Back analysis and rectification of a failed cut slope in the Southern Expressway

A failure occurred in a cut slope of the southern expressway where all the surface drainage measures had been implemented. The failure surface was shallow but it has disrupted three levels of berms. The debris of failure were quite dry. A close examination indicated that a cascade drain has cracked and water is leaking to the slope. There were five systems of joints in the rock and adversely oriented relict joints were identified during rectification work . The failure could have been triggered by infiltration of rainwater through relict joints , reduction of matric suction and development of pore pressure . Rectification process involved installation of soil nailing and cable anchoring together with long sub horizontal drains