The challenge
The new final effluent pumping station, located mainly below ground in the north-eastern section of the existing Crossness STW, will help to discharge final effluent from the plant during high river levels, when it would otherwise be tide locked. By piping the effluent underneath the river, the new pumping station will allow for a full range of potential flows, from minimum Dry Weather Flow (DWF) up to 12.94m3 per second. To allow this work to begin, a groundworks support solution was required to enable subcontractor, MAL Contractors, to safely carry out its part of the works.
Chandra Kahendran, Project Manager at MAL Contractors, spoke on their involvement on this project, saying: “We were contracted to carry out the construction of the new pumping station, at which time Mabey Hire’s temporary works package had been specified by the principal contractor. We picked up the temporary groundworks designs directly with the Mabey Hire team, looking to align the proposed scheme with our own planned construction sequence, enabling us to get a better idea of how we could complete our works.”
Our solution
Due to the depth of excavation required, it was imperative that the solutions we provided could provide a safe working site for the MAL Contractors team. It was for this reason that our larger capacity bracing equipment, Super Bracing Strut (SBS) and Supershaft Plus were specified, as Chandra explains: “With the majority of the pumping station structure being underground, we required a range of groundworks support solutions that would be able to safely support the weight of the ground material, and Mabey Hire’s offering did just that. We utilised four of its SBS 600 range of struts to form part of the support structure below ground, as well as a range of the Supershaft bracing in the top section of the works, ensuring the safety of all of our onsite workers.
“Mabey Hire designed and supplied all of the equipment, which we then installed onsite. It was very straightforward to work with, and thanks to the early engagement with the principal contractor there was a seamless transition to hand work over to ourselves.”
Despite all the planning undertaken before works began on site, there were still areas which needed to be addressed as the project progressed. Chandra explained: “When we mobilised to site and began the installation of the steel frames, we found that the sheet pile which had previously been installed by other contractors was out of alignment. Mabey Hire was quick to redesign its trench wall to factor in the additional welds needed to accommodate this, as well as resolving an installation issue we had with one of the beams, which couldn’t be hooked onto the sheet pile. This was all promptly redesigned, and an 18-metre-long beam was supplied to compensate, helping us to swiftly overcome this issue.”
Chandra concluded by saying: “We have found the support that Mabey Hire offer to be extremely helpful, with any issues resolved in a timely and effective manner. This has helped us to coordinate our contracted works with minimal delay and, most importantly, keep our onsite workers safe whilst carrying out construction of the new station.”
