Jacking Pipe in Phoenix Soils - Government Engineering Journal

Jacking Pipe in
Phoenix Soils
Project is a first in the most significant upsize and maximum
drive length in the United States using the static pull
bursting method with replacement segmental pipe.
By Robert Webb and
Roger Olsen
P
hoenix has been experiencing
tremendous population growth
in recent years, as part of the
growing Southwest region of the
United States. This growth has taxed
some areas of its collection system.
Through recent sewer modeling updates
and the new Arizona Department of
Environmental Quality design requirements,
portions of the city’s wastewater
collection system were found to be at,
above, or nearing capacity. The addition
of the new infiltration and inflow design
requirements, coupled with the recent
population growth and the recent calibration
of its sewer model, indicated the
city’s collection system would require
immediate upgrades in many locations.
Phoenix developed the Sanitary
Sewer Relief and Replacement Program
to confront these issues. The potential
capacity deficiencies could impact new
Peoria Avenue Pipe Burst—15-in. to 18-in. vitrified clay pipe.
development upstream, which is an
important stimulus to the Phoenix
economy. Upsizing with full pipe
replacement, relief sewers, diversions,
and other techniques were considered as
solutions to this potential capacity deficiency.
The use of trenchless technologies
was approved by Phoenix as an
acceptable alternative approach to minimize
the impacts created by these construction
projects.
Phoenix decided to use a
Construction Manager at Risk
(CM@R) delivery method to tackle this
enormous undertaking. Project
Engineering Consultants (PEC,
www.pecaz.com) was one of eight engineering
firms selected for this program.
In particular, PEC was assigned a relief
sewer project in the area of 35th Avenue
and Peoria Avenue in Phoenix. PEC
worked closely with Kiewit Western
Company (CM@R contractor) from the
30 percent phase of the design to develop
an innovative approach to increase
the capacity deficiencies with minimal
socio-economic impact. The goal was to
consider alternatives that would minimize
conventional open-cut construction
headaches such as impeding traffic,
impacting local business and customers
and to ultimately render a less costly
solution. Pipe bursting was determined
to fulfill the need for upsizing these
capacity deficient pipes without open
trenching their streets. Kiewit submitted
a final guaranteed maximum price of
$5.3 million for pipe bursting, which
fell well below the open-cut cost model
for the project—about $7.9 million.
Project Details
The project consisted of an unprecedented
upsizing of nearly 7,400 ft of
existing 12- and 15-in. pipe, which are
ten to 20 ft deep under major streets
with the usual multitude of existing utilities.
The sewer layout consisted of two
main lines perpendicular to each other
that intersected at Peoria Avenue and
35th Avenue. The 2,500 ft along Peoria
sewer main was an existing 15-in. vitrified
clay pipe (VCP) to be upsized to
18-in. diameter. The 4,700 ft along
35th Avenue sewer main was for the
most part an existing 12-in. VCP pipe
to be double upsized for most of its
length to an 18-in. diameter. The
method of pipe burst selected was static
pull with “cartridge” loading using segmented
jacking pipe.
This method of pipe bursting kept
the jobsite footprint relatively small and
compact. Utilizing segmented pipe
eliminates the need for a long lay-down
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Grundoburst 2500G (top) and extraction
cage (bottom) in receiving pit.
area on the project site as would be
required with welded pipe. This is highly
beneficial in high-traffic urban settings
as long strings of welded pipe
would have inhibited traffic flow and
driveway access before and during the
bursting operation. Consequently, traffic
control did not become a major issue
for this project during the pipe bursting
operation.
Launch and receiving pits were constructed
at new manhole locations at
about 400-ft intervals. Trench boxes
were used to stabilize the walls of the
pits and provide a safe working environment
allowing ample room for equipment
and pipe. The bursting equipment
could easily be rotated 180-degrees in
the launching pit to begin bursting pipe
from the opposite direction.
Pipe bursting requires the flow in the
existing pipe to be bypassed or diverted
out of the pipe. The existing pipe was
cleaned and closed-circuit television
inspected to ensure there were no severe
alignment problems, sags, and to locate
all service laterals before installation of
new pipe. Existing service laterals were
intercepted, monitored during the operation,
and connected into the sewer
bypass system, which ran above and
alongside the pipe bursting operation.
The bypass piping was conveniently tied
to the sewer system far downstream
from all the operations. When a driveway
was encountered, the bypass piping
was trenched under and paved to allow
property owners full access at all times.
The project also included a 200-ft
jack-and-bore portion through the high
traffic volume intersection of 35th
Avenue and Peoria Avenue. The CM@R
used a local subcontractor to perform
that operation. It entailed a setup that
installed a 36-in. OD, 3/8-in. thick steel
casing diagonally across the intersection
from the traffic island in Peoria Avenue
northeast to the sidewalk in 35th
Avenue. 180 linear ft of 18-in. bell-andspigot
VCP was jacked into the new casing.
