Research On The Strength Characteristics And Macro Mechanical Parameters Of Jointed Rock Mass

Since rock mass contains a large number of structure planes with complex distribution forms, the mechanical property of rock mass is often effected by structure scale and exhibits serious inhomogeneity, discontinuity and anisotropy. Determining mechanical parameters for rock mass has been topics of research over the past several decades. At present, the common practice in tunnel engineering is to determine parameter values according to the surrounding rock classification in field together with the values recommended in current codes, which may result in the designed engineering unsafe or too conservative, due to the large value range recommended in current codes. Based on extensive field work, a methodology that can produce fissured rock mass samples using a small-scale test equipment, was proposed in this paper. After considering the applicability of Barton-Bandias empirical formula, a method for analyzing the size effect on shearing strength of rock structure plane based on the JRC (with a length of 10 cm) measured in field and rebound tests on the surface of structure plane, was proposed by using two-dimensional discrete element software UDEC. The accuracy of the method was verified. Three-dimensional curved surface to describe the height variation of structure plane was developed using Weierstrass random fractal functions. The directionality of shear strength was analyzed by using three-dimensional discrete element software 3DEC. It was concluded that the difference of shear strength in different directions was more than 10%. The anisotropic characteristics of jointed rock mass were systematically analyzed by numerical experiments. With the increase of confining pressure, the anisotropic characteristics of the single-structure-surface rock mass disappear but the difference of strength is increased. Based on indoor mechanical tests on rock samples with different diameters, the analysis method for rock size effect was provided. The method of determining the physical and mechanical indexes for jointed rock mass was proposed as follows:1. Generalizing the engineering geological models obtained by engineering geological investigation in field;2. Selecting representative rock and structure plane;3. Determining the physical and mechanical parameters for rock and structure plane by laboratory tests and field measurements;4. Simulating rock mass by establishing numerical calculation model.Based on analysis results, it was verified that the method proposed in this paper can provides an accurate prediction of the physical and mechanical indexes for jointed rock mass.