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Sri Lanka - Waste Water Project of Messrs. Angerlehner



8. November 2010

The Water and Sewerage Project undertaken by Messrs. Angerlehner for the Ministry of Water Supply and Drainage of the Government of Sri Lanka is about to be completed after a period of three years  

Scope of work included construction of pumping station Wellawatte, which is used for disposal of sewage in the Southern Catchment of Greater Colombo, on the one hand and the rehabilitation of a significant part of the sewerage system of the Southern Catchment of Greater Colombo, which transports wastewater to the pumping station, on the other hand. Due to the bad condition of the over 100 years old pipes, inhabitants were constantly confronted with flooding or collapse of the sewers and pollution of ground and drinking water.In late 2007 preliminary works for sewer rehabilitation started. Using a high pressure cleaning vehicle (removal of sediments and incrustations) the sewer was first cleaned, then the cracks and damages were documented using CCTV in order to develop a rehabilitation concept.

Cured-in-place pipe (CIPP) was chosen as the trenchless sewer rehabilitation method. Mobile production provides a fast, efficient and long lasting rehabilitation. Remarkable is the minimal reduction of cross section as well as favourable hydraulic features, which raise flow capacity. Inlets were re-opened properly and manholes were rehabilitated on the several kilometer long rehabilitation distance. Dimensions ranged from circular profile DN 300 – 450 mm and egg shaped profile 500/700 to 750/1050 mm. Impregnation of liner with resin was undertaken at the storage depot in specialized containers. The team impregnated up to 240 meter of liner per day. Due to high temperatures, liners were stored on ice for transportation. Im some stretches rehabilitaiton had to take place during the night or rehabilitation distances had to be expanded from 200 to 300 meters due to high traffic loads. In early 2008 the project team started with planning and geotechnical studies for the construction works in the area of Wellawatte pumping station.

Works comprised the following main components: construction of the new pumping station with a capacity of 300l/s, supply and installation of four dry submersible pump sets, construction of a new coarse screen, a fine screen set and a grit removal facility and supply and installation of all mechanical & electrical equipment including SCADA system for the pumping station.The shortage of access and space at the construction site, as well as the adverse soil conditions and several adjacent buildings closely located, sometimes less than 1m distance to the construction pit posed engineering and technical challenges.