A Shear Device with Controlled Boundary Conditions for Very Large Nonplanar Rock Discontinuities

• Published in: Geotechnical testing journal 2022-07, Vol.45 (4), p.725-752
• Main Authors: Jeffery, Michael, Crumpton, Mason, Fityus, Stephen G., Huang, Jinsong, Giacomini, Anna, Buzzi, Olivier
• Format: Article
• Language: English
• ISSN: 0149-6115; 1945-7545
• DOI: 10.1520/GTJ20210220

The shear strength of rock discontinuities is an important design parameter that is noted to be scale dependent. Historically, discontinuity shear strength and scale dependency studies have used small to medium size laboratory shear devices that accommodate specimens with a relatively small area (0.01 to 1 m2) compared to real discontinuities. In the literature, there is a limited amount of shear strength studies available on discontinuity surfaces with areas of several square meters. This is inherently linked to the challenging nature of performing large shear tests. As shear strength scale dependency is still a timely topic, there is still a need for conducting large scale direct shear tests to support research. To facilitate investigations into the shear response of large discontinuities, a very large shear device was designed and built at the University of Newcastle, Australia. The device is designed to accommodate 2 m by 2 m specimens and restrict rotation and translations of the top surface during shearing. This article presents the design and characteristics of the shear device, the process undertaken to create 2 m by 2 m mortar discontinuity replicas and the experimental results of the first series of direct shear tests conducted. The experimental results confirm the systems design for restricting undesired translations and rotations of the tested specimen surfaces and test repeatability.