| Under the new circumstances of regional economy integration and economic globalization,the planning and construction of the Belt and Road(B&R)has brought great opportunities and challenges for traffic and transportation industry in China.Massive transport infrastructure is being under planned and constructed in the western areas with complicated geological conditions,such as the large-spanned and deeply-buried long tunnels located in meizoseismal area are being constructed.During the process of tunnel construction,large deformation of surrounding rock,slabbing of rock,collapsing and breaking,rock burst,water inrush and burst mud and so on,have caused a high number of casualties and great property losses.Taking some carbonaceous phyllite tunnels located in the meizoseismal area of 5·12 Wenchuan earthquake as example,rock mass of carbonaceous phyllite was subjected to rubbing damage caused by earthquake and has bad geological properties,such as low strength,poor interlayer combination,joint fissures and distinct argillitization.Meanwhile,the carbonaceous phyllite has notable rheological behavior.Large deformation disaster during the tunnel construction has brought enormous challenges for the construction technology.This paper is based on the background of a deeply-buried long carbonaceous phyllite tunnel project.The tunne]located in the meizoseismal area of 5·12 Wenchuan earthquake,is a vital portion of the high speed railway from Chengdu to Lanzhou.Using the methods of laboratory test,theoretical analysis,numerical simulation,and field experiment,some value and significance results and conclusions are summarized as follows:(1)Based on the results of uniaxial tensile test,triaxial compression test and field experiment,the physico-mechanical properties and deformation characteristics of carbonaceous phyllite were researched.The deformation characteristics,happening mechanism,failure mode and influence factors for surrounding rock large deformation of carbonaceous phyllite tunnel located in the meizoseismal area was studied,respectively.The unstable failure mechanism of supporting structure in the large deformation conditions was analyzed.(2)Considering the initial microfracture damage and inherent characteristics of rock mass,based on the triaxial rheological tests data under different confining pressure,the coefficients m and n were introduced to appraise the initial inherent characteristics of rock mass,and some instantaneous plastic component was given to describe microfracture compaction deformation,and exponentially functional relation was established to express the relation between the failure stress rate and the strain rate.The transition judge rule from stable creep to the nonlinear viscoplastic accelerated creep was developed,and the stress threshold of judge rule was decided based on the initial microfracture damage and inherent characteristics of rock mass.Considering the immediate load level a?,nonlinear viscoplastic flow stress threshold vrs and initial inherent characteristics,nonlinear accelerated creep index ns were introduced and its linear function was established and the stress-strain relationship of function expression was derived.(3)The nonlinear viscoelastic constitutive model(INEVP)was established to describe the whole process of rock creep.This model could be used to describe the deformation of instantaneous elasticity(linear),instantaneous plastieity(nolinear),viscoelasticity(linear)and viscoplasticity(nolinear),and especially used to describe the instantaneous plastic deformation and nonlinear accelerated creep.Based on the results of loading and unloading triaxial rheological experiment of carbonaceous phyllite under different confining pressure,using MATLAB calculation software,parameters recognition of INEVP was applied with the nonlinear least square method.The basic principles of FLAC3D secondary development were analyzed,and the key issues of program composition were explained.Using FISH language,the calculation program of constitutive model mentioned above independently.Comparing the results of triaxial rheological tests,the effectiveness and applicability of INEVP constitutive model was verified.(4)Based on the three-dimensional numerical simulation model of tunnel,using the INEVP constitutive model,surrounding rock deformation law and distribution characteristics during the tunnel construction process with three-step method under traditional shaped steel support were analyzed.For different simulation conditions with different step length and support delay time,the time effectiveness of surrounding rock deformation was studied.The change law of pressure between surrounding rock and primary support under different simulation conditions with different support delay time were studied.The rational support time and yield deformation amount was founded.(5)Referencing the design method of frame-core wall structure used in super high-rise building,forming the deformation control strategy of "first release then resistance last rigidness"and "cooperation deformation",the SGCCT supporting system of steel grid-concrete core-tube frame were independent developed.The composition of the SGCCT supporting system was introduced and the characteristic of multilevel transformation assistant bearing load and deformation were summarized.The implement methods of quantificationally yield and yielding time controlling for SGCCT supporting system were presented.Using the analysis method of structural mechanics and the finite element software ABAQUS,the bearing behavior of new supporting structure was studied.(6)Selecting the stratums with high risk of surrounding rock large deformation,for common I-shape steel arch and SGCCT support structure,comparative test of field application was conducted.In the test,the settlement of surrounding rock,internal displacement of surrounding rock,pressure between surrounding rock and primary support,internal force of support arch,axial force of rock bolts,pressure between primary support and secondary lining,and strain of secondary lining in two different supporting structures were all measured and analyzed.The coefficient of lateral earth pressure and the ratio of average load carried by secondary lining to average load carried by primary supporting were calculated,respectively,which provided analysis foundation for the judgment of supporting structure safety.(7)The research achievements of this paper were successfully applied in prevention and treatment of surrounding rock large deformation disasters in some tunnel located in the area influenced by Wenchuan earthquake and Xiema tunnel belonged to the Chongqing expressway. |
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