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TUNNEL BORING MACHINE (TBM) METHOD
There are two major shield methods around: earth pressure balanced (EPB) and slurry type shield machine. Selection of shield method depends on ground conditions, surface conditions, dimensions of the tunnel section, boring distance, tunnel alignment and construction period. Both are closed-face type shield machines, meaning the "head" part of machine is "closed" and separated from the rear part of machine. The "head" has a working chamber filled with soil or slurry between the cutting face and bulkhead to stabilize the cutting face under soil pressure . The EPB type shield machine turns the excavated soil into mud pressure and holds it under soil pressure to stabilize the cutting face. It has excavation system to cut the soil, mixing system to mix the excavated soil into mud pressure, soil discharge system to discharge the soil and control system to keep the soil pressure uniform. Therefore, EPB may not be applicable for the rocky soil that is difficult to turn the excavated soil into slurry. It can be used at ground predominated by clayer soil. The slurry type shield machine, on the other hand, uses the external pressurized slurry to stabilize the cutting face, similar to bored piles or diaphragm walls using bentonite to contain the trench wall. The slurry is circulated to transport the excavated soil by fluid conveyance. Besides having excavation system, the slurry type shield machine has slurry feed and discharge equipment to circulate and pressurize slurry and slurry processing equipment on the ground to adjust the slurry properties.
GENERAL KNOWLEDGE ABOUT TBM TUNNELS
A typical rail tunnel section with its components
Schematic construction sequence for TBM
A shield machine at factory ready to transport out to the site
Main components of a shield machine
EARTH PRESSURE BALANCED MACHINE (EPBM)
Schematic representation of EPBM
Typical site utilization plan for EPBM including working shaft, gantry crane, segment stock yard, tanks,
etc.
Section view of the EPBM site utilization
SLURRY TYPE TBM
Schematic representation of a slurry type shield machine
Cutting head sketch of slurry type shield
Typical site utilization plan for slurry type TBM including working shaft, gantry crane, segment stock yard, tanks, etc.
Section view of the site utilization for the slurry type TBM
SHAFT CONSTRUCTION
Shaft construction using diaphragm wall method (C905)
Shaft construction using diaphragm wall method (C902). Access stairs, ventilation and passenger
hoist are provided.
LAUNCHING AND OPERATION
Main body of the shield machine being lowered down into launching shaft. From there, the TBM
system is to be assembled and starts boring.
Lowering down the main body of shield machine into launching shaft
A receiving shaft to accommodate dismentle (right) and assemble (left) TBM at the same time (C902)
The function part of TBM (backup) at the rear (C902)
Work Sequece:
Lower main body, cutting head, segment erector, screw conveyer, tail shield, thrust frame > Assemble TBM > Erection of reaction frame > Connection of hose and cables > Installation of 4 to 5 nos. of temp segments > Initial drive > Completion of initial drive > Modification of TBM including removal of reaction frame, cradle and temp rings, laying rail > Main drive > Break through soft eye (reach receiving shaft) > Dismantle TBM
Notes: - Gantry crane (for example, 35ton, 45ton) is normally used crossing the shaft. - Lower down TBM components to the shaft needs heavy lifting. 600ton or 700ton crawler crane is needed. - TBM production rate depends on soil condition. Normally at 5-10 m/d. - Ground improvement is necessary at receiving shaft end for TBM to pass through (about 3-4m in length). Start end depends on ground conditions. - Grouting to the gap between shield skin and segment following segment installation from ground surface. - Dismantle TBM can be done in launch shaft after being transporting back from receiving shaft end to the launching shaft end, leaving behind shield skin at receiving shaft end.
LINING
The start end of tunnel lining (C902)
Lining segments are being lowered down from shaft to the locomotive
Close view of segment lining. A typical ring of lining: 1.4m width with 6 segemnts to be joined by bolts.
Note that the joint of neighbouring rings to be staggered (C902)
Completed tunnel with linings. From here, 1st stage concrete, rail track, ventilation, electrical and
other cables, etc., starts installation.
