Research On The Load Damage Effect Of Concrete Permeability

In practical engineering,concrete will be damaged and micro-cracks will appear under external loads,which will lead to the increase of permeability coefficient and affect the durability and bearing capacity of practical engineering.Therefore,it is necessary to establish the relationship between permeability coefficient and damage of concrete,which is the key to study the coupling of seepage and damage of concrete,and is of great significance to engineering application.In this paper,the relationship between permeability coefficient and damage variable of concrete is established by means of physical experiment at macro level,and then the relationship between permeability coefficient and damage variable of concrete with different aggregate content and gradation is obtained by means of numerical simulation at meso level.Finally,the relationship between the concrete permeability coefficient and the damage variable is applied to the engineering example,and the seepage-damage coupling analysis of the concrete gravity dam is carried out.The main contents and conclusions are as follows:(1)The concrete specimens with C20,C30 and C40 strength grades were subjected to uniaxial compressive peak loads of 0%,30%,50%,70% and 90% respectively.Based on the theory of damage mechanics,appropriate damage variables and damage models were selected to determine the damage.Then the permeability coefficient test is carried out to explore the influence of damage on permeability coefficient,and the relationship between permeability coefficient and damage is established.The results show that the permeability coefficient increases with the increase of damage,and the relationship between them is in accordance with the exponential function.(2)At the meso level,concrete is regarded as a three-phase composite composed of aggregate,mortar and interface layer.Based on random aggregate model,the program of elliptical two-dimensional random aggregate model is compiled with MATLAB software.The maximum aggregate size is 20 mm and 40 mm,and the aggregate content is 30%,40%and 50%,respectively.Then,the aggregate boundary is extracted with AutoCAD software,and the finite element model is generated by ABAQUS software.By applying different displacement loads to produce specific damage,and then conducting seepage analysis,the relationship between permeability coefficient and damage is obtained.The results show that the relationship between them is also in accordance with the exponential function.(3)Using the ABAQUS software,the relationship between the permeability coefficient and the damage is applied to the seepage-damage coupling analysis of the concrete gravity dam through the user subroutine USDFLD.The results show that the exponential function of permeability coefficient and damage can effectively simulate the seepage-damage coupling effect.Comparing seepage field,stress field and displacement field considering coupling with that without coupling,it is found that pore water pressure near dam heel increases significantly,stress concentration increases and damage area increases significantly after considering seepage-damage coupling.In addition,the horizontal displacement of dam top increases,the vertical displacement decreases,and the anti-sliding safety factor decreases,which is more adverse to dam safety.