See the image below for the detail of 4 no. cable ducts that run from a trench in a raft foundation (on the left) through an approximately 1 m square penetration in the raft foundation, through soil (if it had been backfilled) and through an approx 1 m square penetration in the retaining wall for the basement of an industrial structure. At present there is a continuous flow of water through the base of the penetration in the retaining wall.
My questions are:
- Given that the structure is approximately 50 years old what are the likely original construction details? My theory is that the cable ducts were fed through, the penetration at either end was sealed with mastic but I am unclear if it would have been possible to backfill around the cable ducts or whether the cable ducts are likely in a void filled with ground water?
- What approach could be used to prevent water ingress in through the retaining wall penetration. Is it possible that the existing mastic sealant has degraded with age? Would raking it out and reinstating with a modern product be effective? Is there a system that can be applied on the internal face of the retaining wall that would be effective? Is the best approach leak management to a sump to be pumped out?
- If you were to construct this detail today what approach would you take? My instinct would be to use a puddle flange for each cable duct that was cast into the concrete rather than leaving 1 m square voids to be sealed with mastic. I believe this would have prevented water ingress? What is current best practice for construction these cable duct penetration details?