Deep excavations in water-bearing gravels in Cork

Overview

Historically only shallow basements were included in developments in Cork city owing to the underlying layers of soft alluvium and high-permeability glaciofluvial gravels. In recent times several large schemes, with basements up to 10m deep, have been completed.

Initially some background will be given to the geology, ground conditions and history of the Cork city centre area. The design and performance of these deep excavation developments will be summarised. Particular emphasis is placed on the most recently completed basement at Penrose Quay.

Although dewatering by deep well systems is feasible, flow rates can be substantial. Careful consideration needs to be given to the site-specific properties of the glaciofluvial gravels to permit the level of the cut-off to be efficiently chosen, so as to minimize inflows and external groundwater lowering and to mitigate against the possible risk of surface settlements. Some details will be given on the structural waterproofing scheme employed.

External surface settlements have been shown to be surprisingly low in several cases. Lateral wall movements were also low and it seems possible that more efficient designs are possible, especially if the small strain stiffness and dilation properties of the material are taken into account.

^{Image credit: Pro House Demolitions (https://www.prohousedemolitionsbrisbane.com)}