deformation pressure of surrounding rock and plastic loosening pressure of surrounding rock and radial deformation of section under the condition of considering seepage water pressure is established,and the characteristic curve of surrounding rock is obtained.According to the actual support parameters,the characteristic equation of the support structure is derived,and the support characteristic curve is obtained.The characteristic curves of surrounding rock and support are compared and analyzed.Based on the equilibrium point of surrounding rock pressure and support reaction force,the value of reserved deformation of tunnel surrounding rock under the action of seepage water pressure is finally obtained based on theoretical analysis.Based on the value of support reaction when reaching the equilibrium point,it provides a reference criterion for the optimization of excavation parameters in the next similar simulation test.(3)In order to further analyze the reasonable value of the reserved deformation,the similar model test for the optimization of the excavation parameters of the tunnel with broken zone was carried out.Firstly,the influence characteristics of the three excavation methods on the stress of the support structure are analyzed,and it is concluded that the three bench seven step excavation method is the optimal excavation method.Secondly,the influence characteristics of six different cyclic footage on the stress of support structure are analyzed,and it is concluded that the optimal cyclic footage is 1m.On this basis,combined with the value of reserved deformation of surrounding rock obtained from theoretical analysis,the influence characteristics of 6 different reserved deformation on the stress of support structure are analyzed.Finally,when the reserved deformation is 300 mm,it is the best,and the correctness of the theoretical analysis results is verified.In order to further explore the influence of the included angle of different fault fracture zones on the deformation of surrounding rock and support structure,the tunnel excavation tests of seven different dip angle fault fracture zones are simulated.The comprehensive comparative analysis shows that with the increase of the dip angle of the fracture zone,the sliding deformation trend of the tunnel surrounding rock along the fracture zone surrounding rock interface increases,and the tunnel is more prone to instability failure.(4)Combined with the stress characteristics of the supporting structure under the influence of different excavation parameters obtained from the similar model test,the surrounding rock of the tunnel under three different excavation methods and seven different cyclic footage excavation parameters is simulated and analyzed by using the numerical simulation method.The vertical and horizontal deformation characteristics of surrounding rock and the distribution law of plastic zone under different sections along the tunnel axis are obtained.Finally,combined with the stress characteristics of similar model test support structure,from the two angles of structural stress and surrounding rock deformation,it is determined that the three bench seven step excavation method is the optimal excavation method and the cyclic footage of 1m is the optimal.According to the deformation range of tunnel surrounding rock under the optimal excavation parameters,it is verified that the reasonable reserved deformation value is 300 mm.Further simulation and analysis of tunnel excavation in fault fracture zone with seven different dip angles show that with the increase of dip angle,the sliding force along the fracture zone surrounding rock interface increases,and the interface anti sliding force decreases.Finally,the overall displacement and deformation of tunnel surrounding rock increases,and the area of plastic zone also increases.(5)Considering the weak characteristics of surrounding rock,after the lining construction,the surrounding rock is prone to creep deformation during the long-term operation of the tunnel,which will further cause additional deformation of the lining structure.Therefore,this section analyzes the creep deformation characteristics of weak surrounding rock based on the indoor creep test results mentioned above.On this basis,FLAC3 D is used for long-term simulation calculation,and the arch crown settlement and two waist convergence creep curves are obtained.The results show that each characteristic point has the characteristics of attenuation constant velocity creep deformation in the simulation calculation time,and its final deformation value is in the range of 2mm-4mm.Taking the creep equation proposed above as the calculation method of long-term deformation of tunnel surrounding rock,it is relatively close to the calculation results.Therefore,the calculation method is reasonable.(6)Based on the optimal excavation technical parameters obtained above,different stress release rates are simulated and analyzed,and the deformation characteristics of different excavation steps under the condition of 0～100% stress release are obtained.Combined with the cusp catastrophe theory,the stress release rate of surrounding rock when plastic strain catastrophe occurs is 70%.Based on the stability limit state analysis of surrounding rock,the deformation of two types of lithology under the condition of 70% stress release rate is numerically simulated,and two different lithology limit displacement values are obtained.Based on the limit displacement analysis,the control benchmark classification of tunnel surrounding rock deformation is determined,and the deformation control indexes of different types of tunnel surrounding rock are given. |
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