Rehabilitation of trunk sewers in Tuen Mun, Hong Kong

The Drainage Services Department of the Government of the Hong Kong Special Administrative Region places great emphasis on maintaining a reliable sewage collection system in Hong Kong. The existing trunk sewer (concrete box culvert) in Tuen Mun district, serving a population of over 480 000, has seriously deteriorated and there was an imminent need for rehabilitation as the consequences of its structural failure, such as road collapse and sewage overflow, would be catastrophic. The rehabilitation was required to be executed under a live high and rapid sewage flow condition. After de-silting, glass-fibre-reinforced plastic (GRP) circular segments were inserted into the box culvert through temporary working pits to form a fully structural liner. To ascertain the inherent curvature of the box culvert, three-dimensional laser scanning was carried out so that tailor-made GRP segments could be determined for the curved locations. Besides other site constraints, upkeeping the top site safety standard was of upmost importance. Poisonous and explosive gases are commonly found in sewage. To minimise worker-entry operations, tailor-made robotic machines were developed to take up parts of the de-silting tasks and installation of liners. Moreover, enhanced protection systems were devised against the threat of the Covid-19 pandemic during construction.