With a duty to maintain the existing water infrastructure, and expand capacity for the future, Thames Water engaged The Trenchless Experts, Terra Solutions to upgrade the Waste Water Treatment Plant in Wokingham. Serving 11,000 people daily, this plant was in need of modernisation. Terra Solutions were contracted to install- through Guided Auger Boring– a 500mmø vitrified clay jacking pipe to connect the newly created inlet chamber to the existing Dry Well.
The job did provide a number of unique challenges, largely stemming from the age of the waste water treatment plant. With pipework as old as this there is often a risk of coming into contact with asbestos. With such antiquity, there were miscellaneous materials present in the earth that could not be accounted for through borehole exploration, which provided a few surprises as the job progressed.
The inlet chamber as constructed by Terra Solutions was to be used as the launch shaft for this drive. Working in such a confined space, Terra solutions took all necessary precautions to ensure the safety of our staff. Equipment such as gas monitors and fall arresters were in place, and the team had thoroughly rehearsed the evacuation drill and were all certified to be able to work in confined spaces.
It was necessary to construct a platform at the bottom of the pit from sleepers to raise the rig 575mm to the centre line of the bore. These sleepers were lowered into the shaft by 5T crane. With this in place the guidance system could be assembled and a theodolite setup performed. This was verified by the site manager before Terra began to bore.
The ground conditions indicated firm London Clay with little water and no rock.
At the reception end, in the Dry Well, an opening 700mm x 700mm was created to receive the pilot rods and casings. As the casings progressed spoil was expelled into the drive shaft & removed periodically by the attending excavator.
The heavy pilot rods and heavy casings were winched from the below ground chamber of the Dry Well building using a gantry with electric winch up to ground level. These were then rolled out to be removed by a digger.
The auger drive adaptor was subsequently removed and a pipe thrust adaptor installed in front of the thrust plate and secured. The product pipe was then continually added until it reached the reception shaft within the Dry Well.
The 500mmø pipe connecting the Inlet chamber to the existing Dry Well was installed successfully, allowing work to progress to the construction of a new Wet Well. This job was typical of the high degree of accuracy provided by the Guided Auger Boring technique, which maintains Terra Solutions’ reputation as The Trenchless Experts.