Urgently called in to address a critical failure at a project site for Coastal Gaslink. This failure posed a severe risk of flooding and potential collapse of the site, which was located adjacent to a fish-bearing river. The situation required an immediate and effective solution that not only ensured the safety of the work site but also complied with stringent environmental regulations.
The project faced significant challenges from the outset, with the original site survey providing conflicting data on the required depth of the cut. After the initial design (Rev_0) was submitted, an additional 4.25 meters of overburden had to be removed to prepare a 7000mm deep bore pit for the Geonex Drill Machine selected by the contractors.
The proximity of the river created substantial hydrostatic pressure on the surrounding area, particularly since the new construction grade was over 2 meters below the groundwater level. Despite extensive dewatering efforts both inside and outside the pit, the hydrostatic pressure exerted on the shoring system was extreme.
Arch implemented an innovative movable strut system, which had previously been tested under challenging conditions but was now pushed to its limits. This system provided the necessary flexibility and strength to accommodate the dynamic pressures exerted by the groundwater and the nearby river.
As an additional measure, a bentonite “box” was installed beyond the headwall to minimize water intrusion when the auger breached the headwall. This solution was critical in maintaining the integrity of the bore pits and ensuring that the drilling operations could proceed safely. Compliance with both regulatory safety standards and environmental protection laws for Coastal Gaslink was a top priority throughout the project.