Study On Mechanical Properties Of Intrusive Rock Alteration Zone And Large Deformation Support System Of Tunnel In Hard Mountain Area

The intrusive rock refers to the rock solidified by the hot magma invading the earth’s crust.When the pressure of the overlying strata is reduced,the magma in the asthenosphere will be drilled out and the rock formed by condensation in the depths of the earth’s crust.The alteration of rock is the exchange of matter and energy between ore-forming fluids of different properties and wall rocks under certain temperature and pressure.The Peridotite is igneous rocks,and early igneous rocks will form fissures in the cooling process,that is,igneous rocks with fissures will be crushed by subsequent igneous rocks(physical action)and hydrothermal(chemical action).A loose wall rock that forms a hydrothermal alteration zone.The serpentinization of some peridotite strata in An-Ding tunnel is serious,showing coarse-grained massive structure,soft and hard differences.geological exploration and advance prediction show that bedding is relatively developed,structural plane is disorderly,rock mass is relatively broken,self-stability is poor,and large deformation is easy to occur.In this paper,relying on the An-Ding tunnel project of Yumo Line of Kunming-Wanzhou Railway,the author aim at solving the problem of large deformation of intrusive rock alteration zone encountered in this tunnel.By taking the mechanical properties of rock itself as the starting point,using the analysis method of indoor test,theoretical analysis and numerical simulation,this paper attempts to reveal the mechanism of the large deformation of Serpentine Peridotite,and puts forward the corresponding support method.The main research contents and results are as follows:(1)The mechanical properties of intrusive rock alteration zone are studied,and the conventional mechanical properties of rock are analyzed by uniaxial compression test and triaxial compression test.The results show that serpentinized peridotite is weak,and the mechanical properties of different samples have high variability and high water softening.Serpentinized peridotite has fatigue damage and high creep.Creep can be divided into three processes: deceleration creep,constant velocity creep and accelerated creep,and there are two thresholds related to spherical stress and partial stress.the first threshold is the creep opening threshold,before which only instantaneous deformation occurs,deceleration and constant velocity creep occur after arrival,in which the rate of constant velocity creep is proportional to the stress level.The second threshold is the threshold of accelerated creep,and the deformation of rock will increase sharply after the opening of accelerated creep.(2)The rock combination mechanics model of intrusive rock alteration zone is obtained from the creep properties of rock,and the mathematical viscoelastic-plastic constitutive model of rock is obtained by solving a series of differential equations.The results show that the rheological model of serpentinized peridotite is a viscoelastic-plastic rheological model with nonlinear Newtonian body,which is composed of a Brugers-like viscoelastoplastic body and a nonlinear viscoplastic body in series.The two plastic bodies of the combined model correspond to two creep stress thresholds respectively.(3)Combined with the field measurement data and numerical simulation of the project,the cause of the large deformation of soft rock in the intrusive rock alteration zone is obtained,and the control effects of various support methods on the large deformation of the tunnel are comprehensively analyzed,finally the supporting measures suitable for this project are put forward.The study shows that reason of the large deformation of Serpentinized Peridotite is that the wall rock has low elastic modulus and poor strength,which is easy to produce large deformation after excavation.The strong stress redistribution caused by excavation in the high geostress area leads to the accumulation of higher stress level in the rock mass,accelerated creep occurs after exceeding the creep threshold,and the wall rock deformation increases rapidly and becomes unstable.(4)The key to control the large deformation of serpentinized peridotite wall rock lies in how to reduce or delay the increase of wall rock stress level.Construction methods such as bench method,fast excavation and quick support can be adopted.Measures such as strengthening supporting structure such as long bolts or certain pre-strengthening measures can also be taken.