Northern Ireland: Omagh Hospital Link Road Bridge

DAWSON-WAM was appointed by Whitemountain/Coffey JV to provide all the piling requirements for a new road bridge. The bridge formed part of the Omagh Link Road Project which was set up as an enabling works package to provide a suitable access road prior to the construction of a new hospital.

Technical Information:

DAWSON-WAM worked alongside their geotechnical engineers Byrne Looby Partners to provide the design and all engineering supervision for installation of the following:

• 172nr 525mm diameter load bearing piles socketed 3m into rock (basalt)
• 2nr sheet piled cofferdams to enable the construction of bridge piers. Each consisting of 60 lin/m of Lx25 steel sheet piles 8m long with one level of framing
• Trimming off steel sheet piles on completion of the RC piers to maintain scour protection around the new structures
• 4nr preliminary static load tests (1nr at each of the 4 abutments/piers
• 44nr dynamic tests (11nr at each abutment/pier)
• 100% sonic integrity testing

The project involved the installation of load bearing piles for two bridge abutments and two piers. The abutments were located on the existing banks of the river while the piers where located at the waters edge. As a result the two piers had to be steel sheet piled to provide a water cut off and enable the formation of a piling platform. On completion of the cofferdams the piling rig was able to track into the cofferdam from the landside and install the load bearing piles. Once the cofferdams were piled they were excavated to a depth of 2m prior to the installation of a frame. Once propped the cofferdams were excavated to formation level and the piles broken down ready for the construction of the RC pier.

The original project was designed to use 750mm dia load bearing piles to achieve the required loadings. Through the use of DAWSON-WAM’s Cased Auger Pile System (CAP) and our ability to socket the piles 3m into the underlying basalt we were able to value engineer the design and reduce the pile diameters to 525mm giving us an advantage over our competitors. Each pile was designed to take 150t in compression and 40t in tension.

The project was completed within 6 weeks, 4 weeks ahead of the construction programme, enabling Whitemountain/Coffey to progress the bridge structure much sooner than originally anticipated.