Safe dewatering and re-construction of an abandoned 7m deep basement in the vicinity of existing buildings in Kuching city centre

In urban areas, many existing buildings and infrastructure are built nearby to one another. Activities associated to deep excavation and dewatering will inevitably cause ground movements and settlements which will affect nearby buildings. The performance of a deep excavation in clay has been extensively studied by many researchers over the years. However, not many studies have been done to investigate and observe the performance of a deep excavation in sandy soil or rock. Furthermore, dewatering is controlled in most of the studies and not many field studies required progressive continuously dewater the fully-submerged abandoned excavated pit before the construction commences. A field case study has been carried out in the research. An existing, fully-submerged 7 m deep excavated pit with a footprint of approximately 40 m x 40 m located in the heart of Kuching city is to be dewatered after being abandoned for the past 20 years in order to facilitate the construction of a new 18-storey hotel with 3 levels of basement. The site is surrounded by 3 existing hotel complexes (located at East, South and South-West) and a busy main road running parallel with the famous 3-km Kuching waterfront. Besides, the river located at the northern boundary and hill located 35 m away at southern boundary. Once the site has been successfully dewatered, the site will be excavated further for the construction of a new 3 m thick raft foundation. A long-term comprehensive geotechnical instrumentation programme has been set up to investigate the possible effects (i) when the submerged and abandoned excavation pit is dewatered and (ii) after dewatering. The entire monitoring programme comprises 6 nos. of water standpipes, 3 nos. of piezometers (real-time), 3 nos. of inclinometers (1 no. real-time), 4 nos. of tiltmeters (real-time), 20 nos. of ground and 25 nos. of building settlement markers (by precise-level method) and 14 nos. of crackmeters which were used to monitor the water table and pore water pressure, lateral soil movement, building tilting, ground and building settlement, and cracking of the existing buildings, respectively.