1103-Sun Construction of Pipe Roof and Support System in Proposed Outlet Drain Under Crossing North...
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Transcript of 1103-Sun Construction of Pipe Roof and Support System in Proposed Outlet Drain Under Crossing North...
Construction of Pipe Roof and Support System in Proposed
Outlet Drain Undercrossing North Buona Vista Road, Singapore
T Sun, W& M Consultants, Singapore. [email protected] Mr. Chelliah_MURUGAMOORTHY, Land Transport Authority, Singapore,
Dr.Lingting Zhang, Or Kim Peow Contractors (Pte) Ltd, Singapore
Abstract: The project in the paper included design and construction of a permanent 120m long RC box culvert and
sewer diversion at North Buona Vista Road (NBV) Singapore. The pipe roof method was selected by the design
and build contractor in fulfilment of the contract requirement for the 53 m box section undercrossing NBV Road. The
adopted methodology comprised the installation by pipe jacking of numbers of interlocking steel pipes followed by
traverse series of steel frames for safe mining of the tunnel. This served to maintain uninterrupted service conditions for the
road, subways tunnel and other services. There are many challenges in the construction of pipe roof and mined tunnel. This
paper deals with the consideration in the design and construction of such works. It also highlighted the
problems encountered during the construction, subsequent solution adopted and protection of existing utilities as well as
monitoring of settlement of the surrounding areas of the project.
1. INTRUDUCTION:
The Land Transport Authority of Singapore (LTA)
Contract C 8288 for Tanglin Halt Outlet Drain at North
Buona Vista Road comprises the design and
construction of a 120m long permanent RC
(reinforcement concrete) box culvert, sewer diversion
and other related works located along Commonwealth
Avenue, Commonwealth Avenue West and North
Buona Vista Road.
Part of the works under this contract is the construction
of approximately 53m of drainage box culvert under-
crossing North Buona Vista Road using approved
tunneling method.
The Contractor Or Kim Peow Contractors (Pte) Ltd
(OKP) commenced the project on 15th December 2008
and the whole works were scheduled for completion on
14th December 2010.
The contract’s requirement mandated that uninterrupted,
smooth road and rail traffic be maintained, and that the
sewer and other utilities be protected against damages.
After careful consideration it was concluded that with the
adoption of pipe roof, mined tunnel method, the
requirements can be met. The outlet drain box culvert
under design and build contract was completed with
minimal deviations, good safety and quality standards
and within the time schedule and cost control.
The project was divided into various zones and areas as
shown in Fig 1. Fig 2 shows the longitudinal section view
along with the mined tunnel. The outer dimension of
drain is 7m wide by 5m high (inner 6m x 4 m). The
gradient of the proposed outlet drain is 0.1% ( 1: 1000).
Fig 1. Layout of proposed drainage box culvert
Fig 2. Longitudinal section of drainage box culvert
2. GEOLOGICAL / SITE CONDITION
The ground condition along the alignment of the mined
tunnel is given in LTA’s soil interpretative report (LTA
2009a). The profile is derived from the soil logs at
boreholes ABH 2, CC4739C, ABH 3 and ABH 4 and is
summarised in Fig 3.
Fig 3. General soil profile of the mined tunnel zone
The geotechnical design parameters adopted in the
design is shown in Table 1 (Parson B., 2009).
Table 1. Design soil parameters
3. DESIGN AND BUILD CONTRACT
The part of the contract involving the drain undercrossing
North Buona Vista Road was to be on a design and build
basis. The Contractor’s appointed design consultant
studied the soil condition and other information on the
project and designed the pipe roof over other method of
construction for the drain. This was achieved over
several months of presentations and detail proposal to
and close discussions with LTA and PUB (Public
Utilities Board), the later being the Authority which will
take over the drain upon its completion.
The key design considerations as detailed in various
communications with LTA(LTA 2009b) and other tender
and contract documents consisted of factors such as:
i. Geotechnical aspects, including soil-structure
interaction between pipe-roof and surrounding
ground, stability of the excavated face and
base stability during excavation;
ii. Structural aspects such as the design of the pipe-
roof and the structural steel frames supporting
the piped-roof;
iii. Soil improvements and types and extent of
protection to existing services;
iv. Other pertinent points related to method and
operation included: the adoption of 3 sided pipe
roof pipe, type and capabilities of jacking
machine used, their maintenance of face pressure,
excavation speed especially when encountered
with obstructions such as sheet piles, timber
pieces, skill of operators, details of pipe clutching
and damages expected to be caused by excessive
settlement , mitigation measures and others.
