ENGINEERING CLASSIFICATION AND INDEX PROPERTIES FOR INTACT ROCK

Physical and elastic properties of NX-size rock core from 27 localities were investigated in order to develop an engineering classification system for intact rock, and also to develop index properties related to important physical and engineering characteristics. Thirteen rock types are represented. Laboratory tests were conducted on these rocks as follows: unit weight, Shore scleroscope hardness, Schmidt hammer hardness, abrasion hardness, absorption, sonic-velocity stress-strain under cyclic loading to 5,000 psi, uniaxial stress-strain to failure, and point-load tensile strength. A total of 257 specimens with L/D ratios of 2:1 were tested. Statistical studies were conducted with the IBM 7094 computer to determine correlation and regression relationships for selected pairs of variables. A system of engineering classification is proposed in which rocks are classified on the basis of their strength and modulus properties either obtained directly from laboratory tests, or approximately from index properties recommended herein. Application of the proposed engineering classification system to data obtained by others is shown by individual charts for each of several different rock types. Five charts are presented for estimating the strength or modulus properties for intact rock from the numerical indices obtained by either the Schmidt hammer, the Shore scleroscope, or the sonic pulse velocity, all used in conjunction with the unit weight of the rock.