ground treatment works

Report
GROUND TREATMENT WORKS
COMPENSATION GROUTING FARRINGDON STATION
Client: CrossRail
Main Contractor: BFK (Bam-Ferrovial-Kier JV)
Site Location: Farringdon - Barbican
Subcontract Value: £11.1m
The construction of the new Farringdon Station within the
C435 Crossrail contract requires ground treatment works
to secure a safe ground behaviour and protect the nearby
assets and structures. These works are being carried out
by Geocisa UK and they mainly consist of compensation
grouting, For that purpose, five grouting shafts were
installed in the new station area and along the new
tunnel route. The injection of cement grout through tubeà-manchette (TAM) pipes installed in the ground is being
performed to compensate the movements produced by
the excavation of the main two tunnels using Tunnel
Boring Machines (TBMs) and also during the enlargement
of those tunnels between the West Ticket Hall
(Farringdon) and the East Ticket Hall (Barbican) and the
excavation of the different station galleries and the
aforementioned ticket halls.
This location, at the heart of the City of London, it is a
very congested and built up area with in-use London
Underground and National Rail tracks, important heritage
buildings, very sensitive structures, sewers and all kinds
of services.
GEOLOGY
The ground in this area consists of 6-10m of Made
Ground and 4-7m of London Clay. Beneath those two
layers, Lambeth Group Formation is encountered. During
the drilling phase, all the TAMs were installed in the
London Clay layer, except for the ones installed in
Buther’s Ramp Shaft, that were installed in the Lambeth
Group with occasional but important presence of water.
Figure 1: longitudinal Section & geology
6 Mitre Passage, Floor 8 - Greenwich Peninsula - London, SE10 0ER
INFO: +44 0203 4407 061 - [email protected]
GROUND TREATMENT WORKS
PHASE 1: DRILLING
Horizontal drill holes were laid-out covering the influence
zone of all the tunnels and cross passages. A total of
357No. boreholes were drilled and inside each of them
steel TAM pipes with valves every 0.5m were installed.
The drill holes were installed in the London Clay and
Lambeth Group with lengths varying from 5m up to 84m
long.
Figure 2: Longitudinal Section
Figure 3: BR Shaft - Concurrent Grouting Vertical Movements
PHASE 2: GROUTING OPERATIONS
PRE-TREATMENT. This is the phase when the grouting is
carried out prior to the commencement of settlement as
a result of excavation, so as to verify that the grouting
system is active and that controlled movement of the
protected assets can be produced. This phase was
completed before the TBMs arrival according to the
contractual requirements, allowing a safe and controlled
TBM passing through the Farringdon Station work site.
JACKING. This phase is defined as episodes of grouting
designed specifically to produced controlled uplift which
are either:
PRE-JACKING: grouting performed in an area prior to any
construction activity that may induce settlements.
POST-JACKING: grouting performed after settlement
inducing construction activities, but which are not directly
related to any current excavation.
COMPENSATION GROUTING. This grouting is carried out
simultaneously with settlement inducing construction
activities to mitigate ground movements as they are
generated. This operation requires a continuous
coordination and feedback with the SCL tunnel team.
With highly challenging and demanding criteria, the
grouting works are successfully complying with the KC21
specification from CRL.
CHS
No. drillholes
These grouting works are developed in close coordination
between the Grouting and Instrumentation & Monitoring
(I&M) teams to control the ground movements.
All these stages are summarized in the previous figures
and in the table below:
MS1
MS2
MS3
BR
66
63
99
37
92
TOTAL length drilled (m)
2,621
3,985
4,432
2,362
4,686
Average borehole length (m)
39.71
63.25
44.77
63.84
50.93
Pre-Treatment (Y/N)





Pre-Jacking (Y/N)

Post-Jacking (Y/N)




Compensation Grouting (Y/N)
TOTAL Vol. grouting (m3)
59.54
35.65
98.67
28.58

354.4
TOTAL
18,086
576.86
6 Mitre Passage, Floor 8 - Greenwich Peninsula - London, SE10 0ER
INFO: +44 0203 440 7063 – [email protected]

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