Development of Groundwater Level Fluctuation Response System Subjected to Rainfall for Slope Stability Forecasting
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Development of Groundwater Level Fluctuation Response System Subjected to Rainfall for Slope Stability Forecasting Soon Min Ng1*, Mohd Ashraf Mohamad Ismail2 and Ismail Abustan2 1
School of Energy, Geoscience, Infrastructure and Society, Heriot-Watt University Malaysia, Putrajaya, Malaysia. School of Civil Engineering, Universiti Sains Malaysia (USM), Engineering Campus, Pulau Pinang, Malaysia. E-mail: [email protected]* ; [email protected] ; [email protected] 2
ABSTRACT The rise of groundwater level in slope due to intense rainfall is one of the factors that can trigger slope failure. The groundwater level rise causes increase in the pore water pressure thus reducing the shear resistance of the soil. The purpose of this study is to present a groundwater level evaluation system in response to daily rainfall for slope stability forecasting. The system consists of three important components namely the conceptual multi tank model, unsaturated-saturated seepage flow analysis and stability analysis. The conceptual multi tank model was initially used to determine the fluctuations of groundwater level followed by the unsaturatedsaturated seepage flow analysis to determine the pore water pressure distribution in the slope. Finally, the variation in factor of safety for the slope was determined by stability analysis corresponding to the seepage flow results. The performance of the evaluation system was demonstrated using a case study in Putrajaya, Malaysia. From this study, an early warning system can be developed for slope stability which is essential for disaster prevention during rainfall. INTRODUCTION It is well recognized that heavy rainfall often triggers slope failure and causes significant damage to the local area (Zhang et al., 2011). The tropical climate in Malaysia that experience Southwest monsoon from May to September and northeast monsoon from November to March contribute to the abundant rainfall annually. Therefore, it is not uncommon for steep soil slopes to remain stable for a long period, whereas some gentle slopes may fail after several heavy rainfalls (Li et al., 2005). The rainfall infiltration with the subsequent rise of groundwater table will increase the pore water pressure of the slope (Ng and Shi, 1998). This will increase the weight of the soil mass until a point when the shear strength is unable to resist the additional driving force thus triggering slope failure. Hence, the groundwater level and pore water pressure distribution provides an important information regarding the stability condition of a slope. Stability analysis is normally carried out to determine the stability state of a slope. Two steps that are basically involved in stability analysis are computing the factor of safety (FOS) for the potential slip surfaces and identifying the critical slip surface associated to the minimum FOS (Li et al., 2009). In order to obtain an accurate FOS, input parameters such as the sub-surface profiling, shear strength parameters and groundwater level need to be represented in the field condition. In
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