Physical modeling of a rock mass under a true triaxial stress state

Abstract

A study was planned in which several (77 nos.) scale free 15 cm size block mass models having three orthogonal continuous smooth saw cut joint sets and varying inclination '0 ' of joint set-I with horizontal were tested in true-triaxial system (TTS) developed by Rao and Tiwari (2002). The specimens were prepared with Sand-lime brick model material of uniaxial compressive strength 13.5 MPa and representing 'EM' category on Deere-Miller's classification chart The test results show that with increase in a2 in dip direction of joint set-I, the strength of rock mass ^) and deformation modulus (Ej) increase significantly which is confirmed by fracture shear planes developed on a2 face of specimen, dipping in a3 direction and steeping with increase in a2 values. The strength enhancement was maximum (309.2 %) for inclination, 0 = 60° and minimum (24.2%) for 0 = 90°. The axial stress-volumetric strain curves show onset of dilatancy in rock mass and is increasing function of a2. Most of the specimens failed in shearing with sliding in some cases. The effect of interlocking (s) and rotation of principal stresses c2 and c3 on strength and deformation response was also investigated for few specimens with 0 = 60°. Finally, suitable failure criteria were also evolved in both triaxial and true-triaxial stress states.