The jack-and-bore took about 3.5
weeks to complete. An additional two to
three days was added to the jack-andbore
schedule because part of the tunnel
had to be hand mined.
All the utilities in the pipe zone were
identified in the plans and marked by
the respective Arizona Call Center “Blue
Stake.” Some of these included fiber
optics conduits and electric duct banks,
which were potholed and surveyed,
waterlines, telephone conduits, natural
gas lines, storm drain connectors, and
sewer lines. During initial construction
in one portion of the alignment, problems
were encountered with an existing
40-year old six-in. water main composed
of asbestos cement pipe (ACP),
which meandered adjacent to the sewer
alignment. The ACP water main began
breaking at multiple locations apparently
due to pipe movement caused from
soil displacement during the pipe bursting
operation. The city decided to relocate
the entire portion of the ACP
waterline, which was within six ft of the
existing sewer pipe.
The decision to relocate
this existing
water line would have
been the same if an
open-cut construction
method was
elected over pipe
bursting. There were
no other major conflicts
with utilities
and no service disruptions
during construction.
The utilities
that ended up in
the pit areas were
supported and maintained
at all times.
Potholing of electrical utilities was
performed during design. In addition to
potholing, soil borings were collected
every 150 to 200 ft along the project for
a total of 19 soil borings. Soil boring
data is important for pipe bursting and
jack-and-bore projects to determine feasibility.
Soil classification, size, and density
are particularly important.
Bursting Challenges
Generally, the pipe bursting went
smoothly, which was commendable, due
to conditions that had to be overcome.
The Peoria Avenue section had the most
challenges due to the original pipe
installation and existing trench configurations.
There were three locations along
Peoria Avenue that required excavation.
The equipment operator could usually
determine when harder conditions were
encountered by the sound of the bursting
unit’s power pack. Excessive
hydraulic pressures usually indicated the
presence of an obstruction. It was more
economical for the contractor to continue
the pipe burst and avoid open-cut
due to higher production rates with pipe
bursting. One obstruction proved to be
non-compressible backfill (cementitious
cap) or an existing point repair. The
cementitious cap appeared to be low
strength because the bursting operation
pulled through much of it. When difficult
ground conditions caused hydraulic
pressures to exceed the working limits of
the machine, it was mutually decided to
open-cut those portions. The bursting
head was excavated and a portion was
24-in. OD expander followed by the new 18-in. VCP jacking
pipe on arrival into the receiving pit.
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hand laid for a short distance until the
ground conditions improved allowing
bursting operations to resume.
In isolated cases, the original pipe was
laid closer to one side of the original
trench wall and not the centerline of the
trench. The original trench wall was
more unyielding than the bedding and
backfill materials and would not accept
the necessary compaction required by
the pipe bursting process as readily as
the bedding and backfill material. These
obstacles increased pulling tensions
above the equipment’s safe working limits.
In these situations, the bursting head
was excavated and pipe was hand laid
until conditions improved. If additional
information about the trench geometry,
pipe location, and other obstructions
would have been available, shafts might
have been relocated resulting in a different
pipe bursting strategy.
40-ton cylinder pack.
The contractor’s second pull at 35th
Avenue exceeded all expectations. After
the first pull of about 98 ft, the machine
was relocated downstream and the
longest burst of 448 ft was accomplished
with only minor issues. There were
some areas where minor heaving was
observed because the existing bottom of
the pipe was about ten ft deep. Minor
cracks occurred in paved areas where the
access streets were to be repaired anyway.
A portion of sidewalk rose around
a bus bay, which was easily repaired.
Other than these few locations, no other
locations of heave were observed.
A portion of the upstream pipe rose a
few inches during the initial pull back
and the contractor adjusted those few
pipe sections before reinstalling a new
manhole in the launching pit. This was
the longest attempt using this method
of pipe bursting, which was an encouraging
turn for the project and helped
calm some of the jitters. The pull back
was completed in only a few hours.
Initially, the project schedule was
delayed due to record summer rainfalls
during the “monsoon” season in the valley.
Rain also delayed the project for two
to three days during the winter rainy
season in December. Rain delays were
mainly due to pit flooding.
Bursting Equipment Setup
The static pipe bursting equipment,
provided by TT Technologies Inc.
(www.tttechnologies.com), included a
Grundoburst® 2500G static bursting
machine and the accompanying tooling.
This machine can pull up to 315 tons. It
would prove necessary to use virtually
all of the machine’s capacity in the difficult
soil conditions encountered on the
project. The Grundoburst 2500G
machine utilizes Quicklock rods
between the machine and the expander
that weigh about 400 lb each. These
rods were connected to a special 22-in.
OD expander sized for the new 18-in.
VCP. The expander had a special internal
socket arrangement for the lead
piece of VCP to butt against. To add
new sections of pipe as the pull progressed,
additional rods were added followed
by the pipe sections, which were
slipped over the rods. The cylinder pack
with three pressure plates was then
employed and pinned to the rods. Next,
the plate was hydraulically energized to
serve two functions: 1) push the newly
added pipe joint fully “home,” and 2)
hold the entire jacking pipe train in
compression as the pipe bursting
expander was pulled forward.
