HomeMy WebLinkAboutEGD-020-10Clarin~ton
Leading the Way
REPORT
ENGINEERING SERVICES DEPARTMENT
Meeting: GENERAL PURPOSE AND ADMINISTRATION COMMITTEE
Date: June 21, 2010 Resolution #: ~P~ ^c~ 74 /b
Report #: EGD-020-10 File #: By-law #:_
Subject: MILL STREET PEDESTRIAN TUNNEL STATUS UPDATE-
NEWCASTLE VILLAGE
Recommendations:
It is respectfully recommended that the General Purpose and Administration Committee
recommend to Council the following:
1. THAT Report EGD-020-10 be received;
2. THAT the Municipality endorse the selection of the Steel Pipe Roof Reinforcement
method of construction recommended by AECOM as detailed within this report;
3. THAT the Municipality endorse the Proposed Construction Schedule as attached;
4. THAT a copy of this report be forwarded to the Canadian Transport Agency,
Transport Canada and the Canadian National Railway.
Respectfully by,
Su fitted b~A:B: Cannella R ewed by: Franklin Wu
Director of Engineering Services // r Chief Administrative Officer
ASC/bb/jb/dv %~J•~
June 16, 2010
CORPORATION OF THE MUNICIPALITY OF CLARINGTON
40 TEMPERANCE STREET, BOWMANVILLE, ONTARIO L1C 3A6 T 905-623-3379 F 905-623-9282
REPORT NO.: EGD-020-10
PAGE 2
1.0 BACKGROUND
1.1 On May 5, 2009 a meeting was convened with the Canadian Transportation
Agency (CTA), CN Rail, Transport Canada, Municipal Staff, and the
Municipality's engineering consultant, AECOM, to begin a facilitation process
between the Municipality of Clarington and CN Rail in an effort to move
construction of the Mill Street Pedestrian Tunnel forward. All relevant
background, past and present issues were discussed, with the majority of the
Municipality's concerns including design review, cost-sharing, construction
scheduling and commitments by CN Rail for their staff involvement in the project.
A proposed construction schedule was agreed to and all parties committed to a
construction target date commencing in or about October of 2009 contingent on
approval of an acceptable construction approach.
1.2 At this meeting, representatives from CN and the Municipality also proposed to
enter into a formal cost-sharing agreement, subject to approval by both parties, in
which CN Rail will make a capital contribution of 15% (to a maximum of
$300,000) towards the construction costs for the Mill Street pedestrian tunnel and
the Municipality will be responsible for the structural and operational maintenance
of the tunnel. By-law 2009-70 authorizes the execution of the Agreement with
CN on behalf of the Municipality.
1.3 Efforts have since been made to establish a feasible design option that supports
CN guidelines and requirements for the project as well as environmental
requirements that were originally established in the MiII Street Environmental
Study Report (ESR). Golder Associates was commissioned to prepare a soils
report based on AECOM's initial design for the project which was based on
conventional Canadian tunnel-building technology where vertical piles are driven
into the railway embankment, temporary bridges placed and sheeting installed to
stabilize soils during excavation. A draft version of the report was received by
AECOM in September of 2009.
REPORT NO.: EGD-020-10 PAGE 3
1.4 Due to complex construction requirements and unique soil properties, Golder
expressed concern in the initial draft of their report over the potential for
sloughing and loss of ground beneath the rail bed and the potentially devastating
consequences that could occur during excavation. The report outlined additional
measures that could be taken to mitigate these concerns; however, AECOM was
concerned that, due to the added complexities and associated risks involved, CN
would be more inclined to approve anon-traditional tunnelling approach rather
than AECOM's initial design. As such, a decision was made to pursue other
viable alternatives.
1.5 Some delay to the originally proposed construction schedule was involved at this
point so that AECOM could assemble its wider expertise to investigate all options
at its disposal and find a workable solution for the project. Proven technologies
from the United States, the U.K. and Belgium were considered in conjunction
with Canadian methods and research eventually centred on two tunnelling
options: 1) the Jacked Tunnel and 2) Steel Pipe Arch Methods. Golder updated
their report upon review of these options and submitted a revised draft to
AECOM in April of 2010. Given the potential benefits of the newly proposed
options, Golder indicated that established Canadian methods of tunnel
construction would expose the Municipality to comparatively high risk, high cost
and the possible creation of an unconstructable excavation support system.
