Experiment study on the regularity of the coal pillar residua based on the damage variables

The present paperis inclined to search for the regularity of the coal pillar residua setting-up based on the study of the damage variables.For this purpose,we have conducted the experiments to trace the relationship between the damage variable and the stressstrain in the course of the total failure process by using the damage variables which can be detected based on the constitutive model for the rock damage,but the damage variables have to be made wellsuited for explaining the damage degree of the materials.In addition,the method formeasuring the reasonable size of the coal pillar residua can be obtained by comparing the different damage variables of various coal pillars,whose evolution regularities can be summarized by using the method of quantitative analysis of the relation between the pillar size and the damage variable by the following factors:it is remarkable for the influence of width/height change on the damage variable,thatis to say,with the increase of the width and decrease of the height may lead to the damage variable decrease and peak value increase while the width/height ratio is2 by considering the peak value and the damage variable for protecting the coal seam.Thus,the damage variable with the strain can be described by the positive exponential function though the regularity between the damage variable and the strain can be deduced from the zero damage stage with the linear damage stage increase and stable damage stage prolonging.However,the stages may have different implications,that is to say,the zero damage stage is a process of consolidating the coal matrix,whereas the linear increasing damage stage is referred to as the micro-fracture emerging and fast extension.Moreover,it is necessary to point out that the stable damage stands for a state of complete breach of the coal pillar in the experiment.Thus,the relationship of the multiple linear regressions with the damage variable,peak value,width/height ratio and height can be used to denote a reasonable pillar size.