The bursting equipment for this project
was designed and assembled for the
specific purpose of bursting the existing
VCP and towing in the new nonrestrained
joint jacking VCP. A ride
along hydrostatic machine attached to
bursting rods inside the new pipe sections
kept the column of assembled pipe
segments in compression as the bursting
progressed. The pipe sections were lowered
into the pit and the pipe joints were
pushed home with the cylinder pack via
a pressure plate. The cylinder pack provided
40 tons of force to keep the assembled
pipe segments in compression (and
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ods in tension) as the bursting head is
pulled toward the Grundoburst static
pipe bursting machine. The cylinder
pack was sized according to the pipe
manufacturers’ specification for the
weight of each 18-in. diameter pipe section.
For example, in a 400-linear ft (lf)
run: 133 lb/lf x 400 lf=53,200 lb 27
tons), which is well within the limits of
the cylinder pack’s 40-ton capacity. As
the bursting head is pulled forward fracturing
the existing VCP and expanding
the fragments into the surrounding
backfill, the rear cylinder pack pressure
plate keeps the assembled pipe sections
in compression.
The contractor’s team kept in constant
telephone/radio communication
and the hydrostatic pressures were
observed and recorded real-time during
the bursting operation. To absorb these
pressures, a chipboard compression ring
was installed between each pipe joint to
distribute the axial load transferred from
one pipe section to another. Cycle times
for each section of pipe to be assembled
and pulled forward during bursting
began at an average rate of 1/2 ft per
minute. As the project progressed, the
crew became much more efficient
resulting in average rate of one ft per
minute. Thus, a typical 350-ft reach was
completed in 5 1/2 to six hours.
Product Pipe
NO-DIG® vitrified clay jacking pipe
(Mission Clay Products, www.missionclay.com)
was used as the replacement
pipe material on the project. This gravity
flow sewer pipe has been used for
slurry microtunneling (MTBM), pilot
tube microtunneling (GBM), sliplining
steel casing, and now static pull pipe
bursting. The vitrification process produces
a material with average compressive
strength of 18,000 psi. The jacking
pipes are manufactured with a precision
ground joint; a Polyisoprene, EPDM, or
Nitrile elastomer compression gasket;
and a Series 316 stainless steel collar at
each pipe joint.
The standard 6 1/2-ft length of 18-in.
NO-DIG pipe utilizes a single fin elastomer
compression gasket with 4 3/4-in.
wide, 16-gauge, 0.06-in. thick stainless
steel collars at each joint. It was decided
on this project, due to the strain on the
The first pipe section on each bursting run was fitted with a lubricant port and a
“Witches Hat” check valve (inset) to reduce frictional pulling forces.
pipe joint during the installation
process, to use a double fin elastomer
gasket with a five-in. wide, 13-gauge,
0.09-in. stainless steel collar. This double
finned joint with the heavier steel
collar is the standard in pipe diameters
24-in. and up.
The first pipe section on each bursting
run, a three-ft sacrificial piece
behind the expander, was fitted with a
lubricant port to reduce frictional
pulling forces (pipe drag). This three-ft
section placed the first “pivoting and
flexible” joint just outside the rear of the
expander to allow movement as opposed
to having a full 6 1/2-ft pipe section. To
manufacture the lube port the factory
cored a 2 1/4-in. hole in the pipe barrel
for a 1 1/2-in. National Pipe Thread
(NPT) threaded coupling, attached
using ceramic epoxy, to accept a 1 1/2-
in. NPT “Witches Hat”" one way check
valve. Microtunneling Inc. (www.microtunneling.com)
supplied these check
valves for the project.
Conclusion
Production rates were affected by
unknown conditions such as a cementitious
cap, dry dense soil conditions adjacent
to the existing trench, and the
existing sewer pipe alignments. Another
production delay originated when the
contractor opted to open-cut in lieu of
pipe busting at one location. On the
other hand, at two locations, open-cut
was specified on the plans to correct
reverse slopes and the contractor
obtained approval to pipe burst at these
locations. Not all of the construction
delays can be attributed to this lack of
information. However, if more information
about the original trench geometry
were known ahead of construction,
unexpected delays in production could
have been minimized.
Pipe production via pipe bursting
exceeded everyone’s expectations. The
project took nine months to complete
the pipe bursting and jack-and-bore
activities. The contractor estimated that
the project would have taken at least 12
months to complete if it had been opencut.
In addition to the construction
duration savings, the project accomplished
a maximum drive length of 448
ft. This is the longest length of jacking
VCP to be installed via pipe bursting in
the United States. In addition, the project
was the first in the United States to
perform a double upsize pipe burst
using jacking VCP.
GE
Mr. Webb is Water and Wastewater Director,
Project Engineering Consultants, Ltd. Mr.
Olsen is Construction Manager, City of
Phoenix, Water Services Department,
Phoenix, AZ.
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