Introduction
Groundforce’s engineers helped Irish Rail and main contractor SIAC Construction lower the risk of water ingress whilst providing a significant time saving for the client through the use hydraulic props instead of ground anchors at Cork City’s Kent Railway Station extension. The contract involved the construction of a
new entrance building to improve access and provide better links to the city centre. The entrance building has a basement concourse linked via a new subway, to the underpass leading to the existing station building. The common challenge when excavating in Cork City is the presence of highly permeable sands and gravels
which, in conjunction with tidal water conditions, give rise to significant dewatering and excavation support challenges.
The Project
To seal the excavation from penetrating ground water and to ensure a dry working area for the subway a 25m long and 9m wide secant piled perimeter wall was installed in combination with a 4m deep mattress of permeation grout installed 7m below ground level. Due to the limited bearing capacity of the surrounding soil, 22 ground anchors were proposed on the initial temporary works design.
Solution
After carefully evaluating the situation, Groundforce engineers proposed a value engineered internal propping solution using 5 hydraulic props, removing the
need for tie back anchors. This design change resulted in a significant time saving with less finishing work required and quick installation of the props with a 60t
crane and a 21t excavator. For this 14-week Groundforce project, there were significant benefits when compared against the anchors including the advantage of speed of
installation, reduced dewatering and the option of live load monitoring – all contributing towards the successful construction of the basement.
The props provided a significant time saving and resulted in a much lower risk of water ingress where the tie back anchors would have punctured the secant piles.
comments SIAC project manager Adrian Farry.