April – June 2019


With increasing demands on the Ilton in Calne, Wessex Water (WW) decided to upgrade the network and employ MDA to install a new storage tank. The first was a 5m ID shaft, 9m deep, sunk using the caisson method.


As a strategic delivery partner for Wessex Water, MDA understood the importance of keeping the existing Sewage Treatment Works (STW) fully operational while our works were being undertaken. In order to do this, we had to plan all deliveries, craneage, concrete pumping and network shutdowns in collaboration with WW.

The 5m ID shaft was excavated so the first ring and concrete jacking collar could be installed. Once the jacking frames were set into the pour, the C32/40 concrete was delivered by local suppliers and pumped into the collar and left to gain strength.

The 5m ID shaft was then constructed using back bolted segments to build the ring on top of the existing ring which provided edge protection and ensured that we were not working over an open excavation. This method was used until the base of the shaft was reached at 9m where the concrete base plug and benching were formed ready to receive the associated pumping system and pipework.

A commendation was received by Wessex Water for MDA being so accommodating and professional while going above and beyond to make sure additional works could be completed without being detrimental to the construction programme.

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