Stonbury are immensely proud to be supporting our clients across the UK at such a crucial time and have been designated as 'key workers' by DEFRA and the UK water utility companies. Our teams are working tirelessly to help secure and maintain drinking water supplies, ensuring clean and safe drinking water is provided without interruption to critical services such as our hospitals as well as the general public. Now more than ever, the safety and wellbeing of our staff is of the utmost importance and we have adapted our safe working practices to ensure social distancing precautions are in place and that the correct hygiene practices are being followed. Making safety is our priority, and we endeavour to make sure everyone at Stonbury goes home safe to their family.
The reservoir was made up of two cells, following an extension to the west and north side of the original tank. The walls were cast in situ concrete, which required the passive restraint from the surrounding earth embankment to ensure structural stability, and the roof was finished with precast hollow core concrete planks and a loose lay membrane. This design did not meet the current standard set by the client.
Following a 3D scan of the reservoir, it was decided that a new roof slab would be the best solution, and a scope of works was put into place. During the works, the live cell needed to remain watertight at all times, this was achieved with the use of temporary batten strips, mastic and liquid membrane seals. The joints were regularly inspected and maintained throughout the scheme.
Works began with the removal of the existing overburden, the loose lay membrane and the profiled polystyrene insulation boards. This included hand digging to safely expose the telemetry cables. The roof joints were then filled, the existing membrane on the live side was sealed down and the roof was cleaned in preparation for the new screed.
To form a solid structural foundation, sections of the existing slab were cut into, and the voids were infilled with concrete. This created the base for the support pads, which would support the weight of the new roof. A lightweight screed was then pumped between the pads to profile the roof to a 1 in 100 fall. Once cured, collapsible fill was used to level the surface and protect against the potential effects of ground heave.
Repairs were completed on all of the upstands, including rendering and fillets. However, two of the upstands were in deplorable condition and required breaking out. Overbanding was applied to the remaining upstands, followed by a waterproof liquid membrane. The redundant drainage and pipes were also removed and replaced with a new impermeable drain and new drainage chambers.
Steelwork was lifted onto the roof and tied into place, once secure, concrete was pumped onto the roof in sections and left to cure. To ensure a tight seal between the old and new roof slabs, the void was filled with polystyrene and made watertight using bonded membrane.
To complete the roof, a bitumen primer was applied, followed by a bonded membrane system, which successfully passed a spark test. Following the completion of a flood test, geotextile fleece will be laid, and the overburden will be reinstated.