Jet to it – Bachy Soletanche undertakes jet grouting for £18million wastewater utility refurbishment

Bachy Soletanche, one of the UK’s leading geotechnical specialists, has started jet grouting as part of an £18million refurbishment of the Fleetwood Wastewater Treatment Works. This will allow the North West’s water company United Utilities to store and treat excess water during storms and play its part in helping protect the Fylde Coasts beaches and bathing waters. Working with tunnelling contractor A E Yates Trenchless Solutions Ltd and main contractor KMI Plus, sees Bachy Soletanche Specialist Geotechnics unit undertake tunnelling preparation works, prior to the construction of a connection tunnel between three diaphragm wall storm water shafts. These shafts were constructed previously by Bachy Soletanche, as part of the continual upgrade to the existing treatment plant.

  • In order to improve the ground conditions that will be encountered during tunnel construction, the tunnelling contractor, AE Yates Trenchless Solutions, has employed Bachy Soletanche to undertake ground treatment by jet grouting
  • The ground treatment has been designed to modify the soils present above the underlying stiff clay – minimising water seepage and the risk of the tunnel boring machine (TBM) going off course
  • The overlapping jet grout columns will construct a homogeneous grout block along the length of the tunnel drive, which in turn improves the accuracy and rate of the TBM
  • On completion the works will boast 98no., 1.4 to 2.0m diameter columns at a depth of 5m and 3.55m long (approximately 20m to 25m below ground level)
  • In addition to these works, Bachy is working on a further requirement to create three ‘breakout’ treatment blocks, which have been designed to reduce the permeability and increase the strength of the virgin ground (wet sands and silty soils), that runs adjacent to their diaphragm shafts
  • This procedure is being implemented to allow the shaft wall to be broken out and the tunnel drive to be launched
    As part of the works, a number of trial jet grout columns are being installed to determine the required jetting parameters for the main works
  • The overlap and diameter of these columns will be confirmed using the innovative SolData Cyljet technique.
    For more information on Bachy Soletanche please visit its website, www.bacsol.co.uk, or follow the organisation on Twitter at twitter.com/bachysoletanche
  • Sewers are just one of a number of factors which can effect the quality of bathing waters, and in the North West are thought to contribute about a third of the problem where beaches fail the standards
  • Others significant sources of pollution include run-off from agricultural land and dirty rain washed from urban roads
  • For more information on how United Utilities is doing its bit at places like Fleetwood visit: www.unitedutilities.com/bathing-waters-doing

Gavin Clifford, Contracts Manager at Bachy Soletanche Specialist Geotechnics, commented:

This project was unique and delivered a number of challenges to say the least. A particularly noteworthy element of the project was the need to provide a homogeneous material with increased soil strength and reduced permeability with properties similar to those of the underlying clay. Anything weak or soft would allow the TBM to steer off course and not provide the required strength to gain support, whilst anything too strong would hinder the TBM dig rates. This required the design of a cementitious grout mix – capable of being mixed at a rate greater than 300ltr/min, pumped at 400bar for the jet grouting process and achieving a minimum UCS of 0.5MPa maximum of 3Mpa at 28 days!

This was achieved via a cement / bentonite mix with a water content ratio of 0.54. Despite the need to source a homogeneous material to increase soil strength, the design and construction of the ‘breakout’ treatment blocks became the most critical part of the works undertaken. With a requirement to provide a watertight block sealed against the diaphragm wall that would be capable of retaining the overburden material adjacent to the shafts, 25m of saturated sands and silty soils subject to tidal pressure, it was a challenging requirement we had to navigate carefully – drawing on our expertise and experience to deliver a quality result (These are temporary works to assist the dig).

It’s safe to say that this has been a technically challenging project, but a fantastic opportunity to showcase our expertise and deliver a truly innovative and purposeful result for the main contractor and ultimately the client. I would like to place particular attention on the skilled team that made these works a reality – particularly our Contracts Engineer, Steven Hickey and our Supervisor, Eddie McAllister.