Abstract:The joint size is the extension of the joint plane in space. For the joint Poisson disc model,the joint size can be represented by the disc diameter. Warburton¢s method is right theoretically,but not practical in determining the joint probabilistic distribution. A new method for estimating the joint diameter distribution is proposed without using the joint probabilistic distribution. With the variation of the initial mean values of the joint diameter,the relative errors between the initial mean values and the calculated values by the numerical method can be acquired. The relationship between the relative errors and the initial mean values is analyzed. When the error is zero,the optimal joint diameter is obtained by numerical method,and so is the joint diameter distribution. To verify the numerical method,two kinds of theoretical joint diameter distributions are adopted:negative exponential and lognormal distributions. The errors between the theoretical joint diameter and the calculated joint diameter by the numerical method are very small. The theoretical joint diameter distribution and the joint diameter distribution by the numerical method are uniform. The parameter analysis is implemented to determinate the available condition of the numerical method. Especially,the accuracy by the numerical method is better when the mean value of the joint diameter is relatively large and standard deviation is small. From the results above,it is concluded that the numerical method for calculating the joint diameter distribution is simple,valid and accurate. The numerical method is used to analyze the joint data of the statistical homogeneous domain II of the Jiji quarry-the preselected area in Beishan area,Gansu Province for Chinese high-level radioactive waste repository. The diameter distribution is acquired by using trace distribution from the multi-circular window sampling method.