The environmentally led solution involves the use of CFA piling, controlled modulus columns and Trenchmix, to complete the work on two key structures - the resource recovery facility (RRF), and the reuse and recycling centre (RRC).
Bachy Soletanche will construct over 400 CFA piles to support the RRF and the RRC buildings. Once the initial piles for the RRF building have been bored, the team will commence work on constructing a low permeability cut-off wall using the Trenchmix method. This innovative process involves the in-situ mixing of the soil with a cement slurry, which hardens to form a barrier. The cut-off wall, selected as the most efficient method of preventing hydro-static uplift of the ground floor slab, is approximately 400m long, 400mm wide and 6m deep.
Vibro Menard will install approximately 1,130 controlled modulus columns (CMC), providing support for the ground slab of the RFF building. When complete, the solution will allow load-bearing pressures to be distributed between the columns and the soil. The use of CMC, as an alternative to CFA piles, removed the requirement for a fully piled slab, providing savings on materials, cost and programme. In addition, this approach avoids drilling down past an existing sewer, mitigating any risk of service interface.
The use of CMC brings considerable environmental benefits, which include; the elimination of reinforcement cages normally required in CFA piling, a reduction in the thickness of the ground slab saving on concrete and steel, and a reduction in the arisings produced due to CMC being a displacement solution.
Trenchmix further enhances the project's environmental credentials through offering approximately a 30 per cent reduction in the embodied carbon, when compared to the alternative of a traditional sheet piled wall - this saving contributed to an overall reduction across the project of between 10 - 16 per cent. In addition to this, there is a significant reduction for the handling and disposal of arisings from the cut-off wall due to the in-situ mixing rather than a total replacement solution, as well as a reduction in vehicle movements for deliveries and waste disposal.
Commenting on the contract award, UK group managing director, Philip Hines, said: "This project is a great example of where early contractor involvement, with an organisation that can offer the full range of geotechnical solutions, can bring a range of benefits, particularly around sustainable construction. The collaborative approach showcases how we can develop and implement solutions which help contribute towards our target of achieving a 40 per cent reduction in direct CO2 emissions by 2030."
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