Risk assessment and hazard analysis including alert and
suspension levels for instrumentations such as
inclinometers and settlement markers were thoroughly
considered in the Report for Overall Constriction Impact
Assessment (CIAR) (Parson B. 2010) and adopted during
the construction stage.
4. CONSTRUCTION
4.1 Construction methodology
The temporary earth retaining structure to support the
ground during the excavation of the mined tunnel
consists of a series of 780mm diameter, 16mm thick
circular steel pipes interconnected by clutch to form an
inverted U pipe-roof structure around the footprint of
the proposed drain. This method known as pipe roof/
arch, have been deployed in USA and Singapore in the
last twenty years, as reported in Martha Railway
Underpass ,USA (Atalah, A.L. and D.T. Iseley, 1991)
Orchard-C.K .Tang Underpass Singapore (Darling, P.,
1993).
The pipe roof formed by 22 rows of steel pipes ,
comprised of 10 at the top and 6 on either side .They
were installed in predetermined sequence, starting from
the lead central row on top, and consecutively on left
and right before the vertical rows were done.
The interlocking steel pipes forming the pipe roof
together with the support system is shown in Fig 4.1 to
Fig 4.5
Fig 4.1 Transverse view of interlocking pipe roof
Fig 4.2 Details of Pipe Clutch
Fig 4.3 View of interlocking pipe roof with steel entrance frame
Fig 4.4 partially completed pipe roof
Fig 4.5 Complete pipe roof with interlocking pipes
The pipe roof (Parsons B 2009) is in-turn supported by
structural steel frames at every 1.5m’s interval. Each
excavation step is also 1.5m with the width of the
excavated slope also limited to 1.5m. Three sections of
soil improvements were provided and these are located at
the interfaces with the jacking shaft, the receiving shaft,
and a 10m zone at mid-point of the mined tunnel.
Drainage holes (2 nos.) were also provided to release any
built-up of excess pore-water pressure during the
excavation. Soil reinforcement in the form of
reinforcement bar arranged in a square grid pattern at
0.65 m spacing both ways, would be provided to
stabilize the face of the excavation in the F2 layer. The
face of the excavation would also be protected
temporarily during each stage excavation with a layer of
short-crete of 15mm thick.
After the pipe roof and the last portal frame( at the
tunnel opening into the receiving shaft) were installed,
the soldier piles and the sheet piles around the shaft were
cut. The permanent drain section inside the mined tunnel
between the jacking shaft and the receiving shaft were
then cast. Some of the piped-roof pipes were filled with
approved cement-based backfill material before the
casting of the final drain section, whereas others were
done after that to ensure that the steel pipes do not pose
any corrosion problems in the long run..
4. 2 Construction problems encountered
The major construction problems encountered include
those realted to utilities protecton, pipe jacking and
monitoring of settlements.
4.2.1 Protections of utilities
Many utilities were encountered in the project areas and
need to be diverted or protected. These were identified in
the CIAR Report ( Parsons, B 2010).
The West End line viaduct and the MRT (CCL 4& 5 )
Tunnel, which was laid some 4.4 m below the propsed
outlet drain were checked for the effect of the excaation
of the shafts, mined tunnel and found to have maximum
settlement of 6 mm, much less than the allwoable 15mm
according to LTA Civil Design Criteria ( LTA 2009 c)
and LTA Code of practice for RailWay Protecvtion.
(LTA.2009 d).
The plan and cross section view showing the utilities is given in Fig 5 and 6
Fig 5 Plan view showing major utilities
Fig 6 Cross section showing major utilities and the
relative distance from the proposed out let drain
Fig 7a shows the service MRT Line tunnels under the
mined tunnel, and the influence zone of the services
Fig 7a MRT tunnel underneath of mined tunnel
Fig Fig 7b,and 7 c shows the cross sections of the major services( MRT /Sewer lines and MRT viaduct ) .
Fig 7b- Section taken at Ch.. 0+055
Fig 7c-Section taken at Ch 0+065.
Fig 8 shows the general summary of utilities
encountered and the protection measures adopted.
Fig 8 . Utilities and protection measures adopted
The services and utilities and their allowable settlements
at the influence zones of the mined tunnel are indicted in
Table 2.
