This construction job story, "Keep on Boring," ran in the November 2017 issue of Foundation Drilling Magazine. It also ran in several American, Canadian, and European construction magazines.

1. November 2017
26 NORTH AMERICA
T
o say that Deep Founda-
tions Contractors (Deep)
was drilling in a confined
space within an extraction shaft on
the Eglinton Crosstown Light Rail
Transit Project (Crosstown) would
be an understatement.
It was the first of many chal-
lenges the firm would overcome
while working above and below
the buzzing streets of Midtown
Toronto, Canada. The epicentre of
the action, however, was a 32.5m
(107ft)-deep extraction shaft,
where two massive tunnel boring
machines (TBMs) would be lifted
from the ground at the end of
a long subterranean journey.
While Deep has extensive
experience working in Toronto,
there is nothing simple about
drilling in a crowded urban
environment. The Canadian
foundation contractor’s challenges
included inconsistent soil condi-
tions, low-clearance drilling,
unmovable utilities, maintaining
traffic and darkened confined
working spaces.
TRANSIT EXPANSION
Crosstown is a C$8.4 billion
(US$6.6 billion) infrastructure
project with a 19km corridor,
10km of which is underground.
Phase 2 includes the easternmost
tunnel. Come 2021, Metrolinx
projects that 5,500 passengers
per hour will benefit from this
project – the largest transit
expansion in Toronto history.
The Phase 2 contract was
awarded to the Aecon/ACS
Dragados Joint Venture in Novem-
ber 2013. Its scope entailed
3.25km of 6.5m-diameter twin
tunnels, precast concrete tunnel
lining segments, launch and
retrieval shafts, headwalls associ-
ated with future stations, two
emergency exit buildings, three
cross passages, utility relocations,
traffic staging, ground and
building settlement monitoring,
and site restoration.
Deep specialises in shoring for
a wide cross-section of building
and infrastructure projects. The
contractor was a natural fit having
worked on large transportation
projects, the most recent of which
was a subway extension for the
Toronto Transit Commission. The
Aecon/ACS Dragados JV awarded
Deep a roughly C$21 million
contract to excavate and shore
launch extraction shafts for two
TBMs, build two emergency exits
for the TBMs, and construct head
walls for two future stations. Its
work started in April 2014 and
concluded in March 2017.
KEEP THE TBMS BORING
Deep’s work would allow the two
TBMs, known as Don and Humber,
to continue underground uninter-
rupted. Stopping their progress
would be prohibitively expensive;
failure was not an option.
The Caterpillar TBMs – named
after two of Toronto’s rivers –
began tunnelling on September
30, 2015. The pair would crawl
westbound, digging 3.5km from
the launch shaft at Eglinton and
Leslie Streets before reaching
their destination. The TBMs would
eventually be hoisted out of
Extraction Shaft 3 (ES-3), which
sits at Yonge and Eglinton Streets,
Midtown Toronto’s busiest
intersection. Deep’s goal was to
prepare the shaft for their arrival.
FLEET OF BAUER RIGS
The ace Deep held in its pocket
was Canada’s largest fleet of
Bauer drilling rigs, all of which
were acquired from Equipment
Corporation of America (ECA).
Deep purchased the BG 55 –
one of the most powerful rotary
drilling rigs on the market at the
time with 553kNm of torque – in
September 2016. The contractor
then acquired one of the small-
est, a BG 11 H, in August 2017.
ECA also sold Deep seven Klemm
drilling rigs.
“We have the biggest fleet of
Bauers in Canada,” says Conor
Foy, Deep’s supervisor on the
Crosstown. According to ECA
Canada’s branch manager Ray
Kemppainen, Deep geared up
by purchasing five more rigs from
late 2015 to early 2016, including
a BG 46, two BG 39s, a BG 40 and
a BG 30.
In the early 2000s, Deep
analysed the drill-rig manufactur-
ing market and made a calculated
decision to acquire Bauer rigs.
Kemppainen recalls the 1970s
when the firm was buying
foundation equipment from his
former employer, Special Con-
struction Machines, known today
as ECA Canada. Deep is now
ECA’s largest Canadian client.
Deep was using conventional
crane-mounted drilling equipment
combined with vibratory hammers
to drive and extract casing in
urban environments, which is
more disruptive to residents and
motorists. Bauer technology
allows contractors to install and
remove sectional casings using its
rigs’ powerful hydraulic rotaries.
