ASSESSING THE RAPID DRAWDOWN RISKS ON SLOPE STABILITY

Abstract

This study investigates the slope failure that occurred at a 152.18-acre residential development in Kulim. The unreinforced slope was reported to be deemed stable before its failure in the mid-April 2023. Continuous pumping activity for nearby basement construction had been underway for several weeks prior to the failure. To confirm the causality of drawdown effect, the groundwater level was monitored using two piezometer standpipes. The fieldwork investigation confirmed a significant difference in groundwater levels caused by the dewatering activities. By developing a numerical model using Slope/W software, slope stability analysis was performed to assess the slope performance before and after the failure, analysing the impact of dewatering. The findings revealed a significant reduction in the factor of safety (FOS) from 1.348 to 1.080, not adhering to the Jabatan Kerja Raya (JKR)’s slope specifications of a minimum FOS of 1.3 for unreinforced soil. The findings also confirmed the detrimental effect of rapid drawdown on the strength of the slope. To mitigate the slope failure, gabion walls were proposed as cost-effective alternatives. This remedial measure increased the FOS to 1.612, meeting JKR specifications of a minimum FOS of 1.5 for reinforced soil. The findings highlight the importance of educating on groundwater management to enhance safety and mitigate similar risks in future projects.