Lying low to fight storm waters

By Hiranthi Fernando

Incessant rain over the past weeks and reports of floods in certain parts of the country have Colombo residents alarmed. Memories of flood havoc are fresh in their minds. But the problem is receiving attention. Work has started on a new method of laying underground pipes under Phase 2 of the Greater Colombo Flood Control and Environment Improvement Project. Pipes are being laid from the junction of Unity Place and Fifth Lane, across R.A de Mel Mawatha (Duplication Road), Fifth Lane, Galle Road and through Stamboul Place to the sea, with minimum disruption of the surface. The scheme aims to drain the rain water from low-lying areas around Unity Place at Kollupitiya, and discharge it to the sea.

Deputy General Manager, Canal Development and Maintenance of the Sri Lanka Land Reclamation and Development Corporation (SLLRDC) N.V. Gunaratne, says this is the second pipe jacking project in the country.

The first one is in progress under the Beira Sewerage Project of the Water Services and Drainage Board, where sewerage pipes of 1 - 1.5 feet diameter are being pushed through. The Unity Place storm water drainage scheme of the Flood Control Project, is on a larger scale, using massive concrete pipes of 2.5 meter diameter.

Explaining the scheme, Mr. Gunaratne said shafts of varying depths will be excavated at five points along the route of the drain. The first shaft labelled MH 1 will be at the Fifth Lane/27th lane junction. MH 2 is at the Fifth Lane/Duplication Road junction, MH 3 at Galle Road, opposite Fifth Lane, MH 4 at Galle Road opposite Stamboul Place and MH 5 at the bottom of Stamboul Place.

Excavation of the shaft MH 4 on Galle Road began about two weeks ago. Initially the pipes were to pass through Sea Avenue to be let out to the sea. However, the plans were changed since a building at the top of Sea Avenue had a foundation that was not deep and may have been affected by the excavation of the shaft. Mr. Gunaratne said the pipes would pass under the roads and not under any built up areas.

"Before we started, service lines such as water, drainage, and telephones had to be relocated outside the area of work," Mr. Gunaratne explained. "This process has taken an year. Relocation of service lines around the shaft MH 4 is completed and we started work on the shaft. We still have a little more relocation to do around the shaft MH 3. After MH 4 and MH 3 have been excavated, we can start pipe jacking for that section."

"MH 4 and MH 2 are jacking shafts in which the machines will be placed. They are thus larger than the other three shafts which are the receiving shafts, as space is needed to work around the machines. The machine will be placed inside MH 4. The machines are equipped with various pipes for pumping in air and pumping out the mud and water.

According to Mr. Gunaratne the latest method, the Earth Pressure Balancing Seal Method will be used. Sections of concrete pipes will be placed in the machine and pushed through. Before the section is pushed completely into the soil, a collar will be placed so that the next segment of pipe will be secured to it. The earth which collects inside the hollow pipe is kept under pressure and pumped out through the shaft. It comes out in a mud like consistency since there is water at that level.

From the jacking shaft MH 4, pipes will be jacked up to MH 3 and MH 5 at the seaside. From MH 2, pipes will be jacked through up to shafts MH 3 and MH 1. Since the existing ground level at Galle Road is between 8 to 9 metres above Mean Sea Level (MSL), the depth of these two shafts will be greater than the other shafts where the ground level is lower.

The shafts are excavated and the pipes laid so that there is a gradual sloping down to the sea, where the water is let out. For instance, at the first shaft MH1, the depth will be one metre to the top of the pipe, leaving a further 2.5 metres for the pipe and half a metre below the bottom of the pipe. At MH 4, the depth of the shaft is 5.84 metres up to the top level of the pipe, leaving the same depth as in MH 1, for the pipe and allowance below it.

When completed, the drains will be connected to the shafts and the shafts will be covered.

The work is being undertaken by a Japanese company under Japanese funding. The estimated cost is around Rs. 163 million, including the diversion of service lines which is part of the contract. It is scheduled to be completed at the end of year 2000 or by January/February of 2001.

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