Study Of Rock Experience Strength Criterion

The strength of rock mass is one of important contents carried out by rock mechanics , and empirical rock failure criteria study the subject by means of test in purpose of engineering .The paper devotes to it from several aspects as follows on base of test data and amounts of references :The paper first shows rock failure microcosmic mechanism affected by minerals and slight crackle in rock due to attain no enough understand to rock failure from macroscopic aspects. It is thought that a strength criteria should be the form of power function.Based on the criteria for rock mass classfied by empirical Hoek-Brown failure criteria, the paper discusses the subject from three aspects: intact rock, jointed rock,rock mass with discontinuities.Firstly, empirical criteria for intack rock such as Bieniawski criteria , Hoek-Brown criteria and Balmer criteria are analysed by means of triaxial test data . It is found that Balmer criteria not only fits trixial test data best among the three equations,but also gives a estimation values of.However ,the equation has also its disadvantages ,for example the three unknows and b are not easily solved, and the value of is often underestimated. Thus modification of Balmer equation is given to avoid its disadvantages.There are different viewpoints about the influnce of the intermediate principle stress on strengh of rock .It shows that the intermediate principle stress has effect on strength of rock through analysis of trixial test data. a strength criteria in power function for rock may not be adopted .Here a theoretical rock failure criteria ,twin shear strength criteria is showed in brief.It is thought that the strength of jointed rock masses lies between the strength of intact rock and the strength of rock mass with discontinuities,and is related to rock classification indices.In this paper ,several important rock classifications are showed throngh comparision of some references .Then some strengh criteria of intact rock talked about are used for jointed rock mass through modification of their parameters , which are related rock classification.When talked about anisotropic rock ,It often refers to rock mass with discontinuities. Obviously ,the strength of such rock mass is related with property of discontinuity, and shear failure is mostly characterized. This paper shows shear failure criteria of four different rock mass with discontinuities . Besides, it is possible for such rock mass that failure pass though the intact rock material . Here gives the conditions through the intact rock material on base of single set weakness plane theory. Then failure ways of two sets weakness plane are discussed . With amounts of weakness planes increasing , rock mass displays strength characteristic of isotropic rock material. It is so-called jointed rock masses in question .