The Mechanism Analysis Of Deformation Of Concrete Under The Pore Water Pressure In Seepage Field

Currently,a number of super-high concrete dams have been built in China with water storage been completed.During the initial operation,the analysis of monitoring data shows that after the completion of impoundment the change of water level has a great impact on dam deformation,but the inversion results obtained by traditional numerical analysis method are not consistent with the monitoring results.After analysis,it is found that the main reason is that the traditional method of seepage load analysis is not suitable for mass concrete structures.For this problems,based on the stress-strain relationship of porous media in seepage field,comprehensively considered the meso-pore characteristics of concrete structure and the formation process of pore water pressure,this paper studied the mechanism of the effect of pore water pressure on the deformation of concrete structure,and obtained the law of the effective pore water pressure coefficient of concrete.After introducing the effective pore water pressure coefficient value,the paper analyzed the deformation law of concrete in seepage field by using the initial strain method of pore water pressure.Thus a reasonable numerical analysis method for the numerical inversion analysis of the deformation of concrete structure caused by the change of hydrogeological conditions is obtained.The research contents are as follows:(1)By analyzing the stress-strain relationship of porous structure in seepage field,it is found that the degree of influence of pore water pressure on the deformation of structure can be characterized by effective pore water pressure coefficient.It is also verified that the effective pore water pressure coefficient is 1 minus the ratio of macroscopic bulk modulus to matrix bulk modulus.Based on the above results,the relationship curves between porosity,pore shape and effective pore water pressure coefficient are analyzed by theoretical analysis,numerical experiments and laboratory tests.(2)The effective pore water pressure coefficient and pore water pressure are introduced as initial strain in finite element method,then the deformation law of pore structure in seepage field is analyzed.According to actual Engineering condition,it is concluded that the pore structure in seepage field is affected by seepage gradient force and pore hydrostatic pressure,which contribute to the deformation of the whole structure.However,for granular structure,the deformation is mainly caused by the dislocation between particles,and the compression of pore hydrostatic pressure can be neglected;for porous continuum,the effect of seepage gradient force and hydrostatic pressure on the overall deformation of the structure cannot be ignored.The essential difference of effect of pore water pressure in seepage field on medium deformation between porous continuous medium and granular porous medium is explained.(3)The pore characteristics and formation mechanism of concrete,as well as the law of internal water migration and water pressure changing,are studied.It is found that the voids in the coagulation are the main space for reserving and generating pore water pressure,and water is mainly transported to the voids through cracks and micro-cracks in the concrete.Because of the pore characteristics of concrete,when the hydrogeological conditions change,the effect of pore water pressure on the deformation of the structure will have timeliness.At the same time,due to the closure of the voids,the pore water pressure will be excessive or negative,which is reflected macroscopically as the impact on the concrete strength.(4)In view of the characteristics of the influence of pore water pressure on the deformation of concrete,the pore water element method is proposed in this paper,which regards pore as a solid element,and it has the mechanical characteristics of water when there is water in the pore.By the pore water element method,the influence mechanism of pore water pressure on the deformation of structure is analyzed from a mesoscopic point of view.Then,comparing with the laboratory test results,the correctness of the pore water element method is verified,which provides an effective method for the meso-analysis of concrete deformation in seepage field.(5)Based on the above results,the effective pore water pressure coefficient selecting method of concrete and the deformation law of mass concrete in seepage field are studied.Firstly,with theoretical analysis,numerical test and pore water element method,the validity of the effective pore water pressure coefficient selecting method is verified.The results show that the effective pore water pressure coefficient of concrete must be less than 0.5.Then,by comparing the results of the pore water element method with the results of the initial strain method of pore water pressure,the initial strain method of pore water pressure is verified as an effective numerical method for deformation analysis of mass concrete structures in seepage field.(6)Finally,the effect of water level change on the heightening of Hangzhou Lifan Dam is studied by means of the initial strain method of pore water pressure.Fully considering the mechanical parameters' difference between old and new dams,as well as the construction condition,the influence of water level change on the overall structural deformation of the heightened dam is explored.By studying the influence of seepage field on the deformation of the whole dam structure after heightening,the risk characteristics,safety and stability of the heightened dam are revealed,which can provide references for engineering practice.