Groundforce expertise at work at Festival Park

02 Nov

Groundforce design expertise has contributed to a successful solution on a major water quality improvement scheme in Glasgow. The ground support specialist used its extensive experience to help re-design a cofferdam being built on the south side of the river Clyde in Glasgow. The excavation is part of Scottish Water’s ongoing Unsatisfactory Intermittent Discharge (UID) programme, aimed at cleaning up water discharging into the river Clyde.

As part of the programme, principal contractor George Leslie Ltd is installing a new Combined Sewer Overflow (CSO) chamber at Festival Park. The contractor brought in Groundforce to provide the temporary works during the construction of this underground chamber, and the two companies worked together to develop the most efficient solution. 
The initial site investigation report indicated poor ground conditions, so it was quite challenging to find a workable frame solution to support the excavation. In order to establish a more accurate account of the ground conditions, George Leslie Ltd carried out further site investigation work and supplied this to Groundforce as the basis for the temporary works design proposal.

These initial designs were based on a cofferdam measuring approximately 9.9m long, 7.9m wide and 7m deep, which was intended purely for the CSO chamber. But after discussing the methodology in more detail with Groundforce, the contractor proposed increasing the length of the cofferdam to incorporate associated manholes and pipework within the same excavation. As a result, the overall dimensions of the excavation increased to 26m long, 7m wide and 7m deep.

This increase in the length of the cofferdam brought an existing brick retaining wall within the zone of influence of the excavation. Groundforce engineers proposed a method of modelling the surcharge on this wall, which was incorporated in the contractor’s analysis and approved by the project’s designer. This design solution also had to facilitate installation of continues, helical displacement bearing piles within the excavation footprint.

The resulting temporary works solution for this 26m x 7m x 7m CSO chamber cofferdam consists of three levels of Groundforce’s Mega Brace frames propped with two MP125 struts at each level.

In addition to this main cofferdam, Groundforce also provided support for three pipeline excavations and two manhole cofferdams. During the design of the temporary works for these excavations, Groundforce engineering team made various revisions to accommodate clearances for large diameter pipework and for pile locations following close consultation with the George Leslie Ltd site team.

The largest of these cofferdams measured 18.6m long, 3.3m wide and 7m deep. The support solution consisted of a combination of 8m long L605 and L605 Larsen piles; one level of Groundforce’s Mega Brace frame supported by two MP50’s; and two levels of Mega Brace frames supported by three MP50’s. The other cofferdams were also supported with Mega Brace frames, and MP50’s

The remaining smaller cofferdams, which measured 7.1m x 5.7m x 6.5m, were excavated at the same site to accommodate two manholes. Groundforce’s support solution for this excavation consists of three levels of frames made up of Maxi Brace 8R and Maxi Brace 6, with the excavation formed using 8m long Larsen L603 piles. 

George Leslie Ltd began installing the temporary works in February 2016, with the underground structures completed in July 2016.