Research On Influence Of End Restriction In Coarse-grained Soil Tri-axial Test

The mechanics characteristic of coarse-grained soil is one of main research subject in soil mechanics.The coarse-grained soil is the main build material of the earth-rock dam,its mechanics characteristic from the test is essential foundation to build the dam.At present,mainly through large-scale triaxial test to study the mechanical characteristic of coarse-grained soil.Triaxial test is a kind of unit test,it’s considered that local stress at every point in the specimen is uniform under ideal conditions.However there is a certain friction between the specimen ends and the loading plate.Test conditions are often less than ideal state.This phenomenon is known as the effect of restriction in triaxial test.End constriction have led to the test result can’t reflect the real mechanical characteristic of coarse-grained soil.Therefore,in order to provide better protection for earth-rock dam,it’s meaningful to study deeply the effect of the end restriction of the large-scale traixial test.At present,engineering researchers use a variety of methods to reduce the end effect of restraint.But the result are not ideal.This paper adopted a new method of anti-friction,and did some contrastive large-scale traixial test.Researched the influence of effect of restriction,and demonstrated the validity of this method of anti-friction.New anti-friction method used a new loading plate.The new loading plate switched overall contact to distributed contact and sliding friction to rolling friction.Greatly reduced the friction between the interface.This paper selected representative soil,the new plate is used to do contrastive test.After the test,the specimens with end constriction are pressed drum-shaped.While the deformation of specimens are more uniform when the ends are free.Analysis of test data,end restriction has little effect on soil strength when the ratio of length to diameter is 2:1.It mainly influence the elastic modulus and deformation of specimen.In terms of elastic modulus,end restriction significantly increased the initial elastic modulus of soil(Nearly 100%).With the increase of confining pressure,the effect of end restriction gradually weaken.In addition,the effect of end restriction on elastic modulus gradually weaken with the development of axial strain.And the range of influence gradually narrow with the increase of confining pressure.In terms of deformation,with the increase of confining pressure,drum-shaped deformation that caused by end restriction gradually weakened.The deformation of specimen tends to be uniform.We can see the specimen deformation from the end of the test,the stress distribution within the actual specimen is not uniform because of the influence of the end restriction.In this paper,ANSYS finite element analysis program is used to establish the numerical analysis model.By setting different end restriction,get the contrastive stress distribution within the specimen,discussed the influence of stress distribution that caused by end restriction.Results showed that end restriction mainly affect radial stress distribution of specimen and less influence on the axial stress distribution.The influence of radial stress distribution is mainly focus on the end 1/4 region.