Table 2. Existing utilities within the area of mined tunnel
Utilities Protection
measures
Allowable
different settlement
Allowable
absolute settlement
The West
End line
viaduct
NA(Within
allowable limit) 15 or 1:1000 *
NA
CCL 4&
5 Tunnel
NA (Within
allowable limit 15 or
1:1000*
150 dia
water pipe
(Abandoned)
300 dia
water pipe
Re-propping
1:240
SingTel/
Star Hub cables
Re-propping
1:100
1650 dia
sewer
Within allowable limit
(estimated less than 1: 300)
1:300
230kv
cables
Support by
TAM Grouting
1:200
22kv
cables
Support by
TAM Grouting
Joint bays(4 m
above
Culvert)
Support and jack up
1:275 20
mm
*Whichever lesser , NA Not Applicable
Instrumentations were installed to measure the effect of
the works on them.
The mandatory requirements for the maintenance of
uninterrupted service for the services offered many
challenges to the project. At rare occasions when
settlements occasionally exceeded the suspension levels,
the pipe jacking and tunnel mining works were stopped
to enable lifting of the services to adjust the base
condition to normal to avoid damages to the utilities.
This is done in compliance of the approved( by the
authorities) stringent method. The laborious monitoring
process, with daily /weekly instrumentation meeting in
the presence of LTA, PUB and other agencies helped to
ensure that all such measures were carefully evaluated
and solutions decided upon expeditiously and promptly
carried out to prevent any further excessive settlements.
The requirements of Power Grid were particularly
strenuous on the joint cable bay at the centre of box
culvert along North Buona Vista Road, and cumulated
in the complex web of instrumentations installed (refer to
Fig 9 ).
Fig 9 . Layout of Joint Bay & Instrumentations
4.2.2 Pipe Jacking
Pipe jacking force for each pipe was calculated to be 50
tonne for the 53 m of jacking. This was mostly achieved
with the jacking force ranging from 50 to 80 tonne for
all except three rows of pipe that encountered
obstruction, which were unforeseen. These obstructions
were in the form of sheet pile, galvanised steel pieces and
timber residues, which were left in place by earlier
contracts. These had not identified during the tender
stage. The jacking force encountered for these cases went
up to over 150 tonne and additional time was needed to
complete these rows. However with skilled operators
and proper design and site management, no significant
damages were encountered in the works or utilities
during the process.
The particular case of encountering of sheet pile during
jacking proved to be very challenging indeed. Jacking for
this particular row progressed smoothly until the cutter
head of the machine hit very hard object, later found to
be sheet pile. A thorough investigation was carried, and it
was decided that a series of steel caisson of diameter
1.8 m were to be driven and the soil excavated , so as to
enable the cutting and the extraction of the sheet pile
for a number of locations. The works were carried out
overnight with partial lane closures to ensure minimal
traffic interruption along the North Buona Vista Road.
Luck does seem to play a big part as the sheet piles
were encountered only in one row of jacking.
The pipe jacking works were planned on a 24 hours
basis, alternating between actual pipe jacking and butt
welding of the steel pieces and testing of the welds,
which took over 4 hours for each joint. This resulted in a
cycle of 9 days in between each row of jacking. Two
jacking machines were utilised and the teams’ work to
jack the pipes in set predetermined designed sequence to
enable proper pipe roof to be formed after all pipes
have been jacked.
The three rows which hit obstructions - took much longer
(over 30 days each). In all, the jacking 22 pipes was
completed from Aug 2009 to Jul 2010, a total of 11
months. This is within the overall construction period
planned for the pipe jacking phase.
4.2.3 Settlement Control and Monitoring
The CIAR Report (Parsons B., 2010) helped to design
and adopt a comprehensive monitoring system as shown
in Fig 10 . This provided the systematic monitoring of
the ground settlement of the surrounding areas and other
changes such as in ground water table and other as a
result of construction of the pipe jacking and the mined
tunnel.
Fig 10. Layout of instrumentation and monitoring system
The allowable limits for settlement as set in CIAR are as follows:
• Alert level =0.7 x deisgn values
• Suspension level =deisgn value
The maximum settlement at the ground level was
expected to be along the centre of the mined tunnel
axis, at some 20 m from the jacking shaft. Fig 11 shows
the predicted settlement (Wong K S, 2009 ) along the
traverse section of 51mm, or maximum gradient of 1/250
or 0.4%. This was well within the LTA allowable limit of
1/100 (LTA 2009e).