ECA was instrumental in
matching equipment to the
complexities of the Crosstown,
according to Foy. “There was a lot
of back and forth,” he says. “We
had to provide a lot of information
and work with them to get the
right equipment.”
Keep on boring
Deep Foundations drills to keep tunnel boring machines
crawling on Canada’s largest transit expansion
Deep used a
crane to lower
the BAUER BG
11 H drilling rig
into Extraction
Shaft 3
The mast of
the BG 11 H
was within
inches of the
lowest utility
support

2. 27
November 2017
FEATURE NAME 27NORTH AMERICA
The back and forth Foy refers
to revolves around service,
parts and training, according to
Kemppainen. He adds that Deep’s
managers were given authority to
order parts directly from the job
site, given the unforgiving
schedule and critical need to keep
the rigs drilling.
GROUND CONDITIONS
Midtown Toronto is notorious for
its troublesome ground condi-
tions. This reality sunk in as Deep
began drilling ES-3. The first 10m
included granular and silty sands.
Deep then hit the water table
and encountered flowing silt,
which went down 16m. A layer of
dense glacial till stretched from
26m to 32.5m below the surface.
The contractor overcame the soil
conditions with careful drilling
techniques and an assortment
of drilling buckets and tooling.
One challenge was unstable
soil. “The problem when it got
wet was the silty sand,” Foy
recalls. “It was very fluid, so you
had to follow proper procedures
to make sure the drilling was
consistent and you didn’t have
any cave-ins.” Deep relied
primarily on Bauer drilling buckets
to conquer the material. Augers
were used as a back-up and
bailers helped to remove water.
SHAFT WITHIN A SHAFT
Deep’s decision during the
tender process to tap Ontario-
based Isherwood Geostructural
Engineers as a shoring engineer
paid off. Working with Deep,
Isherwood engineered a creative
solution whereby a shaft could be
deepened just enough to allow
the Bauer BG 11 to go below
street level to install a secant wall
from within. After establishing
the dimensions of the rig and
surveying the lowest utility
supports, Deep determined that
lowering the grade to 15.5m and
pouring a temporary slab would
allow the BG 11 H to finish off
the secant wall.
Deep built ES-3 in two sections:
north and south. Each presented
a unique set of challenges.
The conflicting utilities in the
northern half were relocatable,
which allowed Deep to build a
secant pile wall by drilling from
the surface with one of its five
Bauer BG 40 drilling rigs. Fibre-
glass pile sections were used
on the east wall to prepare for
breakthrough by the TBMs.
Deep kept traffic flowing on
Eglinton Avenue by building a
temporary bridge deck over the
northern half once drilling was
completed. It consisted of timber
mats supported by steel beams
and bracing, and locked in place
with steel angle.
Once utilities were surveyed
and protected with steel sheeting,
Deep relocated its Bauer BG 40 to
start drilling in the southern half. It
was important to compare pile
and utility locations to avoid any
conflicts. The challenges with
confined space and drilling depths
faced in the northern half
remained, but all holes were
completed safely and efficiently.
Supporting utilities was Deep’s
top priority when excavating the
southern half of ES-3. The crew
built a lattice of steel support
beams to support the utility ducts/
conduits and mains running across
the shaft before commencing
work on the deck. Following a
rigorous inspection, this deck was
opened to traffic and the north
deck was removed. The north
would now remain open to allow
for removal of spoils, and eventu-
ally, the two TBMs.
Deep installed an internal waler
and lagging design to continue
shoring below the utilities, so that
The conflicting utilities in
the northern half were
relocatable, which allowed
Deep to build a secant
pile wall by drilling from
the surface with one of its
five Bauer BG 40s
The BG 11 came
as standard with
the ability to
remove the
upper section
for low-
headroom
applications
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3. November 2017
28 NORTH AMERICA
the slab could be poured for the
BG 11 H. The system, designed by
Isherwood Geostructural Engi-
neers, allowed the excavation to
be lowered enough for a compact
air track drill to drive soil nails. The
crew worked within a confined
space to install the nails and spray
shotcrete in a panel sequence to
keep the ground stable as
excavation continued. Alternating
panels allowed Deep to vertically
excavate up to 1.2m of material
every week. External dewatering
was required for the final two
levels, below the water table.
