Analysis of rough discontinuities resistance by laboratory determination under constant normal load (CNL) and constant NOMAL stiffness (CNS)

• Grant number: 17/06651-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2017
• End date: December 31, 2017
• Field of knowledge: Engineering - Civil Engineering - Geotechnical Engineering
• Principal Investigator: Marcos Massao Futai
• Grantee: Lucas Daniel Sales Veloso
• Host Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Discontinuities such as, joints, bedding planes, shale, zones of alteration or failure reduce the shear strength of the rock mass (Hoek & Brown, 1980) and (Barton, 1986). In general, this reduction of resistance affects the stability of excavations, located in a rocky massif. When a rock block enters a shear situation, there is a dilatancy in the direction perpendicular to the plane of the discontinuity and a deformation in this plane. Discontinuities, being less resistant than intact rock, can accommodate deformation only till a limit, after which the structure undergoes rupture. Shear strength of discontinuities can be determined by direct shear tests (Muralha et al., 2014). In most cases, these tests are performed under constant normal force (CNL), however this method simulates only certain specific situations in rock mechanics, such as unsupported rock slopes or rock structures with freedom of dilatation. For more general cases in which the boundary conditions restrict the shear dilatability, such as tunnels where the rocks are confined or supported slopes, constant normal stiffness (CNS) tests are more suitable (Leichnitz, 1885). The objective of this work is to evaluate the structural mechanical strength under CNL and CNS boundary conditions and compare the behavior of the structures in both cases. (AU)