TWU Caisson Ring Sewer Connection – Stortford Hertfordshire

Property Management Company
Duration 3 Weeks
Valuation £25k - £75k
Project Overview

SB Civil Engineering were contracted to install  an 8m deep sewer connection for a private developer who needed to connect the two houses that had been built to the main thames water sewer in Hertfordshire. The Thames Water sewer was at this depth as it was at the end of the sewer run at the top of a hill in Bishops Stortford.

We followed a structure of steps which consisted of site setup and permits, excavation, sinking caisson ring shaft, a heading excavation and lastly the sewer pipe installation. To set up the site we used CAT scans and any findings prior to all excavations that could of affected the job were marked out, as was the shaft location. The excavation of the shaft for the sewer connection commenced, once it had been all marked out for the operatives and site supervisor. Various ring sizes of the caisson were installed and as this proceeded the rings  sunk under their own weight. The same process was repeated until the required depth of the shaft to reach the sewer via timber heading was achieved.

A specialist diamond drilling rig was used to cut the required opening (dog kennel) in the face of the caisson ring to enable us to commence with the timber heading tunneling to reach the thames water sewer. A timber frame was installed to form the entrance of the heading (starting frame). On completion of the starting frame being fixed, plumb and true tunneling proceeded by hand. Upon reaching 1m a permanent frame was installed and the side boards and head boards. The new 150mm diameter clay pipe was laid on C30 SR concrete to line and level and the remaining area within the tunnel was filled with concrete hand packed around the pipe.

With the new sewerage connection completed and the back drop manhole installed, SB Civil Engineering left the site with the client relieved to be connected to the main sewer.