Most secant piles were accom-
plished from street level, but three
windows remained in the southern
half where that was not an option.
Closing them during the remain-
der of the excavation proved to
be the greatest challenge of the
complex ES-3 shaft construction.
The client dewatered ES-3 to
lower the water table by one
metre, so that the working
platform could be poured at the
correct elevation. The equipment
ran until the secant wall was
finished to keep the water at bay.
CONFINED SPACE
One of the most interesting
spectacles for passers-by was the
sight of a Bauer BG 11 H dan-
gling from the end of a crane line
as it slowly descended below
street level. Drilling within the
cavernous ES-3 was also one of
the more complex engineering
challenges Deep overcame.
“You barely had room to
breathe, especially inside the
shaft,” Foy says of ES-3, adding
that the mast of the BG 11 H was
within inches of the lowest utility
support. The height from the
drilling slab to the underside of
the utilities was 9.8m. “You had
to put in the preparation work
and make sure everyone knew
what they were doing and had
clear procedures for what was
happening.”
The compact rig excelled at
drilling in a confined space due
to its lower header configuration,
according to Kemppainen. Deep
was renting the rig from ECA
at the time, but converted to a
purchase because it was suited for
this operation.
Kemppainen explains: “The BG
11 comes standard with the ability
to remove the upper section for
low-headroom applications.
Deep removed the upper section
themselves, and ECA Canada
provided a shorter kelly bar for
the low-headroom application.”
“The BG 11 H was the only rig
that could fit under the decking
and utilities and still be able to
drill the required depth to
complete that wall,” Foy adds.
“This machine was dropped in
15m below ground surface, but it
still had to drill holes from inside
the shaft down another 17.8m.”
There were other selling points
for the BG 11 H too. At 35,000kg,
it could be safely lowered into
the excavation by a crane. The
rig’s ability to deliver 110kNm
(81,130ft-lb) of torque down
to a depth of 40m was a bonus.
Even though the BG 11 H was
compact enough to work beneath
the utilities, it was incapable of
using casing to drill the remaining
17.8m-long piles. Deep needed a
high-quality, water-tight secant
wall to keep the shaft dry.
The contractor chose a polymer
drilling fluid to keep the holes
open. A liner was inserted to keep
the top of the excavation open
and the fluid was pumped for the
remainder of the shaft. These
steps, with dewatering, created
enough head pressure to keep the
flowing silt from caving in.
The slurry bubbled in the tanks
at street level while being mixed
and agitated. Deep regularly
tested it for pH and viscosity
before turning on the constant
flow required during drilling.
Once the drill bit hit the
founding elevation, a drilling
bucket scooped out any leftover
chunks of earth. It was critical for
the slurry to keep the hole open
and clean, while Deep’s crews
built sectional piles in preparation
for concrete pouring.
LARGE PILES
The size of the piles forced Deep
to improvise. At 18m in length
and weighing 8,400kg, they were
too long to hoist in one piece and
too heavy for the BG 11 H to lift.
Deep designed a hoisting
device above each pile location
that could lower each of the three
six-metre sections to be bolted
together before eventually being
moved down to their founding
elevations. The hoist could lift
three 6m sections together.
Once the piles were installed to
the correct elevation, the concrete
was placed under polymer slurry
using the tremie method. The
crew poured each pile with a
flexible hose connected to a
sectional tremie pipe fed by a
pump above the shaft. The pipe
was then lowered to the bottom
of each hole. As the concrete was
placed, the slurry in each hole was
displaced.
Deep’s crews persevered 24
hours a day, six days a week to
complete the 29 secant piles
under a rigorous schedule. By this
time the northbound TBM had
already broken through. The
southbound TBM and a 50-person
crew were crawling quickly toward
ES-3. Deep had to be out of the
shaft before breakthrough.
On March 13, 2017, the lower
drilling came to a conclusion. The
project was completed success-
fully to the satisfaction of all
parties involved, bringing the City
of Toronto about 3.5km closer to
increased mobility.
This article was written by Brian M. Fraley, Fraley Construction Marketing
The Deep team
celebrates the
breakthrough
of a TBM
Deep regularly
tested polymer
drilling slurry for
pH and viscosity
before turning
on the constant
flow required
during drilling