1.6 Based on Golder's April 2010 report and ongoing research by AECOM, options
for tunnel construction were revised, expanded upon and submitted in a technical
memo to CN (Attachment 1) for their consideration. Of the five options outlined in
the memo, the Steel Pipe Roof Reinforcement Method was identified by AECOM
as the preferred option. Subsequent discussions with representatives from the
Municipality, Golder, AECOM and CN regarding the preferred option were very
positive due to a lower associated risk and lack of complexity when compared to
the remaining options. During discussions, the CN representative envisioned
potential nation-wide application of the technology as an alternative to current
REPORT NO.: EGD-020-10
PAGE 4
Canadian technology for similar projects where the right soil conditions are
present, similar to those at the Mill Street location.
2.0 PROPOSED APPROACH
2.1 The Steel Pipe Roof Reinforcement Method has been employed widely for the
construction of small diameter tunnels in the United States over the last several
decades and as early as the 1960's for the construction of the Antwerp Metro
Station in Belgium. This method is a proven, time-tested alternative specifically
suited for projects where challenging soil conditions are encountered and where
conventional methods of tunnel construction are constrained by the need to
ensure uninterrupted overhead rail/vehicular traffic or are unable to mitigate
environmental impacts associated with the project. Local expertise in the
implementation of this method is available through the Mississauga office of
Earth Boring Company Ltd. The company has employed the technology in many
similar projects throughout North America and is currently considering it for a
project with the Toronto Transit Commission (TTC).
2.2 The conventional method of construction requires that vertical piles be driven or
angered into the railway embankment during very restricted CN-imposed
construction windows which are, by necessity, scheduled for overnight weekend
hours only. Because of the limited work window, this pile driving could potentially
continue for several months, depending on CN requirements and the likelihood
of unanticipated work stoppages. Disruption to local residents will be a major
concern should this method of construction be employed.
2.3 The Steel Pipe Reinforcement Method essentially solves this challenge by
removing the need to work on the CN Rail embankment. The method uses steel
pipes (piles) which are driven horizontally into position to form a reinforced layer
between tunnel excavations and the soil mass above (see Attachment 1). Steel
ribs are then installed as excavation proceeds, further enhancing the stability of
the tunnel lining. With this layer in place, ground surface settlement and forward
drag of the rail bed above the reinforced layer is substantially reduced when final
REPORT NO.: EGD-020-10
PAGE 5
tunnel construction occurs, mitigating one of CN's more pressing concerns.
2.4 Based on available borehole information, soil conditions are well-suited for this
method of construction and horizontal piles are expected to encounter no
significant obstructions (boulders, etc.). To minimize risk associated with the
driving of piles and excavation, CN has searched available records and
confirmed that no record of a historical structure within the embankment in the
vicinity of the proposed tunnel exists. A third party consultant with extensive
experience in unique tunnelling projects has also been added to the project team
to review the project and the preferred methodology as a measure to confirm
assumptions with regard to risk and constructability. This consultant was the VP
of the consulting firm responsible for the Sheppard subway construction.
2.5 Horizontal test piles will be driven and test holes augured as a means to further
mitigate potential risks by directly testing existing soil conditions at the exact
location and configuration of the proposed tunnel. This demonstration will also
act as part of apre-qualification process for prospective piling sub-contractors
prior to tendering. Golder Associates has agreed to retain a suitable contractor
on behalf of the Municipality to perform this test and demonstration.
2.6 AECOM's Markham office has consulted with Earth Boring Company Ltd. and is
in the process of determining the structural requirements for fabrication of the
horizontal steel piles, necessary invert elevations for the tunnel and the preferred
geometry for construction of the steel pipe reinforced tunnel lining. Preliminary
design under the proposed method is currently advancing and, subject to Council
endorsement and CN staff approval, will proceed to completion as per the
proposed project schedule (attachment 2).
