Stability Analysis of Kelau Earth-Fill Dam Design under Main Critical Conditions

 

Mohd Ashraf Mohd Ismail

School of Civil Engineering, USM, Engineering Campus,  14300 NibongTebal, Seberang Perai Selatan, P. Pinang, Malaysia. e-mail: ceashraf@eng.usm.my

Soon Min Ng

School of Civil Engineering, USM, Engineering Campus,  14300 NibongTebal, Seberang Perai Selatan, P. Pinang, Malaysia. e-mail: soonmin1612@hotmail.com

Eng Keat Gey

School of Civil Engineering, USM, Engineering Campus,  14300 NibongTebal, Seberang Perai Selatan, P. Pinang, Malaysia. e-mail: mc_ekeat@hotmail.com

 

 ABSTRACT

The increased development and expansion of population in urbanize area in Malaysia have created a definite need to construct an inter-basin water transfer tunnel to fulfil the increase demand of water in the water scarcity region. As one of the main component in the inter basin raw water transfer tunnel project, the Kelau Dam had been designed to serve as a regulating dam in order to maintain a sufficient water level in the Kelau River for the water intake. The successful construction and operation of the dam over the full range of loading require a comprehensive evaluation of the dam designed before the construction proceeds. Thus, this study serves to investigate the factors that can cause instability of the earth-fill dam slope and to evaluate the earth-fill dam performance under main critical conditions by determining the factor of safety (FOS) of the dam conceptual design. Four main critical conditions considered in the analysis are end of construction, steady state, steady state with seismic loading and rapid drawdown conditions. This study began with detailed site characterization and investigation for the engineering information needed in the slope stability analysis. The dam slope stability analysis considering of the critical conditions were carried out using limit equilibrium method (LEM), shear strength reduction method together with seepage analysis using finite element method (FEM). It is found that FOS of rapid drawdown and steady state with seismic loading conditions are close to each other and have obvious lower value compare to steady state and end of construction conditions. The 2-D conceptual model of the earth-fill dam can be classified as stable under all critical loadings as the FOS are more than the minimum requirement specified by the design. Factors of safety computed by both LEM and FEM are close to each other where differences in percentage are less than 6 %. Based on the seepage qualitative and quantitative results analysis, piping failure at the toe of downstream slope is unlikely to occur due to systematic arrangement of filters and drains at internal surface of slope.

Keywords: Earth-fill dam, slope stability, limit equilibrium method, finite element method, factor of safety, end of construction, steady state, steady state with seismic loading, rapid drawdown.

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