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
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