Abbey Mills Shaft F Internal Structures consisted of over 6600m3 of reinforced concrete. 3100m3 of that forming the main 1m thick spine walls, 70m in height from pit bottom. The RC H Shaped spine walls consisted of an 8m x 8m central core. All works were carried out in compliance with Confined Space regulations with all access via the 25m diameter shaft at ground level to pit bottom.

Modebest are proud to have won a CONSTRUCT Innovation Award during October 2016 for this project at Abbey Mills, Shaft F, which was the overall winner in the category of Projects over £2.50M that exemplify innovation and people talent in the concrete sector.

Modebest sought many innovative methods to successfully deliver this unique project to comply with the Clients high expectations of “Creating a project that is recognised as world-class for delivery, health and safety, quality, sustainability and community citizenship”. Modebest were subcontracted to MVB under NEC 3 contract as part of the Thames Water Tideway Tunnel.

Slipforming the central core was chosen as the most innovative solution for constructing the 1m thick walls as it offered the following advantages:

• Programme savings over traditional methods
  
• Safer method of construction working in confined spaces
  
• Eliminating construction joints
  
• Maximising craneage output
  
• Integrating strut beams and roof beams into one activity
  

However, the benefits of slipforming the core generated many complex challenges to overcome such as:

• Forming a sloping soffit 10.3m high from the bottom of the pit
  
• Forming 10 no 8m x 4m structural openings
  
• Forming 16 no 7m x 2m structural openings
  

To form the openings we devised a hybrid system utilising the reinforcement in the structure. This was carefully planned using 3D modelling software. The key components involved were as follows:

• GASS props and frames
  
• 12 kilometers of Scaffold tube and fittings
  
• Timber and plywood
  
• Unistrut Channel and threaded bolts
  

Choosing modular components allowed the following project benefits:

• Repeatability - the design principal was repeated for various opening sizes
  
• Sustainability - minimising timber waste
  
• Safe system of work
  
• Improved striking times and process logistics
  

The slipform operation was completed over 27 working days pouring 3100m3 of concrete, fixing 340 tonnes of reinforcement and over 12km of scaffolding to form the openings. To strike the openings, the top platform of the slipform rig was modified to form an enlarged Striking Bin. The advantages of utilising this system were as follows:

• Assembly time saved reusing slipform top platform
  
• Operatives could safely strike the openings from a man rider cage and fill the Striking bin located in the central core
  
• To create an extremely safe system of work, eliminating working at height
  

Another complex challenge on this project was to cast a section of the Level 2 slab 52.5m above the bottom of the pit. Doing so traditionally would involve:

• Erecting 52.5m high falsework from the bottom of the pit
  
• Striking within a confined space
  

The solution was to use innovative reinforced concrete technology. With agreement from MVB and designers Mott McDonald, RC Beams were designed and pre cast on site. MVB were impressed with the occupational health, safety and programme benefits as well as:

• Reinforced concrete technology used to overcome a major Work at Height challenge
  
• 70 man days saved on falsework erection
  
• Programme – Beams installed in 1 day
  
• Economic - 200 man days saved on striking
  
• Removed confined space working
  

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