Projects
Stafford Sewer Connections, Case Study
We were approached by Pritpal of Dulkoo Properties, in Stafford, he had built a new house and needed a connection to the sewer, for both foul and surface water.
Objective
Our objective was to make a connection to the surface water connection in the Highway, at 1.5m deep and lay pipework back to the site boundary. The foul connection was a bit trickier at 3.5m deep, and from here we also laid pipework back to the site boundary.
About the project
We met with Stafford Highways to discuss traffic management for the job, and despite the works being on a 3-way junction, we agreed on 2-way traffic lights, but with signage on the side road indicating that traffic on the main road was under signal control. We located the surface water pipe on day 1, on the opposite side of the road to the site. The existing pipe was less than 1.5m deep, and the connection was made using ‘junction insertion’ method. The connection was inspected and passed by Severn Trent Water, and then from the connection point we laid pipework back to the site boundary. The STW Inspector requested that the pipework be concrete-protected, due to how shallow it was in the carriageway. With the surface water pipe laid and the excavation backfilled, we reinstated the Highway to Stafford Highways’ spec. As a Class 1 road, this required in excess of 300mm of tarmac to be laid, in three layers.
The new road surface was allowed to cool overnight, and the traffic lights were switched over in the morning, and excavation was started in preparation for the foul connection. At an invert depth of over 3.5m, we expected to find the top of the 450mm foul sewer at a depth of approx. 3 metres. Due to the depth of the excavation, an extensive amount of trench sheeting and acrow props were required to enable safe entry into the excavation for our operatives. Having excavated down to 2.5m however, and having made the excavation safe, we started to encounter groundwater coming into the sides of the excavation deep down, which were unable to control with pumps. The ground was ‘silty’ and the volume of water made it impossible for us to continue. With the water content we had to deal with and the nature of the ground combined, it is not possible to use pumps to remove the water. We consulted Dewatering Services Ltd whom we have used on a number of occasions, and made plans for them to come to site to ‘dewater’ the ground. Unfortunately they were unable to come there and then, and due to the traffic-sensitive nature of the road, Highways required us to abandon the excavation, reinstate the road and remove the traffic management, which we did.
Just over a week later, we set up the traffic lights all over again….! And Dewatering Services Ltd came to site. In preparation for their arrival, we had re-dug down to a depth of just over two metres, and reinstalled the trench-sheeting system. The Dewatering system included metal rods being pushed 5m into the ground, the whole system was installed in a day. 24 hours later and the excavation had been dried out, we excavated down another metre or so to get to our target depth of 3m, and installed more trench sheets and supports further down. We located the top of the 450mm concrete sewer at 3.15m down from the road level. The concrete sewer was encased in more concrete, which needed to be broken off carefully with a handheld breaker, to gain clear access to the pipe for core-drilling. We instructed a professional core-driller to core-drill into the concrete pipe. With the hole having been cored, we fixed a clay saddle onto the 450mm sewer and secured the saddle and the first clay pipe, with extra-strong and quick-setting mortar. From the connection point we continued to lay 100mm clay pipes towards the boundary. This included excavating under numerous existing services both in the carriageway and in the pavement and cycleway.
The dewatering equipment was removed from site as soon as we came up to 1.5m dig depth, near to the site. The excavation was backfilled and the carriageway, pavement and cycleway all permanently reinstated.
The project was a reasonably challenging one, due to the dig depth and the water content within the ground. But it is not unusual to encounter groundwater such as this, especially at this depth, and we have plenty of expertise in this area, and often at much deeper depths as well. It was a pleasure to have carried out this work for Pritpal, and we wish him every success with this project and any others we are able to help with going forward.
Timeline
Time taken to quote for the works: 1 week
Time taken to obtain Section 106 Licence: Our customer already had this
Time taken to obtain Section 50 Licence: The licence only took a few weeks to obtain….
Leadtime to use S50 Licence: …….but we had to wait in excess of 3 months before the work could be started, due to other works being undertaken in the area, a road closure around the corner. Highways will not often permit two jobs to run concurrently within a certain radius, and we are never able to carry out works in what is a ‘diversion route’ for another road closure.
Time taken to do the work: 3.5 weeks including us having to go away for a week and then come back with Dewatering Services
Total time: 4.5 months including the delay in being able to use our Section 50 licence, due to other roadworks being carried out in the vicinity.
Do you need a sewer connection needs doing? Don’t leave it too late, most people do! Read our article here: How long does it take to do a sewer connection?