Introduction
An intricate cofferdam solution provided by Groundforce, proved to be the backbone for safety and the success of a sensitive water scheme for Irish Water. The new intake works on the River Clodiagh are part of Phase 1 of the Thurles Regional Water Supply Scheme for Irish Water and replaces existing water supply sources that are vulnerable to contamination.
The aim of the project was to construct a new intake structure and an underground holding tank and pumping station with associated pipework, power supply and service ducting on the River Clodiagh near Holycross, County Tipperary. As the site was located in a Special Area of Conservation with an unusually high numbers of otters, crayfish, lamprey and badgers living in the river and in the surrounding fields and woodland, pollution control and habitat preservation were paramount.
The Project
Given the poor ground conditions, 50no. 15m long precast concrete piles were required to support the proposed concrete structures and interconnecting pipe work. Despite the poor silty ground conditions and high water table, a safe and dry working area was ensured through three interlinked cofferdams using 7m long Larsen L603 sheet piles for the intake chamber and gravity main and 11m long Larsen L605 sheet piles for the pump house.
Solution
To provide suitable support for these cofferdams, Groundforce supplied heavy duty hydraulic frames, egabrace, and HSK150 hydraulic props installed as kneebraces across the corners. For the intake chamber and pump house, three levels of Megabrace and eight knee-braces were required. An additional two levels of Megabrace and four MP80 props supported the excavation linking the intake chamber and the pump house, to facilitate the installation of the connecting pipe-work. Furthermore, edge protection, ladder access solutions and pile ropping equipment for the precast piles were also supplied by Groundforce. The cofferdam solution fully satisfied the design brief since it coped perfectly with the main concern of ensuring a safe working area while protecting the environment on what was a very confined site.
The high water table was factored into the design of the shoring system with water ingress minimised to such an extent that is was much easier to de-water than anticipated. There was complete confidence in the safe access provided to the excavations themselves due to the strength of the system. And as the sheet-piles were kept in place for approximately three months it was crucial that workers could confidently work within these underground work-zones productively and safely.
comments Eoin Delaney, MEIC Project Manager.