Study On The Creep Characteristics Of The Surrounding Rock Of Wudang Schist Tunnel And Its Influence On The Lining Cracking

This paper takes numerous Wudang group schist tunnels in the northwest of Hubei Province as the main research object to analyze the engineering geological characteristics in the study area,physical and mechanical characteristics of the surrounding rock of the relevant tunnel,also the creep characteristics with on-site investigations combined both indoor and outdoor experiments manners.The physical and mechanical parameters of the surrounding rock,long-term creep properties of the Wudang schist,as well as the certain creep constitutive relation and creep parameters of the Wudang schist is obtained,based on which creep mechanism of the schist is analyzed at microscopic level.Through theoretical calculations and numerical simulations,the influence of the creep characteristics of the Wudang schist on the cracking of the tunnel lining is studied.Finally,a treatment plan for the lining cracks of the Wudang group schist tunnel is proposed based on the field example.The detailed research results obtained in this paper are as follows:1.Geological survey is conducted on the Wudang Group strata in the northwest of Hubei Province,which contains the engineering geological conditions,stratigraphic lithology,topography and geomorphology,geological structure,and hydrogeological conditions of the study area.Also the characteristics of the Wudang thrusting tectonic movement is grasped;The hydraulic fracturing method is used to conduct a representative test analysis of the in-situ stress conditions in the study area.The in-situ stress parameters of the area is ackonwledged,and the ground stress field in the area is dominated by horizontal stress and belonged to the high-lying stress area;Uniaxial and triaxial compression tests is conducted on wudang group schist with three kinds of schistosity plane Angle(0°,45°,90°),and obtained the schist mechanical parameters,and three kinds of schistosity plane obliquity schist of mechanics parameters of each are not identical,which shows that wudang group schist has obvious anisotropy.The structural plane shear tests of the Wudang schist under natural and saturated conditions show that the shear strength index of the rock sheet in the natural state is obviously higher than that in the saturation state.2.Through triaxial compression creep test of the Wudang group of mica-quartz quartz schists,it is concluded that the deformation process of the sericite quartz schist under triaxial stress state includes instantaneous strain,decay creep,stable creep and accelerated creep.Under the condition of low stress level,the deformation is dominated by instantaneous deformation,and with the increase of stress level,the creep variable increases continuously.At the same time,the sericite quartz schist has obvious creep anisotropy characteristics.Under the same confining pressure conditions,the axial instantaneous strain and creep of the parallel group specimens are larger than those of the vertical group specimens;The nonlinear Burgers model is adopted to identify the whole course of rock creep,and the creep model parameters were obtained.The microstructure of the sericite quartz schist is obtained through the microstructure test of the Wudang Group sericite quartz schist.Accordingly,the sericite quartz schist is divided into cracks,hard parts and weaknesses.And four kinds of microstructural changes is proposed,including closure of open crack,position adjustment of weak part,micro-cracking and position adjustment of hard part.Based on this,the creep mechanism of sericite quartz schist is analyzed.3.The relationship between the surrounding rock of soft surrounding rock tunnel and the supporting function is discussed,so is the mechanism of the tunnel structure in surrounding rock and supporting structure of the soft surrounding rock tunnel;The elastic analysis of a circular tunnel under the action of two-directional differential pressure is presented,with the corresponding viscoelastic solution solved based on elastic-viscoelastic correspondence principle,the expressionp_i(t)of the interaction force of tunnel surrounding rock and lining structure with respect to time t is received.4.By means of numerical calculation methods,under the effect of creep in the schist rock in the Wudang Group,the law and characteristics of deformation and stress of the lining structure without the initial crack lining and initial crack lining in the tunnel operation in 100 years is studied.With the influence of creep in surrounding rock in Wudang group on rock lining structure cracking is summed up.The specific conclusions are as follows:First of all,deformation and stress characteristics of lining under no initial crack is studied,in the operation of 100 years.It is found that the tunnel displacement increment is large in the early period and the later increment gradually slows down within the 100years of tunnel operation,while still an increasing trend.The displacement in the vertical direction of the tunnel is obviously greater than the horizontal displacement.The maximum vertical displacement occurs at the top of the arch,as the maximum horizontal displacement occurs at the boundary wall;Under the effect of creep in surrounding rock,the axial force and bending moment of each part of the tunnel lining increase with time.The creep of the surrounding rock has a greater influence on the position of the arch leg and the arch of the arch,and the axial force and bending moment value of these two locations is greater than other parts.Secondly,the mechanical characteristics of the lining structure in the presence of initial cracks in different parts of the tunnel lining is studied.It is found that under the effect of creep of the surrounding rock,tunnel lining with initial cracks in different parts will increase comparing to these without initial cracks.Under the influence of surrounding rock creep,comparing to the lining without initial cracks,the presence of initial cracks in different parts of the tunnel lining will increase the axial force and bending moment of the lining structure,while the axial force and bending moment of the part where the initial crack exists is much larger.,the increments of other parts of the axial force and bending moment increments are small;At the same time,the existence of initial cracks in different parts of the tunnel lining will reduce the safety factor of the lining structure,so the lining structure reaches the safety factor threshold in advance.The safety factor of the site where the initial fracture exists is relatively small,while the safety factor of other sites is relatively small affected by the initial crack.Finally,the mechanical characteristics of the lining structure in the condition of tunnel lining with different depths of initial cracks is studied.Under the creep of surrounding rock in the schist tunnel,the initial cracks of the tunnel lining structure will increase the structural stress of various parts of the lining,the greater the initial crack depth,the greater the stress of each part of the lining structure.At the same time,the existence of initial cracks in the tunnel lining structure will reduce the safety factor of each part of the lining.The larger the initial crack depth is,the smaller the safety factor of the lining structure will be at the same time,while the time when the lining structure reaches the safety factor threshold.5.Combining domestic and foreign research results and on-the-spot investigations,the treatment process and plan for cracks in the lining cracks of expressway tunnels in Northwest of Hubei Province is proposed.The long-term monitoring of lining cracks is carried out in the case of Zhuxi tunnel lining cracking in northwestern Hubei province.The trend and law of cracks in linings is being predicted.Based on the monitoring results,a treatment plan for the lining cracks of Zhuxi tunnel is put forward.