Armagh Southern Regional College

Set to provide over 14,000m² of specialist accommodation for students, the new campus at Armagh SRC has been designed to facilitate world class professional and technical education and training. Felix O’Hare created 200 jobs and up to 25 new apprenticeships during the construction of the new building. The new college building contains a new basement up to 8m deep.

To facilitate construction of the basement Quinn Piling installed a Contiguous Piled Wall using CFA Piles drilled to depths of up to 14m. These were designed to act as a free-standing cantilever wall to support depths of excavation of up to 8m. No temporary propping was used during the construction phase. To enable this to happen an innovative piled retention system was used.

In addition, re-design of piles to maximise their capacity, allowed savings to be made in terms of pile numbers, therefore reducing programme and cost Ground conditions on the site comprise a thin mantle of fill overlying soft to firm becoming stiff and very stiff gravelly Clay at depth.

Piling Scope and Details

The new basement and main building structure required Quinn Piling to undertake the design and installation of a CFA Secant Wall and CFA load bearing piles to support the main structure. The scope of works comprised:

• 750mm dia Contiguous Wall – 129no. piles at 900mm centres, and up to 14m deep
• 750mm dia Buttress piles – 43no. at 2.7m centres and up to 10m deep
• 450mm dia Load Bearing Piles – 364no. with loads up to 850kN and up to 13m deep.

Piles were typically founded into the underlying very stiff gravelly Clay. For the load bearing piles, loads of up to 856kN in compression and 200kN in tension had to be taken. Two preliminary static load tests were carried out (loaded up to 2,140kN) to prove capacity. All piles were integrity tested.

Project Innovation

A particular challenge on the project was to create a retaining structure that could stand unproppped in the short term over its entire height of 8m. An initial design using 600mm diameter piles indicated that lateral deflections of the wall would be excessive. Quinn piling therefore came up with an innovative solution to address this and so save time and money for the main contractor.

The solution comprised changing the wall piles from 600mm to 750mm in diameter and including a series of ‘buttressing’ piles constructed at 2.7m centres immediately behind the contiguous piled wall. These piles were also 750mm diameter and raked at 10 degrees and when combined with the wall piles lateral deflections were kept to within the 15mm required. The contiguous pile wall also had to take compressive loads of up to 550kN per metre run.