Interaction And Stability Analysis Of Surrounding Rock And Lining Structure Of High Temperature Hydraulic Tunnel

With the continuous development and utilization of underground resources,the influence of high temperature environment on the stability of underground engineering has also been paid more and more attention,especially in the development of high temperature hydraulic tunnel,which is often accompanied by the coupling effect of multiple physical fields such as high ground temperature,high ground stress and seepage,so it is very important to study the mechanical problems of surrounding rock and lining structure during the construction of high temperature tunnel.In order to study the distribution of the plastic zone of the surrounding rock of the hydraulic tunnel and the stability of the lining tunnel in the high temperature environment,this thesis first relies on the field monitoring of a high temperature hydraulic tunnel in Xinjiang,and obtains the temperature distribution,geostress measurement data and mechanical parameters of the rock mass during the construction of the hydraulic tunnel.Then,based on the Mogi-Coulomb strength criterion and the elastic-plastic theory,the expressions of the stress,displacement and radius of the plastic zone of the surrounding rock-lining structure under the coupled action of temperature-stress and seepage-stress are derived respectively,and the effects of the main stress coefficient,temperature,seepage and lining structural parameters on the stress and radius of the plastic zone of the tunnel surrounding rock are analyzed by numerical examples.Based on the monitoring results and rock mass parameters,a multi-physical field coupling model of jointed rock mass under high temperature environment is built with the help of discrete element software.The development process of the plastic zone after tunnel excavation is analyzed by numerical simulation,and the influence of lateral pressure coefficient and joint occurrence on the distribution of the plastic zone under high temperature environment is studied.Finally,based on the above coupling model,the distribution law of plastic zone,stress field and displacement field of rock mass at different supporting time and the stress distribution of lining structure under different supporting schemes are further studied.The research results have important theoretical significance and application value for subsequent similarity engineering.Through the above research,the following conclusions are obtained:(1)It can be seen from the field measurement and analysis that:(a)The temperature of surrounding rock in the tunnel has basically the same trend with time,and the higher the temperature of surrounding rock is the farther away from the excavation face,and the lower the temperature is on the contrary.The maximum temperature of surrounding rock after the lining is applied is about 84℃,belonging to the high temperature tunnel section.(b)According to the hydraulic fracturing method,the maximum principal stress of this section is 19.9～22.2MPa,and the minimum principal stress is 10.2～12MPa.It can be determined that this section is a high stress area.(2)The intermediate principal stress coefficient,temperature,seepage and lining structural parameters have an impact on the distribution of plastic zone of surrounding rock.Considering the intermediate principal stress can give full play to the strength potential of rock mass: the radius of plastic zone decreases by 6.78% when the intermediate principal stress coefficient b=0.5 under the thermal coupling effect compared with that when b=0,and the radius of plastic zone decreases by 5.2% when the seepage-stress coupling effect occurs.The tensile stress caused by temperature change reduces the lining reaction by 14%compared with that under strong action only,and the reaction under seepage effect decreases by 58.1%.It can be seen that seepage has a greater impact on tunnel stability than temperature.When the concrete strength grade is increased,the reaction force is basically unchanged,so it can be seen that the concrete strength has little impact on the stability of the tunnel.With the decrease of the permeability coefficient of the lining,the support reaction will decrease and the radius of the plastic zone will increase.Increasing the thickness of the lining can obviously limit the development of the plastic zone of surrounding rock at the initial stage,but the limiting capacity of the lining thickness on the plastic zone of surrounding rock will gradually weaken with the increase of the lining thickness.(3)When excavating a circular tunnel in a jointed rock mass,the plastic zone tends to develop along the joint face to the deep rock mass,and the development degree of the plastic zone of the jointed rock mass is greater than that of the homogeneous rock mass.The development process of plastic zone after excavation can be divided into the following five stages: punctate plastic zone,annular plastic zone,partial plastic zone deformed development,plastic zone continuous deformed development and plastic zone deterioration.When the stress in the vertical direction is constant,the lateral pressure coefficient λ When increasing from 0.6 to 2.5,the shape of plastic zone is "butterfly","horizontal ellipse","circle","vertical ellipse" and "rectangle",that is,with λ With the increase of,the scope of plastic zone gradually changes from mainly distributed in the left and right sides of the tunnel to mainly distributed at the top and bottom of the tunnel.λ=1,the joint has the least influence on the plastic zone;λ The smaller or larger the plastic zone,the more obvious the uneven distribution of the plastic zone.(4)With the change of joint dip angle,the area of plastic zone will also change.When the joint is horizontally distributed,the area of plastic zone of surrounding rock is the largest,and when the joint is obliquely distributed,the area of plastic zone of surrounding rock is the smallest,that is,when the joint dip angle is 0°,the stability of surrounding rock is the worst.The smaller the joint spacing,the worse the integrity of the rock mass,the larger the area and displacement of the plastic zone formed after excavation,and the more unfavorable to the stability of the tunnel.(5)Through modeling and analyzing the distribution law of plastic zone,stress field and displacement field of rock mass at different supporting time,it is concluded that the earlier the supporting structure is applied after excavation,the better the stability of rock mass is;However,no matter what kind of support time,the stress in the lining structure is greater than its limit value and the damage occurs,so the secondary lining should be applied to ensure the stability of the tunnel.