甘肃北山花岗岩裂隙几何学特征研究及岩石质量初探

GEOMETRICAL CHARACTERISTICS OF FRACTURES AND ROCK QUALITY ASSESSMENT IN GRANITE IN THE BEISHAN AREA, GANSU PROVINCE

文中以甘肃北山花岗岩中发育的构造裂隙(主要指节理)为研究对象,通过野外裂隙调查,应用传统的概率统计方法与分形几何学理论,利用Mapinfo,ArcGIS平台进行裂隙几何学参数(方位、长度、密度等)的统计、计算和裂隙网络的空间结构分析,研究花岗岩岩体中裂隙的几何学特征。并以此为基础,对甘肃北山花岗岩岩体质量优劣进行初步评价。结果表明:在10～200cm范围内,裂隙网络是分形的;5个测点裂隙网络的分维值分别是1.636,1.548,1.596,1.724,1.604。分维数D不仅能刻画岩体中结构面发育的数量,而且能反映结构面在岩体中分布的均匀程度和交切方式。因此,可以表征岩体的质量优劣,对岩体质量进行分级。按照分维所划分的岩体质量分级,北山花岗岩属于裂隙较发育、岩体质量等级一般的岩体。

Geometrical parameters of fractures developing in natural rocks, such as density, dominant orientations, length, fracture aperture, are long recognized by engineering scientists because they are not only important parameters to fluid dynamics of fracture systems but also main considering factors for large-scale projects during construction and stability analysis. In this thesis, as a candidate area for high level waste repository （HLW） in China, the rock mass fracture system of the Bantan unit granite of the Jiujing block in the Beishan area, Gansu province, is chosen as the study object. The fracture system is studied in detail by field bedrock outcrop fractures surveying and combining the completed regional geological survey results with acoustic borehole television measurements. Traditional probabilistic statistics and the fractal theory are used to analyze the fracture geometric parameters including fracture length, azimuth and density. Statistics and calculation using the ArcGIS software are made to study fracture distribution characteristics in the granite rock mass. Quantitative description of fracture geometrical parameters is performed in order to provide necessary basic data for the selection of HLW. In the same time, by combining fracture density with fracture network spatial structure and using fractal dimension, the quality of rock mass of the Bantan unit granite is assessed. Fractal dimensions not only describe fracture number of rock mass but also reflect homogeneous degree of fracture distribution and the intact and cracked conditions. So rock mass quality classified by fractal dimensions combined with RQD is more objective and efficient than single RQD index. Above research indicates that the fracture network is characterized by fractal distribution. Fractal dimensions of five sampling sites are in turn 1. 636, 1. 548, 1. 596, 1. 724, and 1. 604, respectively, and fall into the range between 1.5 and 1.75. According to the rock mass quality classified by fractal dimensions, the Bantan unit granite belongs to rock mass with fracture well developed and normal quality.