BAE Systems Initial Enabling Infrastructure Works

RPS provided engineering design and digital delivery services for all major elements of the works for the Govan and Scotstoun yards modifications to accommodate the construction of the new Type 26 frigates on the River Clyde in Glasgow.  

We tendered seven work packages, including a new sheet piled quay wall to facilitate the deepening of a dredge pocket, the removal of a pinch point for the transfer of part ships on land, and new pits both in dry dock and along the quayside berth.  

The main package of works was the replacement of the existing caisson gate with a new flap gate on Dry Dock 2 at Scotstoun. This involved significant civil, mechanical and electrical engineering works within a congested, operational site.

The works were tendered as a Design and Build Contract, awarded to Farrans Construction with RPS as designer in January 2017. 

Challenge

The Scotstoun site is underlain with mudstone, which exhibited some variability during site investigations. Permeability of the mudstone was a primary concern as a path would be available through the material, allowing water into the excavations and undermining the structure.  

In addition, the original dock was constructed in the 1930s in unreinforced concrete, with subsequent modifications undertaken in the late 1970s. The works involved significant demolitions and changes to the existing dock walls, including walls that would act as water-retaining structures when the cofferdam was in place, originally not designed for that purpose. This resulted in significant challenges in maintaining the structural stability of the dock walls during the execution of the works.

Solution

To mitigate the risks inherent in the project, we undertook a detailed analysis of the structure through all stages of the works and prepared a detailed construction sequence that ensured stability at all times.  

The specific measures included:

• Provision of an arched temporary cofferdam
• The installation of ground anchors and temporary secant piled retaining walls, incorporated into the permanent works.
• Significant propping of the existing walls
• Load cells were installed and monitored in real-time on all major structural elements, including hold and monitoring points at critical periods. We correlated monitoring with external water levels at all times.
• We prepared a detailed 3D virtual reality model to visualise and communicate the complicated construction sequence. This was used for health and safety inductions and briefing for all personnel working in excavations and behind temporary cofferdams.
• Specific excavation sequence and onsite supervision of critical operations