CONSTRUCTION OF THE MARINA BARRAGE
(PROJECT BRIEF)
(JAN 2005 - DEC 2007)

Before (Feb 2005)

Revised Plan (Jun 2008)

Actual (August 2008)

Actual (July 2008)

The Straits Times, Thursday, July 10 2008
A construction worker checking out the completed $226 million Marina Barrage, a dam built across the Marina Channel to create a freshwater reservoir. Singapore's first urban freshwater reservoir – at 10,000ha, or one-sixth of Singapore – will provide desalinated water to meet the country's growing demand. The barrage will also serve as a flood-control gate and a tourist attraction.
The new reservoir – together with supplies from imported water, Newater and desalinated water – will help Singapore become self-sufficient in water by 2061, when its water agreements with Malaysia end. Singapore currently consumes 1.36 billion litres of water a day, equivalent to 500 Olympic-size swimming pools.

Actual (August 2008)

The Straits Times, Monday, August 25 2008
Some 25,000 people ran across the Marina Barrage at part of a half marathon of 21km yesterday. It was the first time the 300m-long barrage - a dam built across the Marina Channel to form Marina Reservoir - has been included in the Safra Singapore Bay Run and Army Half Marathon.

Reported from Zaobao, this was the first event since the completion of the Barrage. The Marina Barrage will be open to the public in November.

TECHNICAL VISIT TO THE MARINA BARRAGE ORGANISED BY THE INSTITUTION OF ENGINEERS, SINGAPORE (27 FEB 2009)

Barrage view from Pump House to the East Abutment

Drainage Pump House. View from the Barrage.

Drainage Pump House. View from the main entrance.

INTRODUCTION
The Marina Barrage is part of a comprehensive flood control scheme to alleviate existing flooding in the low-lying areas of the city. With the Barrage and other flood-alleviation projects, flood-prone areas in Singapore will be further reduced from the current 150 ha to 85 ha, down from 3200 ha in the 1970s.

The Marina Barrage will enhance Singapore's water supply in line with Singapore's Four National Taps water supply strategy to diversify its water sources (The 4 National Taps are: local catchment, reclaimed water, desalted water and imported water). The Marina Reservoir will have the largest urban catchment of 10,000 ha among all the reservoirs. With this Project, about 60 per cent of Singapore will become catchment area.

The Project is unique in that it is designed to achieve three aims: to act as a tidal barrier for flood control, to create a new reservoir to augment the water supply and to maintain a new body of freshwater at constant level in the heart of the city as a major lifestyle attraction. The aesthetically pleasing water body that is not subjected to tidal variations provides a new recreational place for sports on the water.

When the Marina Barrage project is completed by the end of 2007, it will be a prominent landmark in Marina South. The Project has been carefully designed to blend in well with the environment, with guidance from Urban Redevelopment Authority (URA)'s Design Advisory Panel.

HOW DOES THE BARRAGE WORK?
The barrage, which comprises nine numbers of 26.8-metre-long hydraulically operated steel crest gates, will be built across the 350m wide Marina Channel to keep out sea water. Under normal conditions, the steel gates will remain closed to isolate the reservoir from the sea. During heavy rain, the steel gates will open as necessary to release excess stormwater to the sea when the tide is low. However, when it is not possible to do so during high tide, the Drainage Pumping Station capable of pumping up to 280 cubic metres per second will pump out the excess stormwater into the sea.

COMPOSITION OF THE PROJECT
The Project comprises:
1) Marina South Area
- 2-storey drainage pumping station + Visitor’s centre (one block)
- Electrical building and underground fuel tank
- Green roof mound, water future and landscape
2) Barrage
- Channel width: about 350m
- 9 piers with spacing 33.75m
- 9 nos of hydraulically operated steel crest gate with each size 26.75m wide and 5m high, weighing about 90-ton
- Pedestrian bridge
3) East Abutment
- Boat hoist
- Access ramp
4) Dredging and beach restoration

LOCATION OF THE PROJECT
Across marina channel at marina south

ARCHITECTURAL FEATURES
- Helix ramp to mount the greenery roof covering the Drainage Pump Station (DPS) and Electrical Building;
- "Bullnose" concrete capping to outline the Barrage, DPS, Electrical Building and Helix Ramp;
- Aluminium curtain wall and claddings;
- Glass canopy, feature wall, water features

FACTS OF THE CONTRACT
- Contract Value: S$226 million
- Client: Public Utilities Board (PUB)
- Consultant cum SO: Camp Dresser & Mckee Int. (S) Pte Ltd (CDM)
- AC Checker to CDM: KKT Consultant
- Conditions of Contract: Public works of condition of contract with particular specification subject to measurement on completion. Design and build according to the Contractor’s proposals for the Barrage and interface areas. Build only for DPS, visitor’s center, electrical building and other facilities.
- Main Contractor: Koh Brothers Building & Civil Engineering Contractor (Pte.) Ltd
- Contractor's Permanent Work Designer: Black & Veatch (Sea) Pte Ltd
- Contractor's Temporary Work Designer: AGS Consult Civil and Geotechnical Engineers
- Commencement of the Contract: 03 Jan 05
- Contract Completion: 02 Jan 08
- Contract Duration: 36 months (3 years)
- Channel to Remain Navigation: Minimum 100m clearance until 31 March 2006

