Study On The Damage Of Tunnel Lining With High Water Pressure

Whether the concrete tunnel lining or other structures,the structural damage is mainly caused by the inner damage of concrete.There is a lot of concrete primitive micro-defects in the concrete,including micro-cracks and micro-holes,etc,which is the main cause of concrete damage.In external circumstance,since the different mechanical properties of its constituent materials and the adhesive surface between the constituent materials will expand and convergence,while the new generation of micro-cracks will continue to accelerate the destruction of concrete.During this period the concrete show some typical nonlinear mechanical properties: the inequality of tension and compression,anisotropic damage,stiffness degradation and so on.Degree of Concrete injury and damage state can be represented by damage variables.By introducing damage variable in the concrete damage constitutive relations can be considered the degree of development of micro-defects in the macro level,thus quantitatively evaluate the degree of deterioration of concrete structures.At present,most of the concrete damage constitutive models are obtained by fitting the experimental data with the limited scope of its application,there is no proper theoretical derivation,too.From the energy conservation of concrete damage,whether high hydrostatic pressure,or lining stress(although water pressure and lining stress for Injury way concrete are different),the stateunder the action of the energy consumed can be represented by concrete damage variable,all external factors acting on the concrete can be represented by ?.This paper introduces the present situation of theoretical research of concrete damage,and it does in-depth discussion on some key issues such as damage to the surface,the energy release rate and so on.And then based on thermodynamic principles and the existing experimental phenomena of conventional concrete damage constitutive model was developed and applied.The main work is as follows:(1)This part discusses the material composition of concrete and those mechanical properties of the different constituent components,analyzing of concrete meso perspective through its internal microscopic defects.Failure mechanism of concrete damage mainly in the interior of the micro-defects inherent in the role of external factors,the development,the results appear to accumulate macroscopic crack that structural damage.Concrete under uniaxial stress load strain development in theevolution of injury,damage characteristics of concrete to depth in the process of injury by typical concrete ?-? curve analysis.Thereafter,through the study of macroscopic concrete injury summarized the conventional concrete damage constitutive model and damage evolution,and to the introduction of the concept of concrete damage energy development,with an energy concept to characterize the degree of variation of concrete damage.(2)Damage theory several key problems damage variable,damage criteria and guidelines,and so do the plastic analysis and elaboration.Introduces irreversible continuum damage the basic principles of thermodynamics,we discussed the problem of damage variable selection,based on the energy extremum principle by Lagrange multiplier method to derive a theoretical model unified injury criteria and yield criterion of concrete,concrete injury and plastic two kinds of energy dissipation mechanisms are analyzed in detail.And in order to discuss the evolution of concrete injury.By analyzing and understanding the differences given in common understanding,poke a multilayer fog damage theory laid the foundation for later damage constitutive model.(3)This chapter is based on thermodynamic principles,and expanded the Helmholtz free energy into Taylor series,which make the inner material systems into variable mathematical functions.And without the strain equivalence hypothesis theory to establish stress-strain constitutive model,it improved its damage model,and orthogonal flow rule within variable to deduce suitable for isotropic elastic damage evolution equation,complete concrete elastic damage theory.Indirect evidence of nonlinear concrete material has some certain ability in the damage evolution.In the process of establishing an isotropic elastic constitutive model,the introduction of the damage variable associated with two first order Lame elastic constants,investigate their model is correct,and the elastic constants of Lame amended final results two damaging effects functions under tensor injury.The meso expression depends on the mechanical properties of concrete material damaging effects of function and its internal micro-defects geometric distribution.Not only provide binding sites for the macroscopic and microscopic damage mechanics continuum damage mechanics,but also reflects the characteristics of the interior material damage meso and macro link between the damage effects.(4)Based on irreversible thermodynamics,improved concrete elastoplastic damage constitutive model.In the effective stress space,using a single-sided yieldfunction considered unrecoverable deformation of concrete,fixed plastic Helmholtz free energy potential,making it more stringent to meet the thermodynamic compatibility criteria.Through the process of concrete damage elastic part,plastic part,damage part to analyses injury,and foundate a none related concrete damage constitutive model.(5)According to the water pressure of tunnel lining and surrounding rock pressure,based on the elastic constitutive model of concrete and the concrete elastic part of the elastic-plastic constitutive model,the porosity of concrete by Bernoulli equation with lining of pore water pressure and permeability,draws the concrete elastic constitutive model of complete damage description.