The Joint Shape Determination in Rock Mass by the Statistical Simulation

Summary Geometry of joints or joint shapes is one of the geological characteristics, which is important for determining the strength and stability of rock mass. Here joint shapes mean the geometric forms of joints when looking from the direction normal to the joint planes. There is not enough literature and references about the shape of the joints. Some of them consider approximately the joint shapes as square, rectangular, circular or even elliptical forms. We usually observe the traces of joints as segments in rock outcrops but it is difficult to see their shapes in the outcrops of underground openings. In this research the parallel joints which form a joint set, are created by the statistical simulation for different joint shapes. Then by comparing the simulated joint distribution with the real joint set distribution from outcrop measurements, it is possible to predict the shape of joints in rock masses. The simulation results showed that the joint set distributions will not follow the classic statistical distributions such as logarithmic, power, exponential or Poisson. They are complex in nature and have a skewness to the left.
Introduction One of the important parameters of discontinuities in rock mass is the shape and geometry of joints. The effects of joint shape and its geometry in rock mass resistance properties are defined by many rock mechanics and engineering geologist specialists. They assumed the shape of joints as square, rectangle, circular and elliptical features.
Methodology and Approaches For determination the shape of joints in rock masses in this research the statistical engineering is applied. The joints and discontinuities are considered two-dimensional planes. Then by intersection of a random plane normal to the joint set planes the simulation of joints in outcrop were obtained. At the end by the distribution of the joints obtained from the simulation, one can determine the shape of the joints.
Results and Conclusions The results showed that the joints with circular, uniform shapes and with the relative movements have the exponential distribution of trace length. But for nonuniform cases the distribution approaches the normal distribution. A uniform distribution was observed for the square or the diamond shape of the joints.