Fleetwood WwTW (United Utilities)

Jet Grouting

LANCASHIRE, U.K.

Scope of Works;

The works consisted of 98 No., 1.4 to 2.0m diameter

overlapping columns, 3.5m to 5.0m in length, formed

at a depth of 20m to 25m below ground level,

creating a homogeneous grout block along the length

of the tunnel drive, reducing the risk of tunnelling ac-

tivities in the water bearing and tidal sands.

Bachy Soletanche Specialist Geotechnics successfully completed this Jet Grouting project for tunnelling contractor A E Yates Trenchless Solutions as part of the refurbishment of the Fleetwood Wastewater Treatment Works, which will allow United Utilities to store and treat excess water during storms - protecting Blackpool’s beaches and bathing waters.

The project required improvement of the ground conditions that would be encountered during tunnel construction, prior to the construction of a 35m long, 1.8m ID connection tunnel between three diaphragm wall storm water storage shafts. These shafts were previously constructed by Bachy Soletanche, as part of the continual upgrade to the existing treatment plant.

The main purpose of the ground treatment was to modify the soils present, homogenising the water bearing strata in the upper split face of the proposed tunnel bore, to properties similar to that of the underlying stiff clay. The increase in soil strength and stiffness were required to minimise the risk of the tunnel boring machine (TBM) going off course and reduce the potential overbreak and hence settlement above the tunnel drive.

In addition to these works, a further requirement was to create three ‘breakout’ treatment blocks, which have been designed to reduce the permeability and increase the strength of the in-situ wet sands and silty soils to allow the shaft wall to be broken out by hand and the TBM to be launched.

C6XPJetting Rig, working adjacent to D-walled Shaft

A650

Jet Grouted Breakout Blocks and Ground Treatment for TBM/Hand Mined Connection Tunnels

CLIENT: United Utilities (UU)

CONSULTING ENGINEERS: U.U. & Donaldson

DURATION OF WORKS: 9 Weeks

www.bacsol.co.uk

Jet Grout Block, view of exposed face following coring and removal of Diaphragm Wall

TUNNELLING SUB-CONTRACTOR: A.E.Yates

PRINCIPAL CONTRACTOR: KMI+

A650

The works mitigated the risks

inherent to, and to assist with

aspects of, the tunnel

construction by providing a

homogenous material for the

tunnelling machine to progress

through and ground support to

exclude groundwater at the

tunnel break-out eyes, from

Tank T3 and Tank T4. Jet

grouting also ensured ground

support and exclude

groundwater for the T3-T1 open

face tunnel excavation.

A number of trial jet grout

columns were installed to

determine the required jetting

parameters for the main works.

The overlap and diameter of the

columns was confirmed using the

SolData Cyljet technique.

The design and construction of

the ‘breakout’ treatment blocks

became the most critical part of

the works undertaken. With a

requirement to provide a water

tight block sealed against the

diaphragm wall that would be

capable of retaining the

overburden material, consisting

of 25m of saturated sands and

silty soils subject to tidal

pressure, and the adjacent to the

shafts. These challenging

temporary works, to assist the

tunnel formation, meant we had

to draw on our expertise and

experience to deliver a quality

result to a critical and tight

programme to meet the summer

bathing season.

Another particularly high-risk area

of the project, was the section

between Tank 1 and Tank 4

where a short tunnel drive

(approx. 2m dia. by 2m length)

was required to be formed by

hand excavation. Within these

areas, treatment density was

increased to reduce the ‘gap risk’

and ensure a supportive block of

low permeability material sealed

against the shaft walls.

U.U. recognised that early

involvement with contractors

allowed it to mitigate ground risks

and achieve its programme and

its regulatory commitments to

the E.A. delivering the project 4

months before the bathing

season commenced .

www.bacsol.co.uk

SAA Testing of the Jet Grout Columns

Plan of Jet Grout Columns

SAA equipment for the Jet Grout Columns Jet Grouting Equipment

SAA equipment for the Jet Grout Columns

The Jet Grouting Process

Fleetwood WWTW & the Fylde Coastline