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Delta was asked for advice and guidance on a failed waterproofing system. The existing structure had a 5-level basement which houses: kitchens, food storage and food preparation areas, spa, plant rooms and accommodation. Near to a large river, the site was well within the water table. The original waterproofing system was based on the secant piled walls and a block wall internally to provide a basic drained protection system with drainage holes at various points to drain to various levels.
Over time, the third floor had become completely saturated with all levels of the basement experiencing water ingress in varying levels, from damp patches to significant “jets” of water and flows of water through the secant piles.
Following preliminary site inspections, discussions were held on remedial options, methodology for remedial works and cost. Balancing costs with quality, method suitability testing was carried out on trial areas. A combination of resin injections and curtain injection was proposed prior to the installation of a Type C cavity drain membrane system to facilitate performance levels. Alternative combinations were suggested on two trial areas.
Following trials and analysis of approach, Delta suggested the use of Koster G4 Gel as a curtain injection to areas identified after exposure works to each area, in combination with Koster 2 IN 1 injection resin to the corbel detail. Each area would be injected and monitored for a period of 3 weeks prior to the installation of the Delta Type C cavity drain system. To achieve a full belts and braces approach, further tweaks to the design would be incorporated as and when different degrees of water ingress were encountered or where concrete to the scant piles were particularly poor, this included increasing levels of the G4 salt accelerant to the G4 Gel to increase speed of reaction without compromising the ability to spread to create the “waterproof curtain” behind the piles in the area.
As the entire sub-structure was susceptible to hydrostatic pressure, the best approach to the 5-levels would be to work one level at a time, working downwards in sequence.
The principles of the Type C cavity drain system were straightforward and typical of a multi-level basement. Additional design considerations were incorporated for detailing the corbel on which mid floor slabs required a careful approach. Increasing the number of downward drainage weepholes from upper to lower levels was suggested for continued access for maintenance, along with discharge points.
In addition to this approach, compartmentalisation of the cavity drainage system was required for fire safety.
The timeframe for the remedial works was over a year, with work to levels 2 and 3 having already been completed. The overall strategy, continuous trials, site monitoring and the ability to adapt the overall waterproofing design throughout the project have enabled completion of the works to date to an incredibly high standard with all parties confident with the positive and collaborative approach.
