Study On Seepage Control Effect And Stress State Of Cutoff Wall Under The Hidden Fault With Deep Overburden

In the western region,the hydraulic power resources is very abundant,but the unfavorable geological conditions such as deep overburden or hidden fault which often meet has strong permeability,which have the problems of permeability stability and leakage loss when the dam is built.Nowadays,concrete cutoff wall is applicated in deep overburden which can effectively solve the problem above.However,the cutoff wall is located in soft gravel foundation and also the hidden fault in the bottom make its stress condition extremely complex.If the cutoff wall broken down,the impermeability would be weaken,causing the hydraulic damage to occur,such as soil flow and canal gush,which has adverse impact on engineering.So it is necessary to analyze the seepage characteristics and stress condition of cutoff wall on deep overburden under the hidden fault systematically.Considering the soil constitutive model and the interaction of wall-soil resonably,the numerical simulation was used to conducted a systematic study of seepage control effect and stress state of cutoff wall base on Wayan reservoir earth-rock dam in Qaidam Basin with deep overburden and hidden fault.The main work is as follows:(1)Under consulting a large number of documents and related design specifications,the basic methods and principles of seepage control technology were summed up for gravel foundation and rock foundation,which could provide the referance for the choice of seepage control measures on deep overburden.(2)Basic theories of soil seepage analysis and related constitutive model were introduced and the secondary development function of ABAQUS was used to realize the application of Duncan-Chang E-B,which could provide a basis for the subsequent analysis of the seepage and stress dorformation.(3)According to practical condition of engineering,the three-dimension finite element model was built to analyze the seepage control effect of cutoff wall under the hidden fault with deep overburden systematically.Result shows that: Wayan reservoir meets the enginerring requirements with 70m-depth suspended cutoff wall.If the seepage coefficient of the fault is larger,the cutoff wall needs to pass through the fault and go deep into the dense rock mass.Or grouting can be used to reduce the seepage flow combining the cutoff wall.The cutoff wall should be avoided placing the bottom at the interface of two materials with wide difference of permeability to avoid local erosion because of the large gradient at the bottom of cutoff wall.(4)Combining the result of seepage analysis above,the three-dimension finite element model considering the interaction of wall-soil was built to analyze the stress state of cutoff wall systematically.It is pointed out that the existence of fault can cause stress concentration in the local position of cutoff wall,which has adverse effect on it.If the fault is broken and the integrity is poor relatively,Grouting measures can be used to improve the ability of resisting deformation of the fault,ensuring the stability of the cutoff wall structure.The research results can provide theoretical and technical support for the choice of Wayan reservoir’s seepage control measures,and also provide guidance and reference for dam constructure in Qaidam Basin with similar geological conditions.