Experimental Research On Dynamic Characteristics Of Gravel Clay Core Wall Materials

The core wall rockfill dam has the advantages of wide material sources,simple structure and high design intensity,and is one of the dam types widely built at home and abroad.In the early stage,the core wall material was deformed greatly and its strength was low,and it mainly existed as a short dam;nowadays,earth-rock dams are developing in the direction of tallness.As a core material,gravel-doped clay can not only play the characteristics of low clay permeability,but also can play the characteristics of high mechanical properties of gravel,it has a positive effect on improving the stability of the dam,preventing arching effects and hydraulic splitting.At present,in core rockfill dams with a height of 200m or more,gravel soil is basically used as the core wall impervious material.On the premise of fully ensuring safety,China's dam construction technology has reached 300m high earth core rockfill dam,such as Lianghekou(293m),Shuangjiangkou(312m),etc.However,there are relatively few studies on the deformation and strength characteristics of gravel-mixed clay under dynamic action.In this paper,a small triaxial instrument is used to conduct dynamic modulus damping ratio test,permanent deformation test and dynamic strength test on gravel-mixed clay,main tasks as follows:(1)For different confining pressures and consolidation ratios,the dynamic modulus damping ratio test is carried out for gravel-clayed clay,to study the influence of the amount of gravel added on the mechanical properties such as dynamic shear modulus,the results showed that,the greater the amount of gravel,the greater the dynamic shear modulus of the soil.The amount of gravel mixing mainly improves the dynamic shear modulus under the condition of small strain,and the difference of the dynamic shear modulus of different amounts of gravel mixing in the later period is small.In this paper,the dynamic shear modulus is large before0.1%.At the same time,as the dynamic shear strain develops,the greater the amount of gravel,the greater the decay rate of the dynamic shear modulus.However,the shear modulus of the high gravel content has been more than that of the low gravel content.Therefore,the higher the amount of gravel,the stronger the resistance to deformation and the safer the soil.In addition,the higher the confining pressure,the greater the increase of the same amount of gravel,and the greater the increase in dynamic shear modulus.(2)Conduct permanent deformation tests on gravel clay,and study the basic change rules of permanent deformation,the results showed that,the residual shear strain and vibration times of the gravel clay are hyperbolic.Comparing and improving the Shenzhujiang model and the hyperbolic model,the data points of the hyperbolic model are fitted with less discreteness and more accurately reflect the law of soil changes.At present,there is no relevant model for permanent deformation of gravel-mixed clay.It is mainly referred to the permanent deformation model of rockfill for processing.It is recommended to adopt a hyperbolic model for gravel-mixed clay in the future.(3)Regarding the damage standard of gravel-mixed clay,there is no clear provision.Generally,the clay and gravel soil codes are referred to.Through the study of this paper,the reference to the code standards for certain working conditions will overestimate the dynamic strength of the soil.The dynamic strength test results show that,it is reasonable to take the rapid development of strain as the failure value:On the one hand,after the gravel-clayed clay reaches a certain strain,the strain begins to accelerate and the strain is less than the reference strain;On the other hand,different dynamic stress amplitudes are studied according to the research standards of this paper.The failure strain?_p is linear with the failure vibration number lgN_f,and the dynamic strength of different failure vibration number can be predicted;At the same time,compared with other standards,the relevant mechanical property changes are consistent with the reference specifications,and the safety evaluation is conservative.Comprehensive analysis,the dynamic strength failure standard of gravel-mixed clay,it is recommended to adopt the research standard in this article under equal pressure conditions,and the 10%strain standard under bias pressure conditions.