| With the gradual deepening of the national strategies called “the Belt and Road”and the second round of western development,construction of transportation facilities in the western region is ushering a golden period of rapid development.Since in western region,mountains are steep and ravines are crossbar,and phyllite strata develop extensively,thus,it is inevitable that a large number of tunnels must be built through the phyllite strata.Due to their special characteristics such as low intensity,water softening,significant anisotropy and rheological behavior,tunnels easily meet deformation and failure phenomena including surrounding rock collapse,initial support erosion limit,secondary lining cracking and so on in the process of tunneling through the phyllite strata.It is a serious threat not only to the safety of construction workers and pedestrians,but also vehicles in the later stages of operation.Therefore,this essay is supported by the National Natural Science Foundation of China-Deterioration of tunnel structure in phyllite stratum and diagnostic study of lifetime service performance,the sub-project of the National Key Research and Development Program-Structural system identification,health diagnosis and life cycle performance evolution of long tunnel.It takes the means like laboratory tests,field tests,theoretical analysis,numerical calculation and others to do deep researches.From the perspective of macro-microscopic combination,six aspects of phyllite strata are revealed as follows: basic mechanical properties,rules of damage evolution,characteristics of energy evolution,rheological characteristics,failure mode of surrounding rock,damage characteristics of supporting structure.The main tasks accomplished are as follows:(1)A series of routine physical and mechanical tests are carried out systematically according to the mineral composition,microstructure,physical properties,Brazilian splitting,uniaxial compression,etc.,aimed to do in-depth analysis about its micro-structure,hydrologic properties,mechanical properties and modes of deformation and failure.Also,the combination of acoustic emission localization and digital speckle technique is used to reveal the structural characteristics of phyllite strata,as well as the rules of micro-damage derivation,distribution and extension under the influence of water from a microscopic view,so as to reveal the formation of anisotropy of phyllite strata and the mechanism of brittle ductility failure transformation.(2)Based on triaxial test results,it discussed the effects of stress state and structural plane angle on the mechanical properties and damage evolution,together with the weakening mechanism of water to physical mechanical properties of the phyllite strata.Furthermore,based on the continuous damage theory and the statistical intensity theory,sensitivity analysis of model parameters of the weibull distribution statistical damage model of phyllite strata was established to study the intrinsic meaning of model parameters and construct a statistical model of the rock masses damage with three factors coupling stress state,structural plane angle and water content.On this basis,the damage warning standard of surrounding rock of tunnels in phyllite strata is proposed.(3)This essay systematically carried out the uniaxial compression primary loading and unloading test of phyllite rocks under different water content and structural plane angles.Based on the energy point of view,the evolution law of energy(dissipative energy,elastic energy,total input energy)under different structural plane angles and water content conditions was analyzed.The relationship between structural plane angle,water content and rock compression energy storage coefficient is established.The evolution characteristics of energy indexes between soft and hard rock are analyzed and compared,and the new energy evaluation index of brittle ductility index is proposed.Also in this paper,the mechanism of brittle ductility conversion of phyllite under the influence of structural characteristics and water content is revealed from the energy point of view;The brittle ductility index is combined with the rock compression energy storage coefficient to establish a large deformation trend criterion for the phyllite tunnels that can fully characterize the energy evolution behavior before and after the peak.(4)Relying on the monitoring results of surrounding rock deformation and internal force in under-construction Wenma highway,this essay revealed the law of stress and deformation of surrounding rock and supporting structure,the law of bolt stress,and the load transfer law of initial support and secondary lining;It summarized the collapse of surrounding rock and the failure of initial support in the tunnel phyllite strata stratum section and put forward the deformation and failure mode of surrounding rock under the influence of structural characteristics of phyllite strata,and further analyzed the deformation and failure process of surrounding rock based on the coupling method of discrete element and finite difference.It modified PILE structure unit in FLAC3 D to give it a characteristic about shearing,in order to simulate the whole process of anchor shear deformation in anchor.C++ language was adopted to introduce the damage factor into the mohr-coulomb constitution and the statistical damage model that can reflect the damage effect of the whole process of initial support was obtained and combined with the modified PILE structure unit to build a numerical analysis model so as to reveal and analyze the damage evolution law of the initial support under different working conditions.(5)Uniaxial rheological tests of phyllite strata were carried out under different structural plane angles and different moisture content conditions so as to analyze the effects of structural plane angle and water on rheological properties of phyllite strata;Based on the original rheological constitutive model,it introduced a nonlinear viscoplastic bodies(NVPB)and anisotropy plastomer to build the constitutive model that could reflect the structural features of phyllite strata and nonlinear viscoelastoplastic rheology characterized by three stages,and the constitutive equation was generalized to three dimensional state with nonlinear viscoelastic plastic model theory,which became to the foundation to derive the constitutive model from finite difference form for secondary development and verified the correctness of this model.(6)Long-term monitoring projects such as bolt axial force,initial support and contact pressure of secondary lining,and internal force of secondary lining were carried out in the typical phyllite section of Wenma high-speed tunnel project.Based on these data,the characteristics of structure force variation under long-term effect of the rheological load were analyzed.The structural and rheological characteristics of the phyllite were proposed,together with the secondary lining cracking mechanism of the tunnel.In this thesis,a rheological anisotropy model based on discrete element was set up to analyze the secondary lining cracking characteristics under different working conditions.A nonlinear viscoelastic-plastic rheological constitutive model that reflects the structural characteristics of phyllite and the three-stage characteristics of rheology is used to establish a numerical calculation model under different working conditions,revealing the long-term damage evolution characteristics in secondary lining under rheological load. |
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