Fig 11 The predicted settlement along the traverse
section during various stages of excavation
During construction, instrumentation monitoring
meetings with the contractor, specialists, sub contractors,
the instrumentation personnel, authorities (such as LTA,
Power Grid, SingTel, PUB) and consultants were held
daily / weekly accordingly to the needs. In the meetings,
the participants evaluated and decided on rectification
measures and adjustments to the procedures to ensure
working within the alert and suspensions levels and in a
safe and acceptable manner.
Plots in Fig 12 depict the readings taken with the prisms
installed to measure the combined effect of pipe roof and
mined tunnel. The prisms were installed along pipe L1
next to the lead pipe (The lead pipe is in the centre of the
top rows of pipes) which was expected to produce the
maximum settlements. The maximum settlement at this
pipe was 30 mm at about 20 m from the jacking shaft,
after the completion of the tunnel mining . This is below
the allowable of 125 mm , and predicated of 51 mm. At
two other prisms locations in the centre of the left and
right vertical pipes, maximum settlements were much
less than this figure.
Fig 12. Plots showing readings of Prisms installed along
the axis of pipe, after jacking and tunnel mining
5. SITE ORGANISATION AND MANAGEMENT
The contractor engaged a number of specialists and
subcontractors such as grouting, shaft construction , pipe
jacking, instrumentation and monitoring experts, as well
as experienced design consultants and supervision staff
to complete the design and build outlet drain . The well
coordinated efforts of these stakeholders resulted in
overall completion of the project with minimal time and
cost overrun.
During the course of the construction, the authorities
such as LTA and PUB are constantly on the scene to
provide the necessary monitoring and back up support,
and give prompt decision to enable problems to be
resolved.
Daily instrumentation meetings were troublesome but
useful to ensure all stakeholders are up to date and to
provide promptness of action.
In all, the project represents a successful implementation
of the good design and build construction mode for a
difficult and delicate project.
6. CONCLUSION
The pipe roof component of the contract C 8288 is the
most challenging of the project, and it was dictated at the
tender stage by the Client ( LTA) that it be done on a
design and build basis. Many stakeholders including the
client and other authorities such as PUB, Power Grid,
and SingTel etc were initially apprehensive on the risk
posed by such method. However with the direct and
active involvements of all parties, including designers,
and the accredited checkers, and with skilled
operations of the jacking and other specialists, the pipe
roof and the tunnel mining were done with uninterrupted
service of the bored tunnel, roads, sewer lines and
other utilities.
The strict procedures adopted on the work control
especially on monitoring and remedial measures taken to
contain settlement issues were strictly successfully
implemented. The tight control and reporting
requirements ensured that works were carried out within
safe and quality guidance, and within the project’s time
frame and contract cost approved. The lessons learnt
from this project, especially in mutual consultations and
control can be applied universally in similar projects.
ACKNOWLEDGMENT
The authors would like to thank the Contractor, Or Kim
Peow Contractors (Pte) Ltd (OKP) and Land Transport
Authority (LTA) for permission to publish this paper.
The views presented in the paper are solely that of the
authors, unless otherwise stated.
REFERENCES:
Atalah, A.L. and D.T. Iseley, 1991. "Pipe Arch
Horizontal Drift Method for MARTA's Transit Extension
Under I-285," Proceedings of Rapid Excavation and
Tunneling Conference, SME, Chapter 24, June, pp. 435-
453.
Darling, P., 1993. "Jacking Under Singapore's Busiest
Street,” Pacific Rim Supplement to Tunnels &
Tunnelling, summer, pp. 19-23. Jacking under
Singapore’s Busiest Street.
LTA 2009a, LTA interpretive soil report for C 8288.
LTA 2009b, Correspondence between OKP/LTA and
Authorities (LTA comments on contractor’s response to
LTA earlier comments on DAR 8288/CON/0019(DATED
7 May 09).
LTA 2009c ,LTA Civil Design Criteria
LTA 2009d ,Code of practice for RailWay Protecvtion.
LTA 2009e, Code of practice for works on Public Street.
Parsons Brinckerhoff, 2009, Design Report for Mined
Tunnel submitted to LTA.
Parsons Brinckerhoff, 2010, Report for overall
constriction Impact Assessment (CIAR).
Wong K S, O/ 2009, Independent report on Tanglin Halt
Outlet Drain-mined tunnel.