Study and application of a method for rapid-determination of uniaxial compressive strength of weak coal in Xinyuan coal mine

Uniaxial compressive strength ( UCS) is one of basic parameters to measure the mechanical properties of coal and rock mass. It is extremely difficult to obtain the UCS of weak coals. Based on the current engineering back- ground of Xinyuan coal mine,this paper proposes a new borehole penetrating method for a rapid measurement of the UCS of weak coal. It provides a new idea to build a field measurement method of UCS of weak coal. By optimizing the probe diameter and improving the pump,the in-situ penetration strength of the broken coal was measured. Then the broken coal samples were collected for the laboratory point load strength measurement. The test data were divided into two groups according to two test methods of borehole penetrating method and point load method,and the corresponding test results were obtained with the relevant parameters of Weibull distribution. Statistical software SPSS was used to test the significance of regression equation and regression coefficient,then the relationship between the critical load (Pc ) and the point load intensity index (Is50 ) of the weak coal is derived at the Xinyuan coal mine. By virtue of the empirical relationship between Is50 and UCS,the relationship between UCS and Pc is established to realize the rapid in-situ determination of UCS of weak coal. The study shows that the Weibull distribution shape parameters correspond- ing to the test data of the drilling penetration method and the point load method are 4. 02 and 4. 12 respectively,which indicates the distribution function shapes of the test results of the two test methods are basically consistent;the relation- ship between the critical pressure of borehole penetrating method and the point load strength index of the weak coal body in Xinyuan coal mine is:Is50 = 0. 066Pc -0. 002;the distribution range of Pc is 1. 55-3. 48 MPa and the expres- sion of UCS of weak coal is UCS = 0. 807Pc +1. 726;and the uniaxial compressive strength value of the weak coal is 2． 97-4． 53 MPa in the roadway of Xinyuan coal mine. The results of UCS measurement of weak coal in Xinyuan coal mine match with the field estimations,indicating that the proposed method for conducting the UCS measurement of weak coal is feasible.