Underground stations excavation of up to 45m deep for mass rapid transit in limestone formation, Malaysia

Abstract

Kuala Lumpur Limestone formation exhibits karstic features with irregular bedrock profiles and variable weathering condition. The Klang Valley Mass Rapid Transit (KVMRT) SBK Line project is the first Mass Rapid Transit project in Malaysia. There are three underground stations namely Tun Razak Exchange (TRX) station, Cochrane Station and Maluri Station located in Kuala Lumpur limestone formation. TRX Station is the deepest station with maximum excavation depth of 45m below ground and also one of the underground interchange stations for future line. Cochrane Station with maximum excavation depth of 32m below ground also serves as launching shaft for the tunnel boring machine from both ends of the station. Maluri Station with maximum excavation depth of 20m below ground includes an underground train crossover as operational requirement. A technically appropriate and cost effective temporary earth retaining system suitable for the challenging geological formation using secant pile wall supported by temporary ground anchors or temporary strutting was adopted. High ground water table is also a challenge for the deep excavation. Rock grouting was carried out to prevent water ingress through rock fissures and cavities into the excavation pit as well as to prevent excessive ground settlement and occurrences of sinkholes surrounding the excavation area due to groundwater drawdown. Vertical rock excavation adjacent to the retaining wall involving rock slope strengthening works, surface protection, controlled blasting and vibration control was successfully designed and implemented. Temporary traffic decking on top of underground station was designed in order to maintain the traffic flow during the station excavation works. This paper presents the design of the temporary earth retaining system together with vertical rock excavation to the final depth of the station in karstic limestone formation. The unique experience (design and construction) gained from this project will be useful reference for similar excavation works, especially in mature karstic limestone formation.