Abstract:

Rock quality designation (RQD) is the key parameter to evaluate the degree of fracturing of rock masses. There is error in rock mass evaluation when such factors as the scanline length and the scanline orientation are ignored.  RQD or joint parameters is obtained on the field two-dimensional rock outcrop, RQD of any scanline orientation in three-dimensional space is derived, and the variation of RQD with the scanline orientation is studied. It shows that the RQD is anisotropy both in the space or and plane. The authors put forward the N-A RQD calculate model that makes theoretical arguments more closely and the model assumed that the scanline from joints. Moreover, the Monte-carlo simulation is used to generate random values. Random values obeyed the negative exponential distribution with different parameters and were taken as the fracture spacings under varies of fractures development intensive degree. Then, the variation of mean and standard deviation of RQD values with the scanline length was studied by using four calculate models, i.e. T-T model, N-A model, A-A model and A-A-S model. By comparison, some results are concluded as the follows:1)the longer the scanline,the more accurate the RQD; 2)the A-A-S model can obtain the more accurate RQD when the scanline was short; and 3)a much longer scanline was necessary for the more credible RQD in more fractured rock mass.

Key words: RQD, scanlin method, scanline length, scanline orientation, anisotropy