Determination of Cohesion values of Rock Materials using Double Shear Jaws

Abstract

IntroductionAlthough shear strength of rock materials is an important parameter for many different rock engineering applications, there is still a necessity for development of a standard method and details for determination of shear strength of rock materials. The conventional direct shear strength (DSS) test method suggested by International Society for Rock Mechanics and Rock Engineering (ISRM) and standards like ASTM D5607 are not a proper way to test high strength rock materials because of possible failure of cement mortar instead of rock core specimens [1][2][3]. The cement moulding method to hold specimens is more suitable for testing rock joints rather than intact rock materials. As another topic, the conventional DSS test has additional problems of impracticality in specimen preparation process including two steps cement mortar casting as seen in Fig 1. In this study, a practical test method for determination of cohesion values of rock materials is investigated to assess whether accurate strength values can be measured using double shear jaw (DSJ) which is a basic apparatus to test numerous specimens instead of only one specimen as in cement moulding method of holding. Within this purpose, new steel jaws for testing cohesion of rock materials were designed and manufactured in this study.Need for waiting the curing time of several days for holding specimens in the casted mortar method should be stated as another disadvantage of the conventional DSS test. As an important issue which prevents to measure the strength value under pure shearing, significant bending/tension effect is induced as the rock specimen loaded in the soft cement mortar. Having the bending effect in the specimen causes to measure smaller strength values than that determined under pure shearing condition [4][5][6][7]. In this study, a new method of using DSJ was investigated for the aim of having ideal loading condition. For the conventional DSS equipment in rock mechanics laboratories, manual load application by using the hydraulic jack is an additional lacking to cause a personal effect on the strength results. On the other hand, double shear jaws (DSJs) let specimens to be loaded vertically with a constant rate which can be supplied by the load controlled compressive equipment.

Determination of Mohr-Coulomb Parameters for Modelling of Concrete

“…A recently published paper showed a new interesting practical test method for determination of cohesion values of rock materials using double shear jaws [32]. Steel jaws are designed and manufactured for testing rock materials.…”