Ilijan City, some 100km south of the Manila metropolitan area, is the site of one of WJ Philippines largest projects, where an extensive dewatering system has been installed to aid the construction of a new intake structure of the Batangas Combined Cycle Power Plant.
WJ were engaged by First Balfour to develop and implement a groundwater control strategy for the construction of a new 55m by 45m excavation up to 31m in depth. The initial site investigation information provided to WJ indicated that the excavation would be undertaken through silty sand with gravel. Based on this information it was determined that the most appropriate dewatering method for the excavation would be a perimeter deepwell dewatering system.
Upon mobilising to site it quickly became clear that the ground conditions were different to those anticipated, with the ground more characterised by silty sandy gravels with boulders. Groundwater flow could therefore be considered as more analogous to a rock (where flow is controlled by fissures) as to a soil. This meant that the original groundwater control strategy of deepwells was unlikely to be effective, and that a sump and pump strategy may prove to be more successful.
A system of combined of trenching and sump pumping was therefore installed instead of the deepwells. Despite this change the flows encountered were still very significant, reaching in excess of 2,000l/s at their peak, due to the close proximity of Batangas Bay. To combat these high flows a combination of both electrical submersible sump pumps and diesel centrifugal pumps were utilised.
The sump pits and trenches were located internal to the excavation footprint but external to the actual structures to minimise the disruption to the construction work but to ensure that in the event of any groundwater level rises the system would prove effective.
Another technically challenging project successfully delivered by WJ!
You can learn more about the project here: https://firstbalfour.com/track-record/batangas-combined-cycle-power-plant/
- LOCATION: Ilijan City, Philippines
- CLIENT: First Balfour