Rock Failure Pattern Under Uniaxial, Triaxial Compression and Brazilian Loading Conditions

Failure of rock is an important problem arising during underground construction of shafts, tunnels etc. It has been determined that the peripheral stress developed around a circular tunnel causes rock failure which makes it essential to recognize these failures patterns under these circumstances. Prediction and quantification of failure mode is very complex and difficult. Therefore, it is important to carry out comprehensive study in laboratory to determine rock failure pattern which is significant to stabilize engineering rock masses and to recognize the suitability of support system as per nature of engineering work. Uniaxial compressive strength, Brazilian tensile strength and triaxial strength tests were conducted on three different rock samples namely Migmatitic Gneiss (MG), Phyllitic Quartzite (PQ), and Quarzitic Phyllite (QP), collected from the vicinity of Rohtang tunnel in Higher Himalaya, to understand the nature of failure patterns. Test results shows axial splitting along with shearing along plane and multiple fracture patterns in phyllites and gneiss whereas gneiss also shows multiple fracture failure patterns with increase in comprehensive strength of rock under triaxial conditions. In case of Brazilian tensile strength tests failure pattern are generally of central multiple type. This paper highlights the failure modes of gneiss and phyllite rocks under different loading conditions using ISRM and BIS suggested methods.