Reasearch Of End Friction Effect Under True Triaxial Compression Experiments

With the rapid development of the global economy,the human demand for energy increases,and the exploitation activity of mines and mining depth also increase.As a reasult,practical civil engineering project gradually into deep rock engineering,subjected to complex stress state stage,encountered many engineering problems,such as in deep underground mining,some large-scale civil engineering and the excavation of underground tunnels,rock burst occuring frequently.The researchers found that past rock strength criterion has obvious flaws,recommending using a more realistic criterion,which takes into account the impact of intermediate principal stress.To examine these issues,a real true triaxial testing machines which can apply different load paths needs to be constructed.Therefore,Northeastern University,combining hot issues of international rock mechanics research,is carrying out project to study the true triaxial rock destroyed rules in the deep mining process.End effect is one of the most important technical problem to be solved before Northeastern University carrying out true triaxial experiments,as far as possible to achieve a uniform triaxial stress state.Although this issue is extremely important,researchers have also experimented with different friction materials hopes to achieve reduces the end friction effect,but the number of verification friction reduction related trials and studies indeed very small,especially no one on the side of quantitative analysis of the friction,and therefore not a good end friction understand and solve the problems.This paper from the intensity and deformation of two indicators to compare and evaluate end friction effect,early stage in conventional triaxial test machine platform do the end friction experiment of single loading,the method of multi-point measurement of strain to method to verify the feasibility.Then in really triaxial platform on the determination of the past for the true triaxial test in two commonly used friction reducing agent(teflon and stearic acid)of the friction coefficient,evaluation in true triaxial test machine of three different types of rigid loading test in the end friction effect(two different directions of the uniaxial loading test and biaxial loading),through the optical microscope observe the antifriction agent form.In the end,the influence on the strength and deformation of the two axial test in the three cases of the true triaxial test is compared.The effect of the end friction effect on the three axis test is discussed by using intensity difference value.