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The influent pumping station

Two giant pump shafts and a wet well are being constructed simultaneously by Bombay contractor Hindustan Construction Corporation.

From the 47m diameter, 47m deep wet well the flow of sewage is split via a 5m box section link tunnel to the two pump shafts. Each shaft has a dry, control and pump room at its centre. Sewage is directed in two streams around this to four sumps diametrically opposite the link tunnel. Four pumps in turn lift the sewage to a surge tower and pressurised main, from where it crosses Mahim bay to the Bandra effluent pumping station and outfall tunnel.

After dewatering the abandoned excavations, extensive rock stabilisation on the walls of the three shafts and further excavation was carried out. Concreting started at the beginning of 1998, and by November 17,500m3 had been placed in the pump shafts: work was well advanced on the inner, 19.2m high, 25m diameter walls and outer 52.6m high, 37m diameter walls. 2,400m3 concrete had been placed in the wet well, completing construction of its base.

To reduce heat produced as the large volumes of concrete being poured cure, and to minimise the resultant cracking, BBV has specified a 70% fly ash, 30% portland cement concrete mix.

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