● Happy Valley Underground Stormwater Storage Scheme

The project comprises the construction of an underground stormwater storage tank with a capacity of 60,000m3, an automatic operation pump station and the Fan Room and associated drains at Happy Valley Recreation Ground. An underground stormwater storage tank is to be built to temporarily store part of the stormwater collected from the upstream catchment through the downstream stormwater drainage systems. The total contract sum is 711 million HKD and the contract period is from September 2012 to April 2018.

W T Chan & Associates Ltd. is appointed by the Contractor to conduct the ELS design for various structures including but not limited to the Still Basin, Box Culvert, and Irrigation Tank. The main constrains that encountered during the design are the high groundwater table, which is only about 0.5m below the existing ground level; and a layer of Clay material at the excavation level. Due to the high groundwater table and clay material being encountered, the embedment length of the sheetpile wall should penetrate beyond the clay layer for the stability of the sheetpile. Moreover, a layer of strut is proposed close to the final excavation level in order to limit the sheetpile wall deflection due to the ‘soft’ clay stratum.