Balfour Beatty Utility Solutions Limited
- Main contractor: Balfour Beatty Utility Solutions Limited
- Location of works: Tata Steel (Shotton Steel Works) Zone 4 Deeside Industrial Estate CH5 2NH
- Description of works: In filling cable ducts with Bentonite mix under roads and paths and rivers
- Length of ducts: 4485 linear metres (over 8 visits)
- Volume: 126m3
- Mix: The mix required a thermal resistivity of 1.2 Km/W. (mix design as supplied by Prysmian Group.) To ensure that all material was batched correctly sand, cement and bentonite mixture was pre-blended and supplied in 25 kg bags and 1 ton sacks.
National Grid and Scottish Power Transmissions have come together in a joint venture to build the Western Link, a £1 billion project which will help renewable energy from Scotland to homes and business in Wales and England. Construction of the Western Link is being carried out by a consortium of Siemens and Prysmian.
The mix required a thermal resistivity of 1.2 Km/W. (mix design as supplied by Prysmian Group.) To ensure that all material was batched correctly sand, cement and bentonite mixture was pre blended and supplied in 25 kg bags and 1 ton sacks.
How the project was completed
Most of the cables were laid on sand then covered, however at certain locations the Contractor had to have directional drill rigs in to bore under roads, paths and rivers. Once the bore was completed a duct was inserted, then the electric cables were pulled through. Bentonite (Manufacturing & Supply) Limited were tasked to infill all the ducts with a sand, cement bentonite slurry.
Bentonite (Manufacturing & Supply) Ltd supplied two different machines to manufacture and pump the material. Prior to infill the cable ducts were wrapped with Densoseal 16A (as required in the specification) a 25 mm MDPE pipeline was inserted in to both ends for an injection and vent, then the ducts were filled at each end with a rapid hardening material to prevent leakage when being in filled. Our grout master pump was connected to the injection pipeline.
The sand, cement and bentonite dry mixture was mixed with pre weighed pre-blended 25 kg plastic bags in to the mixing tank which held 200 litres of material. Once thoroughly mixed it was pumped out via 25 mm ID rubber hoses which were connected to the MDPE injection line.
When the material started to ooze from the breather end (which was caught in a 25 litre container so not to contaminate the ground) the pumping was stopped and the breather hose was doubled over and held with plastic ties. The pump line was then removed from the injection line and reconnected to another duct which requires infilling.
Our 1 m3 mixer was filled with a 1 ton bag of blended material when mixed it was discharged in to the rear of a concrete lorry, once 4 m3 had been batched the truckmixer was driven to the location where the ducts required infilling.
A SP11 grout pump was attached to the injection pipeline of the duct via a 25 mm MDPE connection. Once all was ready the truckmixer discharged in to the hopper of the grout pump and the slurry was pumped in to the duct. Once material was expelled from the vented end (which was caught in a 25 litre container so not to contaminate the ground) the breather hose was doubled over and held with plastic ties. The pump line was removed from the injection line and reconnected to another duct which required infilling.
A grout master for making bentonite sand cement slurry for small volume using 25 kg bags.
A 1 m3 mixer was used to fill a truckmixer which delivered the material across the site at various locations.