The slope stability analysis using finite element method in the construction of Jragung Dam, Semarang regency-central Java

Abstract

The aim of this study is to evaluate the stability of the natural and designed cut slopes of the tunnel inlet and outlet portals at the Jragung Dam site, Semarang, Central Java, Indonesia, under static and earthquake loads using the finite element method. Input parameters used for the numerical slope stability analyses were obtain from surface and subsurface engineering geological investigations. The engineering geological investigations showed that the project area consisted mainly of claystone intercalated with sandstone and alternation of sandstone with claystone. The rock mass quality determined using the Geological Strength Index (GSI) indicated that the tunnel portal slopes consisted of very poor quality – fair quality rock masses. The numerical slope stability analyses using RS2 (Rocscience, Inc.), a finite element-based software, showed that the natural slopes at the tunnel inlet and outlet portals were relatively stable under static and earthquake loads. The designed cut slopes having a 50o inclination were found to be unstable even though the reinforcement has been applied. A further modification to the slope geometry and support measures were suggested. The designed cut slopes were found to be stable once the slope inclinations modified from 50° to 40°, and shotcrete and rock bolt reinforcement were applied.