Study On Numerical Analysis Method Of Coupling Of Seepage And Stress Considering Crack Propagation

Numerical analysis of seepage field of high dams,underground caverns and other structures is one of the hot research topics.Under the continued high water pressure,the vast majority of concrete dam foundation,dam heel and dam body will produce cracks or make cracks developed,which will cause the change of seepage field.The problem of crack extension belongs to the variable boundary problem and needs to redraw the grid of analysis model,which makes the computationa efficiency low.At present,proper theory has not been proposed to solve the problem of crack propagation's effect on seepage field at home and abroad.Thus,in this paper,under the framework of equivalent continuous medium model and based on the same grid,the method of corrected coefficient of permeability tensor is put forward to study crack development's effect on seepage field.And then the combination this proposed method with mature theory of fracture model of crack band,could study crack development's effect on the coupling of seepage field and stress field.Main works and results ofthispaperincluded:(1)Based on the equivalent continuum model and equivalent flow principle,modified permeability tensor method is proposed and the permeability tensor matrix of the modified element is derived.To verify this method,using finite element software,numerical models with a boundary crack and models with a inner one are built,whose fractured elements'permeability tensor is defined by the above modified permeability tensor method.It shows that modified permeability tensor method feasible to study the effect of cracks on the seepage field.Finally,modified element size is changed to analyze the effect of element size on this method.To meet the precision requirement in engineering,from the view of seepage flux,fixed element size is not more than 600 times the size of the crack width;and from the view of pore water pressure,fixed element size is not more than 200 times the size of the crack width.(2)Using FORTRAN,USDFLD user subroutine of ABAQUS numerical analysis software is secondary developed to define field variables needed for the element permeability tensor.In this way,during crack propagation,the coefficient of corresponding element permeability tensor can be modified automatically by the application of corrected permeability tensor method.It is validated that the defined field variables can realize the automation of elemnt permeability coefficient correction through two simple comparative analysis models.(3)Based on mature theory of fracture model of crack band,UMAT user subroutine is coding to modify elastic matrix of corrected element by FORTRAN.Combining the modified permeability tensor method with UMAT,an engineering example is given to study the coupling of seepage field and stress field considering the fracture development,assuming that the crack is developed.The results show that whole wate pressure would come into the modified elements when the crack developing forward continuously.Whole wate pressure hugely affect the seepage field and stress field in the vicinity of the cracks,but has little impact on its remote areas.And its influence on the displacement field is smaller in the whole research domain.