Sewer Connection, Stockport

Despite these works being quite challenging in many different ways, traffic management was quite simple on this one. The two connections to the sewer were made at the back of the site, onto a quieter road, and we were therefore able to use ‘give & take’ traffic management.

However, the road was riddled with services including multiple high voltage electric ducts, large water mains, two gas mains (one of them Medium Pressure) and also two very large decommissioned steel mains, likely to have been gas & water. We also had to contend with lower voltage electric cables & BT ducts.

The surface water connection was done first, this required us to excavate in the pavement and a metre into the carriageway, where connection was made into an existing surface water manhole. The depth of this connection was 2 metres. The excavation was sheeted and a third party core-driller was brought in to core-drill the manhole. The pipework was installed, the excavation backfilled, and the manhole was ‘made good’ inside. 

The foul connection required excavation in the footpath also, and then 4 linear metres into the carriageway in the direction of the existing foul manhole. This manhole was 4.3m deep, and United Utilities (owner of the apparatus) required a soffit-to-soffit connection, as is usual for foul connections in particular. The excavation in the carriageway was extensive and required a large pit excavating 4m wide and across half of the carriageway. Within this excavation was an existing Medium Pressure Gas Main, amongst many other services. The presence of the MP Gas Main required us to consult with the owner of the apparatus, Cadent. We put proposals to Cadent which excluded use of the excavator within 1 metre of the Gas Main. Adjacent to the MP main, we had to hand dig, and then the bulk of the excavating was done with a Vacuum Excavator (Vac-Ex), which is basically a big vacuum the size of a very large lorry, see pictures below.

As the MP Gas Main would be passing through our excavation, and the supporting ground dug out from underneath it, the gas main would need to be supported from above. We put proposals to Cadent which included a 5m long steel beam, 150mm x 100mm, placed directly above the gas main. From the steel beam, we strapped the gas main at 500mm centres. Cadent approved all of our proposals and visited site to inspect our method of working, which was all satisfactory to them. 

The excavation at its deepest was 4.3m, which had to be excavated with the Vac-Ex in stages, with us inserting trench sheets, heavy timbers, and acrows as the excavation got deeper. Ordinarily a ‘trench box’ would be lowered into the ground, but with all the services we had to contend with, the excavation had to be sheeted out around and underneath the services. The deepest part of the excavation was directly under the gas main. 

With all of the trench sheeting complete, a third party core-driller was brought in and the manhole core-drilled. The pipework was installed for the foul from the site to the manhole. The manhole was very small inside, for its depth, such as they used to be, this is likely a Victorian-era manhole. As with any manhole entry though, an operative has to be lowered down on a winch, with gas tests done prior and during entry into the manhole. Should anything happen to the operative whilst down the manhole, he would be winched out as opposed to somebody going down there to rescue him. All of our operatives have confined-space training for this reason, which has to be updated and renewed regularly. We cannot undertake new sewer connections without these accreditations, and of course it’s what is needed to keep everybody safe. 

The deep excavation was filled with primary aggregate, with all excavated material having been removed from site. The excavations for both the surface water and foul sewer connection were reinstated at the same time, and the site cleared of all signage and plant & machinery etc.

This was a challenging sewer connection due to the depth of the foul in particular, and also as a result of the Medium Pressure Gas Main, exactly where we didn’t want it. But as always there is a safe method of carrying out these types of works, no matter what the depth and the difficulties involved.

It was a pleasure to have carried out this work for Fox Construction and JW Clark continue to work with Fox Construction on sites across the UK.