Study on Measurement of Shear Strength of Rocks

Abstract

The object of this study is to discuss how the shear strength of rocks, which is necessary for analytical, studies of rock fadure in drilling, blasting and in strata control, should be measured.
It is considerecithat the methods for measuring the shear strength may be classified following two. Namely, (T) rhe shear strength (I) is measured by the nominal stress (P-A), where P is the shearing force and A is the areo of the shear plane, and (2) the shear strength (II) is measured by the calculation of the stresses actina or the plane of shear fracture.
In this study, a double shear test was carried out for (I), and the Mohr's construction method, in which the shear strength would be found from intersection o fτ-axis and Mohr's envelope, was carried out for (II). The Mohr'senvelope is represented by the par Gbolic curve in this tast. And this Mohr'senvelope is guessed to be useful for measuring the shear strength in rock strata.
The results are as follows; the shear strength (I) by double shear test is calculated larger than that (II) bv Mohr's envelope, because the normal stress acts on the shear plane in the former test.Also, in the double shear te: st under the tri-axial pressure, the regularity of the sheared surfaces increases as the confining pressure increcses.