Influence of discontinuities on the stability of cut slopes in weathered meta-sedimentary rocks

Abstract

The meta-sedimentary rocks along Pos Selim Highway in Perak State, Malaysia showed a gradational weathering profile based on differences particularly in textures, hardness, lateral changes in colour and consistency of material extension. Both large and small scale discontinuities observed in the investigated rocks reduce the physical and mechanical properties of the rocks, and provide slip surfaces for failures. Rock and soil samples were tested using established standards to determine their characteristics and responses under a wide variety of disturbances. Kinematic analyses were also carried out to determine the modes and likely modes of failures.

Petrographic analyses revealed associated micro-structures, and the implications of these micro-structures showed shearing components along planes of weakness. From the determined index properties of the tested soil samples, the weathered quartz mica schist is not suitable for structural support. Further study involving unconsolidated undrained direct shear box tests carried out under total stress, revealed a non-uniform response of the rocks to shearing disturbance along discontinuity planes, and the rate and depth of deformation. The shear strength components of the investigated rocks were thereby prescribed in terms of cohesion and friction angle. From the kinematic analyses across this extended cut slope, there are possibilities of wedge and planar failures.

Keywords:

• weathering
• rock index properties
• micro-structures
• shear box tests
• discontinuity planes
• kinematic analyses

Additional information

Funding

Special thanks to the University of Malaya for sponsoring this research through Postgraduate Research Fund, grant number: PS362/2010B.