3.0 BENEFITS TO PROPOSED APPROACH
3.1 The Steel Pipe Roof Reinforcement method offers significant benefits for
construction of the Mill Street Pedestrian tunnel that conventional methods
cannot mitigate, including the following:
REPORT NO.: EGD-020-10
PAGE 6
• The existing rail bed is left intact and useable throughout the entire
construction process
• The need for pile-driving or augering during very restricted CN-imposed
construction windows (late night/ early morning weekend hours) is eliminated
and, as such, all works can be completed during regular industry-established
day-time construction schedules and daylight hours eliminating this very
disruptive disturbance to the public during the weekends
• The contractor will not be subject to costly delays due to potential
interruptions and CN rail traffic requirements
• The cost of hiring CN Flagmen, who are currently in short supply and
available only on a restricted basis, is reduced.
• Overall construction period for tunnelling will be shortened by an estimated
50%, representing approximately 4 weeks.
4.0 RECOMMENDATIONS
4.1 Upon careful consideration of available options, scheduling commitments, CN-
imposed construction limitations, and in an effort to proactively manage public
expectation and ESR requirements, Municipal staff recommends Alternative 2-
Steel Pipe Roof Reinforcement as the preferred option.
Attachments:
Attachment 1-AECOM technical memo to CN (April 16, 2010)
Attachment 2-Proposed Project Schedule
ATTACHMENT N0.:1
REPORT NO.: EGD-020-10
e=MM AECO!v:
IL~rV 51301hs1on Street B053722~21 tel
Cobourg, ON, Canatla KBA SG6 9053723621 fax
www.aecom.com
Memorandum
re Will McCrae
Page
cc Andy Schell; Ron Albright, Derek Zoldy
snbjecl Mill Street Tunnelling OptionsTechnical Design Memorandum
r,em Hamid Javady
Dale Apri16,2010 Pm]eciNUmber 12-10948
Design Note for Proposed Mill Street Pedestrian Tunnel
Because of the existing structures, utilities and in particular the active commuter train line, the owner
and CN Rail are concerned about surface settlement and caving.
The design calls for a compartment breast boarded shield, and back grouting to prevent subsidence.
Construction of the underpass will mainly be through the loose silty sand, loose sandy silt, loose
sand, as well as loose sandy silt with some clay by the tunnel invert.
The condition dictated a shallow tunnel, with only 1.7m overburden. However, in discussions with CN
Rail it was apparent that the railroad would not approve open-cut construction because of the
disruption to fts operation on the mainline.
The tunnelling in this alignment would be challenging given the sensitivity of the railroad track above
and the fill materials through which the tunnel would need to be constructed. Some sheet piling at the
entrance and exit of the tunnel will be necessary.
A number of options were considered for tunnelling in soft ground under a major commuter rail.
These options are:
1.1 Alternative 1:
Jacked Tunne! Method
This method has been used successfully in other locations principally outside Canada, United States
and Europe. The method provides significant mitigation for concerns including: railroad operations
and reduction of interdependence of rail work to support construction by the contractor.
Since the tunnel-jacking method eliminates any relocation of the railroad tracks, the possibility ofpre-
excavationfor obstruction removal was eliminated, mandating that all obstructions be removed from
the face of the tunnel as itis being jacked. A metal jacking shield placed on the lead tunnel section is
to be constructed with multiple cells that provide work stations at any location of the tunnel face for
mining and obstruction removal. As excavation ahead of the cutting plate is not permitted, ground
which supports and surrounds obstmctions must first be stabilized by both mechanical means and
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/~~r~I Mnn °rantlum
April 16, 2p10
grouting prior to removal to prevent unacceptable loss of ground with resulting excessive surface and
subsurface movement.
The proposed measures to stabilize the soil face include dewatering, grouting, soil nailing, forepoling,
and use of retractable support grillage in each compartment of the jacking shield. The other major
issue associated with tunnel jacking is the settlement of railroad tracks during dewatering and tunnel
jacking.
The jacked box method involves constructing a reinforced concrete box alongside an embankment.
A hooded cutting edge is attached to the front of the box and hydraulic jacks push the whole structure
forward. Soil is excavated as the box advances. Support of the face can be provided by spites and
breasting plates as tunneling progresses. In raveling soils, ground improvement methods such as
permeation grouting, jet grouting, dewatering or ground freezing maybe necessary. High friction
between a moving tunnel and surrounding soil can lead to a tendency for the ground to move forward
with the box. These problems are reduced by constructing the box to stringent tolerances and by
installation of grease steel cables or other devices between the tunnel and ground to reduce drag.
