Real-time monitoring and assessment of groundwater responses due to dewatering of an abandoned 7 m deep excavation pit in Kuching City

Abstract

An existing, fully-submerged 7m deep excavation site in Kuching City is to be dewatered after being abandoned for the last 20 years, to enable the subsequent construction of a 3-level basement for the proposed new 18-storey hotel. The site is surrounded by 3 existing hotel complexes and a busy main road. Extensive manual and real-time geotechnical instrumentation were carried out to monitor the groundwater levels around the site, lateral ground movements, building tilts, ground and building settlements. However, the scope of this paper is limited only to the works related to the measured and back-analyzed transient responses of the surrounding groundwater table during the dewatering process. An improvised real-time data acquisition system that facilitates automatic alerts in the form of SMS messages and emails at specified time intervals is conceptually described. The system was improvised by the university researchers and its industry partners. Finite-element analysis was conducted to back-analyze the responses of the groundwater table. Limit stability analysis is used to assess of stability of the surrounding rock slopes. It was revealed that the groundwater table surrounding the excavation site showed immediate response towards the dewatering process. Besides, land slips were also observed at the rock slope surfaces due to the decreasing factor of safety caused by the dewatering process.