CONSTRUCTION CHALLENGE
The site has two layers of Marine Clay, namely, Upper Marine Clay (~10m thick) and Lower Marine Clay (~20m thick) spreading over below the fill layer (~10m thick) of the ground level. The Old Alluvium is generally below 40-50m below. The temporary double skin sheet pile wall scheme is adopted to form the marine cofferdam to retain about 11m high hydrostatic and wave pressure to provide a dry working area within it. Before installation of the marine sheet piles, the Upper Marine Clay is to be dredged and filled with sand to create sandkey along marine cofferdam to obtain adequate passive resistance. The 12m wide marine cofferdam must be robust enough to be self-supported gravity structure. This is achieved by using two paralleled rows of sheet pile walls with filled sand. The sheet pile is FSP IV, 42m depth and the cofferdam is filled with sand with 2 rows of tie rods on top to form a gravity wall in the sea . Well-point dewatering inside the cofferdam is followed and sand berm on the dry side (working area) is to balance the hydrostatic and wave pressure from sea side. The subsequent permanent work construction will be carried out after the cofferdam is enclosed. Total tonnage of the sheet pile is approximately 17,000. The design involves the contractor’s PE and specialist checker, and PUB’s geotechnical advisor. The process calls for the interpretation and selection of the appropriate soil parameters from historical and additional on-site soil investigation. Adequate instrumentation is installed and weekly monitoring being carried out during construction.

Driving the marine sheet piles to the designed 42m deep is never easy. The Contractor has experienced the initial hard time of experimenting different types of vibro hammers and piling sequence to gradually pick up the speed of the schedule.

Sandfilling from barge into the completed double wall sheet piles is another issue. The filling shall be gradually and evenly distributed so that the pressure to the both side of sheet pile wall is balanced. Otherwise, the sheet piles would move inward due to one-sided local pressure. Also, the residual marine silt trapped underneath the sheet piles shall be totally cleared. The remedial measure for the tilted marine sheet piles is to dump rocks to the side of sheet pile wall to maintain the balance.

Due to the upper marine clay underlaid the excavated area, when DPS initial excavation to the formation level (from ground RL103 to pilecap RL91), the progressive movement recorded by the inclinometer indicated the soil movement. The record was beyond the alert level. The affected nearby ground sank by about 800mm. These indicated that the shear failure curve was formed along the upper marine clay. The excavation had to be stopped and immediately backfilled to the RL97 to stable the soil. The locally braced excavation with sheet piles and strutting and the segmental construction method were introduced. The method is to excavate and cast the base slab block by block (about 10m x 10m) and in non-continuous pattern so that the soil disturbance is kept to the minimum. This method though dramatically reduces the site progress.

Overall, the construction progress is largely determined by the cofferdam design and the segmental construction sequence.

Leakage test to the crest gate and stop log undergoes the learning and some trial-and-error process. In the end, with cofferdam and add-on temporary dams to separate East Abutment and Barrage, by using stop logs and locally pumping in water to test the leakage rate of the stop log and crest gate, two sets of stop logs at one time, the testing is managed complete.

Underground seepage or piping beneath permanent structure (energy dissipating basin) at the completed east part of barrage (first stage of completed barrage) is another issue raised by the temporary works PE (professional engineer). It was observed that the underground water was gushing out from the king post embedded in the completed concrete slab and the narrow gap between the base slab and cofferdam wall, when the enclosed cofferdam was pumped out of water. The phenomenon is interpreted by the temporary works PE as the the seepage or piping, which shall be eliminated.

BRIEF CONSTRUCTION SEQUENCE
- Overall at Drainage Pumping Station (DPS) Side (Marina South):
DPS -> Electrical building -> Dining extension -> Ramp -> Retaining wall, Elliptical pool -> External works. Underground electrical cable routing is to be carried out with construction of dining extension and ramp.

- For Drainage Pumping Station (DPS) and East Abutment (Marina East):
Drive land based sheet piles, Remove exiting rock bund along the cofferdam -> Drive marine sheet piles -> Install waler, tie-rod, backfill with sand inside of the cofferdam, dewatering inside cofferdam -> (when cofferdam is formed to be a gravity wall) Pump out water -> Bulk excavation -> Install bored piles -> Braced excavation and segmental construction for the base slab -> Super structure RC works (for DPS: 2 storey operation and visitor center, walls for pumphouse, discharge channel wall, pump inlet and outlet concrete, pumphouse roof) -> M&E installation, testing, commissioning -> Dismantle cofferdam

- For Barrage:
Dredging and backfilled with sand key -> Install cofferdam (similar to DPS) -> Install bored piles -> RC raft foundation -> RC Piers -> Energy dissipation slab -> Install M&E 2nd cast-in sockets -> Install steel crest gates -> Install hydraulic cylinder, LCP and HPU inside the pier -> M&E testing and commissioning -> Install vessel impact barrier -> Dismantle cofferdam -> Install overhead bridge -> Architectural finishes and rip rap reinstatement

SITE LAYOUT AND LOGISTICS
- Cranage. Due to the nature of the structure (spreading along a strip and 2 storey only), only enough crawler cranes are used. Crawler cranes access are along the top of cofferdam and outside discharge channel wall (DPS).
- Access. Traffic access has several stages: excavation, RC super structure, external works.
- Office, canteen, workers' rest area, M&E storage area.
- Traffic across Marina South (DPS) and Marina East (1st stage of Barrage and East Abutment): by ferry.

CONTRACTOR'S SITE ORGANISATION
Generally, this is the two-layers structure. Senior PM, PM, QS, planning and scheduling, QA/QC and document control, drafters to perform the project control function, and site managers, engineers, foremen, store keeper to perform operation function. Of course, there have statutory required safety officer and supervisors. One of the company's directors is the project director (not station on site) and the HQ's contract manager helps the contractual matters. Total there are about 30 site staff and 300 workers (including sub-contractors' workers).

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