New Foundation Construction Technology for Sites with the Presence of Marble Cavity
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New foundation construction technologies – Buoyancy Raft Foundation and Shaft-Grouted Barrette have recently been applied by the Housing Department (HD) to overcome the difficulties in design and construction owing to the existence of marble cavity, enabling the multi-storey buildings to be supported by the soil stratum. Formed when the marble is dissolved by the underground water after several hundred thousand of years, marble cavity is common in Hong Kong, such as in Yuen Long, Ma On Shan, and Tung Chung new reclamation area. Marble cavity can only resist very small extra additional loads, large constraints on design and construction will therefore be imposed on the site. |
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 Ground investigation (GI) at the schematic design stage revealed that the site of Wang Fu Court, Yuen Long was underlain by a very large marble cavity with depth around 60 metres from the ground level. The spread of building loads by pile foundation commonly adopted in the industry became not applicable. On the other hand, the rock stratum at some areas was deeper than 175 metres from the ground level, which rendered unreachable by common pile type. After detailed investigation, the project team adopted Building Information Modelling to simulate the geological profile of the site. A three-dimensional print-out produced a geological model of the site to assist the project team to adopt Buoyancy Raft Foundation to support the multi-storey building using soil stratum. |
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Long Ching Estate, Yuen Long is also located at a marble cavity area. The GI revealed that the site was underlain by marble cavity at a relatively deep level below ground. Such situation rendered the spread of building loads by using common pile type not effective. The HD therefore introduced a new pile foundation system called Shaft-Grouted Barrette, in which grouting was carried out around the perimeter of the pile so as to increase the thickness of the soil. As a result, the friction between the pile and the soil for was formed to provide adequate support to taller buildings. |
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