A 16M Deep Basement Excavation in Kuala Lumpur Karst: Mixed Retention Solution-Paper

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The paper presents a 16 m-deep basement excavation in Kuala Lumpur’s highly variable karst limestone, where rock-head depths ranged roughly from 6 to 19 m and groundwater was shallow. The 5,700 m² development required excavation around a 275 m perimeter.<br /><br />Instead of the tendered soldier-pile and timber-lagging system, the project used a mixed retention solution tailored to local ground conditions. Deep soil mixing (DSM) formed a gravity wall along the West side, where rock was relatively shallow and consistent. Contiguous bored piles (CBPs), supported by removable ground anchors, were used elsewhere, including areas with deeper or more irregular rock and limited working space. Jet-mixed columns sealed gaps between piles, while curtain and base grouting addressed water seepage through fractured limestone. Detailed rock probing was essential to map the karst profile and select appropriate wall types and pile sockets.<br /><br />Construction and excavation proceeded without major groundwater inflow or strut-related obstructions. DSM samples exceeded the specified minimum strength. Some localized challenges—including organic peaty soil, blasting near the DSM wall, and over-excavated rock benches—were addressed using replacement mixed columns, vibration monitoring, and additional anchors.<br /><br />Monitoring showed satisfactory performance. The DSM wall moved only about 1 mm, compared with approximately 8 mm predicted. CBP movements ranged from 3 to 20 mm and were generally within or better than predictions; additional anchors were installed where movement exceeded expectations. Ground settlement was mostly limited, with one localized instance linked to removal of support behind a kerb wall.<br /><br />The case demonstrates that combining retention methods can provide a cost- and time-effective alternative to conventional systems in karst terrain. Success depended on thorough probing, close construction supervision, monitoring, and adapting the design when actual conditions differed from expectations.

Keywords

basement excavation

karst limestone

Kuala Lumpur

deep soil mixing

contiguous bored piles

ground anchors

groundwater seepage

rock probing

retention system

ground monitoring