The maximum thrust required is typically 50-70% of the weight of the box but is also a function of
tunnel length and cross sectional area.
The monitoring program will be necessary for railroads. To support timely measurements of track
movements, the project is surveying tracks up to three times per day. To mitigate impacts to railroad
operations caused by track settlements, railroad forces and equipment will be assigned directly to the
Project to insure immediate response for required track maintenance. There is heaving issue of soil
cause by jacking which cause lift the railroad tracks. Monitoring of the surface settlement during
construction will be on-going two times per day.
Figure 1: Precast Box
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Memorandum
Aprll 16, 2010
Table 1: Jack Box Tunnel Project
Projects Size Cover Date Ground condition Ground treatment
Pedestrian and cyclist L=30m 1.7m 1989 SII4stone 1111 overlying soft clay None
subway, UK W=5.9m '
H=3.6m
Highway tunnel, UK L=30m 8m 1991 Chalk with swallow holes loosely filled with sand Dewatering of sand
W=16.Sm
H=9.5m
Rail Tunnel, London, UK L=48m 1.7m 1998 Loose silt and sand overlying soft clay None
W=17m
H=6.2m
Lewisham Railway, UK L=32m 2m 1998 Loose silt and sand overlying soft clay None
W=4.4m
H=3.65m
Flood relief culvert, UK L=50m 6m 1999 Clayey granular fill overlying water bearing sands Ground freezing
W=23m and gravels, overlying weather cha~k
H=9.Sm
Highway Tunnel, L=106.8m 6m 2001 Weak water bearing strata with numerous man ( Ground freezing
Boston, USA W=24m made structure '
H=10.8m
Highway underbridge, L=45m 1.6m 2002 Fuel ash and clay fill overlying strff clay with rock None
UK W=14m inclusion
H=B.Sm
1.2 Alfernative 2:
Steel Pipe Roof Reinforcement
Tunnel displacement causes deformation of the ground between the tunnel and the ground surface
and hence results in subsidence at the ground surface. Jacked steel pipes are used to form a
reinforced layer between the driven tunnel and the soil-mass above the tunnel to reduce the potential
surface settlement.
Ground surface settlement due to tunnelling in soft ground is a major concern in all aspects of tunnel
design. The surface settlement is caused by a combination of ground loss at the tunnel, which
includes the ground loss at the tunnel face, convergence of the tunnel cavity and the closure of the
physical gap between the concrete lining and the ground.
Ground loss at the tunnel is consequentially translated into an equivalent surface depression
especially in cohesive soil and when tunnelling in shallow ground.
Anew method of reinforcing tunnel excavation and reducing the effect of ground loss at the tunnel is
to create a boundary of high stiffness between the ground surface and the tunnel. In order to enhance
soil properties before tunnelling, steel pipes can be jacked over the perimeter tunnel either in
rectangle or horse-shoe typed arrangements to form a layer of reinforced ground between the
proposed tunnel core and the ground surface.
The reinforced layer prevents the flow of soil into the tunnel at the periphery and at the face when the
excavator is driven through. Consequently, ground surface settlement is reduced substantially as the
translation of the movement of the ground loss at the tunnel is reduced by the reinforced layer of steel
pipes. Concrete lining is installed to further enhance the stability of the tunnel.
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~~I Memorandum
APtlI 18, 2410
This method has been widely used for construction of small diameter tunnels in the United States
(Rhodes and Kauschinger, 1996). However, this method has in fact been used in the early 1960s in
Belgium for the construction of the Antwerp Metro station (Hoste, 1980). The tunnel with 52m length
on the metropolitan Atlanta Rapid Transit system in Atlanta, Georgia, in 1991, was excavated by steel
pipe roof. The minimum overburden in this tunnel was 1.5m.
1.3 Alternative 3:
Sequence Excavation Method
Grouting will be injected from the surface and involves drilling a small diameter hole to the required
depth. Fluids are then injected through a special drill bit and ejected horizontally through a nozzle at
a high velocity into the ground. Based on the expected jet-grouted column diameter, a pattern of
holes at 1 mcenter-to-center will be considered.
