2024
London
Imperial College London is developing its campus at White City, 23-acres located on Wood Lane, London. The enabling works package, currently under delivery by Careys as principal contractor, includes a new bridge over the adjacent LUL Central Line and a buried basement that will eventually be part of a subterranean road network serving basements to be constructed in future phases. Operating alongside the designer, Waterman Structures, the Careys team needed a total solution that could work for Imperial.
The works included a concrete basement box with secant pile walls, which required a medium level of gas protection alongside waterproofing the space. In addition to this, the project included construction of a new bridge over the Central line in London.
"Early technical liaison with Sika and Careys identified and resolved difficult interfaces in a holistic manner that led to practical, integrated solutions for the protection of the buried structures against gas and water ingress, in difficult ground conditions. The collaborative approach to design avoided prolonged discussions and unnecessary, complex or compromised details that would be difficult to install, helping all parties to contribute to the reduction of the associated risks. Thank you to everyone involved." Marcello Marinoni, Regional Director - Waterman Structures
Project Requirements
The Imperial construction site was very tight in terms of manoeuvrability. Within a live campus and surrounded by main roads, and a railway line, its layout needed to be taken into consideration with thorough planning for any on-site work.
Early-stage detailing with Waterman Structures was especially important too, the key challenge being the need to ensure the continuity of gas-proofing to the basement, in addition to waterproofing below the water table to achieve Grade 2 to BS8102 2022, considering all construction phases.
Sika Solutions
Careys, utilised a combination of Sika waterproofing products to fulfil this project with concrete provided by Capital Concrete. This included SikaProof® A+ 08, Sika® Watertight Concrete, Sikalastic®-8800, and Sikalastic®-851.
Firstly, 2,500 m2 of SikaProof® A+ 08 was selected as the product could effectively act as both a gas proof and watertight membrane for the concrete basement box. An FPO sheet membrane for fully bonded below ground waterproofing, SikaProof® A+ 08 is designed for reinforced concrete structures and can be pre- or post-applied.
Offering fast and easy installation, a special hybrid bonding layer on the membrane forms a full and permanent dual bond with the concrete structure. Joints are sealed with cold-applied tapes and the product offers high flexibility and crack-bridging capabilities along with high resistance to significant water pressure.
1,000 m3 of Sika® Watertight Concrete — now the most widely used system of its type in the UK — was selected for the liner walls, capping beam and basement slab due to the speed and the ease of construction it could offer the location. Alongside this, 1,000 m2 of Sikalastic®-8800 and 1,000 m2 of Sikalastic®-851 was chosen again due to the speed of application and quality level of both products.
Products Used
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Sikalastic®-8800 was used for the podium slab above the basement which was all completely buried. Sikalastic®-8800 is a 2- part, pure polyurea, hot spray applied, waterproofing and protection membrane which is fast-curing. The fast-curing element of this product allows an almost immediate return-to-service time, and the spray application offers fast coverage of the substrate. Both factors were appealing for the project, allowing minimal delay.
Sikalastic®-851 is a liquid applied polyurethane/polyurea hybrid membrane which was required to be used on elements in conjunction with London Underground and Highways, such as the new bridge crossing, because it has received approval from the Highways Authority Product Approval Scheme (HAPAS). HAPAS approved products provide certified assurance for local authorities and contractors for highway repair projects.
In addition to the seamless collaboration between Sika and Careys in ensuring quality product supply and installation, Sika provided free on-site support and guidance throughout the project. This included toolbox talks and waterproofing installation assessments, to ensure project success.
"This has been another great example of collaboration between Sika and Careys. The aligned attitudes towards quality between the two companies always results in a great outcome and robust design." James Clarke, Specification Manager - Sika
"Sika helped us deliver a robust waterproofing solution with seamless installation, providing guidance and training as the installation progressed. This was helped by the simple installation of their products, which did not require complex or difficult processes." Andrew Sadler, Senior Engineer - Careys