In Leyland, Lancashire, UK, a number of local properties on Moor Road had repeatedly suffered from flooding and United Utilities PLC, the UK Water and Sewerage company responsible for this area, employed Bethell Construction Ltd to design and install a flood alleviation scheme which involved the installation of 370 m of new DN450 concrete sewer down a main residential road in Croston. Moor Road is extremely narrow road and is littered with existing overhead and underground services. The new sewer would outfall at a 12 m diameter settlement tank located in a field at the bottom of the road and with flows then joining the existing sewer system. Bethell Construction, with the ability to design and install efficient and cost effective solutions, opted for a trenchless method due to the previously mentioned restrictions.
The trenchless subcontractor appointed to complete the new sewer installation was Trenchless Solutions Ltd (TSL) of Barnsley, South Yorkshire. Ground investigation works were completed prior to work commencing both for the planning stage and practical contracting purposes. Ground conditions over the proposed sewer route were shown to comprise very stiff clay. TSL has extensive experience of this type of installation and used a Guided Auger Boring system for the work. This option was chosen due to its ability to install the concrete sewer pipes to the required line, level and gradient.
TSL used a Perforator PBA85V auger boring machine along with a Perforator HS90 hydraulic Powerpack, Bentonite Pump and tank, and OEN camera-based navigation unit to ensure the accuracy of the pilot bore installation. The company operates what it claims to be the largest fleet of
Perforator auger boring machines in the UK. The project called for the installation of some 370 m of DN450 FP McCann Concrete Jacking Pipe.
Work started on 20 July 2020, with a completion date of not later than 31 October 2020 being required due to the S50 notice and various restrictions implemented by United Utilities.
HARD GROUND
During the course of the boring works, the TSL crew encountered problems with the ground being much harder than anticipated. This was however overcome by using a polymer mix during the drilling works which eased the pressures incurred on rotation. Also, unexpected services were found when excavating the launch and reception pits which had an impact upon the speed at which the crew could work due to the care that had to be taken working near existing services.
The construction works were also phased so that residents homes would be accessible at all times and only limited households would have driveways blocked at any given time. The works were carried out using a rolling work area as the installations progressed through the scheme. Previous pits were reinstated before new pits were opened up in order to limit the effect the works had on local residents.
Overall the flood alleviation project was estimated to cost around £2 million, with the new sewer installation being some £80,000 in value.
Commenting on the project for the Main Contractor Patrick Donnellan – Commercial Director for Bethell Construction said: “Trenchless Solutions Ltd worked with us from design stage to completion on this project, they often went the extra mile by working additional hours/days in order to complete this very complex and restrictive project within budget and the deadline of 31 Oct which was ultimately achieved thanks to their expertise.” Website: www.trenchlesssolutions.co.uk