The railroad undercrossing presents its own special difficulties. The embankment requires a drill
bench on both sides of the track so that angled drilling can be performed under the operating track.
In addition, special controls will be instituted with the drilling and grouting procedure to avoid heave
and lateral displacement. The construction sequence will be as follows:
1. Jet-grouting from the surface
2. Creation of a layer of improved ground around the crown of the tunnel by horizontal jet
grouting or forepoling in advance at depth of 2m
3. Advance of top heading
4. Placing steel ribs and liner plate
5. Back-grouting behind of liner plate in every 2m advance
Repeat the cycle from No.2 to No.5 until top heading of tunnel completed
1. Excavation of benching and extend the support and back grouting
2. Completion of final concrete lining
The shape of tunnel will be horseshoe as the arch will provide more stability. The support will be steel
ribs with metal lagging. The mini-excavator ormini-roadheader can be used for tunnel excavation.
Following the completion of the tunnel drive, the final lining will be constructed inside the tunnel. The
final lining will be cast-in-place concrete and constructed by using a traveling steel tunnel form.
Monitoring of surface settlement will be on-going, two times per day, before and after the beginning
of tunnelling.
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Apri116, 2010
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1.4 Alternative 4:
Ground Freezing
Stabilize the soil by the use of ground freezing is another option. The purpose of this method is to
achieve maximum security for railroad infrastructure and operations by significantly increasing the
strength and stability of the soil at the tunnel.
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Figure 2: Horizontal Drill Rig
Figure 3: Corrugated Liner Plate Installation
A=COM
Page 6
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April i6, 2010
The freezing method will increase the efficiency and safety of obstruction removal by holding
obstructions in place and providing a positive means of preventing run-in of material during
obstruction removal.
The major issue is the heaving of the soil caused by ground freezing which in turn will lift the railroad
tracks.
The contractorforthis method is not available in Toronto.
T.5 Alternative 5:
Pedestrian Bridge
The pedestrian bridge provides adequate space for sidewalks and biking for the community.
,<.KK,
Figure 4: Pedestrian Tunnel
2. Preliminary Assessment of Construction Method and Constructability
Issues
The preliminary designs include a site map, tunnel plan and profile, and typical tunnel.
Horizontal jet grouting around the tunnel's perimeter before opening the tunnel lowers the risk for
settlement and heaving of ground under the railway. Jet-grouting is a method which uses the effect of
shearing and disintegrating the soil by exposing it to the operation of a cement grout jet.
Based on preliminary geotechnical information, a is anticipated that soft ground tunneling methods
will be appropriate. The horseshoe shape of the tunnel will provide more ground stability. The support
will use steel ribs with metal lagging. The mini-excavator ormini-roadheader can be used for tunnel
driving.
The major risks were identified are:
1. Settlement or heaving of the railroad tracks
2. Encountering obstructions that could not be removed
3. Heterogeneous soil conditions due to tunneling in fill materials
4. Flowing ground condtions at the tunnel
Based on the result of geotechnical investigations, groundwater is not expected to be encountered or
significantly affectthe tunneling operation.
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To control ground loss or heave, ground improvement from the surface and in the tunnel will be
necessary. Due to the possibility of encountering boulders and obstructions, the machine is required
to have a boom excavator to excavate and remove obstructions.
To control flowing ground at the tunnel face, stabilization of the face by forepoling, horizontal jet-
groutingand close face operation will be necessary. Surface grouting will also stabilize the tunneling
operation.
In order to ensure minimal impact to the railroad operation, the contractor will be required to
coordinate tunneling with the railroad's schedule to minimize tunnelling under tracks that are in use.
In addition, extensive monitoring of settlement points on and adjacent to the track will be required on
a daily basis.
Selecting the optimal construction method: Factors to be considered when assessing alternative
construction methods include cost, schedule, aversion to risk, ground cover, soil conditions, space
availability and predicted settlement. If we consider cost of a shallow cut and cover as 100, then
relative cost of equivalent tunnel construction methods would be as follows:
1. Ribs and lagging, 150
2. Jacked Box, 170
3. Steel Piping roof, 180
End of Memorandum
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