PIPE JACKING
Pipe Jacking, a smaller scale "TBM" method to lay sewer lines
TBM TERMINOLOGIES
Backfill Grouting (tailskin grout): Grouting to fill void between the lining and the ground (tail void) by grout injection Cycle Time: Segment erection > excavation / backfill grouting > segment erection EPB: Earth Pressure Balance (Shield Machine) Goliath Crane: Gantry crane Segment, Ring and Lining: Segment: a splice of precast concrete to form part of ring structure. This ring is also called primary lining. The inside surface is sprayed with concrete, usually for waterproofing and finishing. Also called secondary lining. Segment > Lining (primary, secondary), or ring Shaft: - To allow muck taken out, lining material brought in, TBM lowering in and assembly, reaction force at the start, operation space - Launching shaft, intermediate shaft, receiving shaft, turning shaft Screw Conveyor: Carry excavated rocks and earth from cutting face to the rear of the completed tunnel Muck: Soil slurry Overburden: Distance from top point of tunnel to the surface of ground. Usually 1 - 1.5D TBM: Tunnel Boring Machine
MAIN REFERENCES 1. Japanese standard for shield tunneling, third edition, 1996.
2. Mitsubishi Heavy Industries catalogue, 2005. 3. DTL 1 C902 (main contractor: Shanghai Tunnel), C905 (main contractor: Shimizu).
NEW AUSTRIAN TUNNELING METHOD (NATM)
The New Austrian Tunneling Method (NATM), an alternative and cheaper way for tunneling.
NATM support system sketch
MAIN REFERENCES Basler&Hofmann's catalogue
http://www.p3planningengineer.com/productivity/tunneling/tunneling.htm
Crossrail
8 giant tunnelling machines
1,000 tonnes in weight, 140 metres long - a giant underground factory on wheels
Meet our giant tunnelling machines
Digging the new tunnels was a 24-hour a day job, 7 days a week. Crossrail used eight tunnel
boring machines (TBMs) to construct the new rail tunnels under London. The giant machines
carefully weaved through the capital's congested sub-terrain, snaking between the existing
Tube network, sewers, utilities, and London’s hidden rivers at depths of up to 40 metres.
Like giant underground factories on rails, each of the custom made Crossrail tunnelling
machines had an external diameter of 7.1 metres, weighed around 1,000 tonnes and measure
around 150 metre in length – the equivalent of 14 London buses end-to-end and a staggering
143 buses in weight.
Each machine has a rotating cutterhead at the front and a series of trailers behind housing all
the mechanical and electrical equipment. The TBM is effectively a large metal cylinder with a
rotating cutting head at the front and conveyor belt at the back to remove the earth.
At the front of the TBM is a cutting wheel, which is pressed against the tunnel face by
hydraulic cylinders. Inside the cutting wheel the disc cutters and scraping tool loosen the
material. The loosened material is removed from the cutter head via a screw conveyor, which
moves the material through the back of the TBM and out of the tunnel via a conveyor belt.
The tunnel face is continuously monitored by pressure sensors that check the turning power
of the cutting wheel and the screw conveyor, keeping track of the material that has been
excavated. The TBM makes use of the concrete rings using hydraulic rams which are at the
back of the cutter. Once the machine has moved sufficient distance the next concrete ring is
installed. Crossrail’s concrete tunnel lining is designed to last 120 years.
An in-built laser guidance system enabled the tunnelling teams to ensure the machine remains
on course, ending up to within a millimetre of where it needs to be.
During Crossrail's tunnelling phase, each TBM was operated by ‘tunnel gangs’ comprising of
around twenty people – twelve people on the TBM itself and eight people working from the
rear of the machine to above ground. The tunnel gangs worked in 12 hour shifts, tunnelling
24 hours per day, 7 days per week.
Six earth pressure balance TBMs were used to construct around 18 kilometres of twin-bore
tunnels through clay to the West and the riverbed deposits in the east, while 2 mix-shield
machines were used to drive the tunnels through the chalk under the River Thames.
8 machines digging 10 individual tunnel drives
The eight TBMs undertook a total of ten individual tunnel drives to construct the new
6.2m diameter Crossrail tunnels.
The eight tunnel boring machines were used as follows:
Royal Oak to Farringdon (Drive X): Crossrail's first pair of tunnelling
machines, Phyllis and Ada, were delivered to Westbourne Park just west of
Paddington, in early 2012 where they were assembled and tested ahead of launch in
May and August respectively. The two machines tunnelled 6.8km each towards
Farringdon, completing their journeys in November 2013 and January 2014
respectively.
Limmo to Farringdon (Drive Y): Crossrail's second pair of TBMs, Elizabeth and
Victoria, were delivered to Limmo Peninsula in London’s Docklands in summer 2012
and lowered 40 metres below ground in October 2012 ahead of their launch. Together
they undertook the longest Crossrail tunnel drives, constructing 8.3km of new rail
tunnels between Limmo Peninsula, near Canning Town, and Farringdon.
