The Compressive Strength Testing Method Of Broken Coal And Its Application In The Classification Of Surrounding

The uniaxial compressive strength of coal is one of the important indexes of surrounding rock classification.It is necessary to obtain accurate uniaxial compressive strength test results based on coal classification,strength grading and evaluation of coal roadway stability.At present,the research on the strength of coal is mainly focused on the complete coal sample test,and there is less research on the test method of broken coal seam compressive strength.In this paper,based on the method of field measurement,laboratory test and probability statistics,the expression of unaxial compressive strength of broken coal was obtained.In addition,by summarizing and analyzing the 847 groups of UCS data obtained grading and coal mass strength distribution.Ultimately,according to the specific coal roadway,it is suggested that uniaxial compressive strength value should be used in the classification of coal and rock mass.The main research contents and conclusions are as follows:(1)Due to low strength of coal core,the sample preparation is difficult.Thus,the relationship of weak coal between the critical pressure tested by borehole penetration method and UCS is studied by using a similar material simulation method in the laboratory.The fitting results of them have significant differences compared with more than 10 MPa test results.In order to obtain the test results of different diameter probes,they were used to test the strength of broken coal body by selecting 6mm,8mm and 10 mm diameter probes.In addition,by improving the probe diameter and the power type,the results showed that data correlation is enhanced with the diameter increases and the reliability of BPM is improved in the test of in-situ strength of broken coal.To determine the effective rate of 10 mm probe test is 79%,which solves the obvious problem of the probe leap in the test of broken coal.(2)The test method of uniaxial compressive strength for broken coal is proposed by regression analysis of relationship between the critical pressure and the point load strength index.a)The critical pressure of broken coal body was determined by the oil-pressure monitoring curve from the in-situ strength test.A point load testing device is used to test the point load strength index of irregular broken coal.The expression of regression prediction model between the critical pressure of borehole penetrating method and point load strength index is: Is50= 0.066 Pc-0.002.b)Based on the above model,the transformation formula of UCS and Pc is obtained by referring to the appropriate UCS and Is50 relations.Meanwhile,the distribution range of Is50 is 0.03~0.92 MPa,and the approximate formula is further selected.The expression of UCS of broken coal is UCS = 0.807 Pc + 1.726.c)The uniaxial compressive strength value of the broken coal is 2.97~4.53 MPa in the roadway of xinyuan coal mine.It is of great significance to support the surrounding rock and provide a basis for the broken coal roadway by obtaining the value range of the uniaxial compressive strength.(3)Based on large statistical data of uniaxial compressive strength value from broken coal and standard samples were analyzed by SPSS and 847 uniaxial compressive strength values were normal distribution.The mean value of the UCS of coal is 15.48 MPa,the minimum value is 1.37 MPa,the maximum value is 55.48 MPa,and the standard deviation is 8.93 MPa.By means of k-means cluster analysis,five categories of clustering results were analyzed and the grade of coal strength is classified into five categories: ?(1~10 MPa)??(10~15 MPa)??(15~25MPa)??(25~40 MPa)??(40~60 MPa).Compared with the uniaxial compression test,the point load test and borehole penetration method,the borehole penetration method can be used to test the different situation of coal body,which accord with actual engineering conditions,especially in the case of broken coal pillar roadway.In situ tested the coal strength of xinyuan mine roadway,it is concluded that the value of uniaxial compressive strength of coal is :6~15 points,which provides suggestions for the weight of UCS in the classification of coal rock mass.