Pudding Mill Lane to Stepney Green (Drive Z) & Limmo to Victoria Dock Portal
(Drive G): Tunnel boring machines Jessica and Ellie were used to construct
the 2.7km tunnel drives from Pudding Mill Lane portal, near Stratford, to Stepney
Green. The machines were then dismantled, lifted out of the shaft and transported by
road from Stepney Green to Limmo Peninsula, where they were relaunched to drive
the 0.9km tunnels from Limmo to Victoria Dock Portal. These were the only
machines on the project to undertake two separate tunnel drives.
Plumstead to North Woolwich Portal (Drive H): In south-east London, tunnelling
machines Sophia and Mary were used to construct the 2.9km long Thames Tunnel
between Plumstead portal and North Woolwich portal. They were Crossrail's only
mixed-shield, or "slurry", TBMs and at 110 metres in length are slightly shorter than
our other TBMs.
Start and end dates for each of the Crossrail TBMs
TUNNELLING
MACHINE
LAUNCHED
FROM DESTINATION
STARTED
TUNNELLING
COMPLETED
TUNNELLING
Phyllis Royal Oak Portal Farringdon 04/05/2012 08/10/2013
Ada Royal Oak Portal Farringdon 21/08/2012 24/01/2014
Elizabeth Limmo Peninsula Farringdon 29/11/2012 11/05/2015
Victoria Limmo Peninsula Farringdon 08/12/2012 26/05/2015
Sophia Plumstead Portal North Woolwich 09/01/2013 29/01/2014
Mary Plumstead Portal North Woolwich 19/05/2013 13/05/2014
Jessica - first drive Pudding Mill Lane Stepney Green 15/08/2013 05/02/2014
Ellie - first drive Pudding Mill Lane Stepney Green 26/02/2014 13/06/2014
Jessica - second drive Limmo Peninsula Victoria Dock Portal 02/06/2014 10/08/2014
Ellie - second drive Limmo Peninsula Victoria Dock Portal 11/09/2014 19/10/2014
Deepest point in Crossrail tunnels
42 metres at Finsbury Circus, near Liverpool Street station.
How many metres bored on the fastest day of tunnelling by a single machine?
72 metres by Ellie on 16 April 2014 between Pudding Mill Lane and Stepney Green.
Crossrail tunnelling progressed at a collective average of 38 metres per day.
Naming our tunnelling machines
According to tunnelling tradition, a TBM cannot start work until it is given a name.
This tradition is carried out throughout the world as a sign of good luck for the project
ahead. Since our TBMs operated in pairs to deliver the eastbound and westbound
tunnels for each of the tunnel drives, we decided to name them in pairs.
Our tunnelling machines were all named by members of the public following competitions
run via our website. The first six machines were named after historical London figures, whilst
the final two machines were named after modern day heroes.
Ada and Phyllis (submitted by Emma Duncan, London): Ada Lovelace was one of
the earliest computer scientists. She worked with Charles Babbage on his ‘analytical
engine’, and is regarded as having written the first computer program. Phyllis
Pearsall single-handedly created the London A-Z. A portrait painter, she got lost on
the way to a party in 1935 and decided the maps were inadequate. She walked 23,000
streets, and a total of 3,000 miles to compile the map, delivering the first 250 copies in
a wheelbarrow.
Victoria and Elizabeth (submitted by Bryan Evans, Burnham): Named after the
two Queens, Victoria was monarch in the first age of great railway engineering
projects and Elizabeth is the monarch at the advent of this great age of railway
engineering projects.
Mary and Sophia (submitted by Ray King, London): Mary was the wife of the
famous railway engineer Isambard Kingdom Brunel and Sophia was the wife of Marc
Isambard Brunel who built the first tunnel under the Thames.
Jessica and Ellie (submitted by students of Marion Richardson Primary School in
Stepney Green): Students from Marion Richardson Primary School in Stepney
suggested the names ‘Jessica’ and ‘Ellie’ for the final two of eight Crossrail
tunnelling machines, which will drive the tunnels from Pudding Mill Lane (near the
Queen Elizabeth Olympic Park to Stepney). Jessica Ennis-Hill and Ellie Simmonds
were both gold medallists from the London Olympics and Paralympics 2012.
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