North American Special - Trenchless International

north america
April 2009 - Trenchless International
HRX: heading across the harbour
A record was recently set on the Virginia Natural Gas Hampton Roads Crossing (HRX) HDD bore.
Project Manager Les Flora spoke with Trenchless International about the innovative and challenging
project.
The aim of the project is to support
distribution company Virginia Natural Gas
(VNG), a subsidiary of AGL resources.
The project itself comprises 21 miles
of 24 inch diameter pipeline, extending
transmission gas facilities under Hampton
Roads Harbour, Virginia. The harbour is
one of the largest natural harbours in the
world. The harbour is also home to the
largest naval base in the world and has
a significantly high degree of commercial
maritime traffic. The crossing of the harbour
itself includes four miles of pipeline
from Newport News to Newport News.
In addition the project involves an
HDD crossing of the Elizabeth River.
This crossing demanded a 7,300 feet
(2,225 metres) HDD drive in 24 inch pipeline
– a bore record.
Project Scope
Currently, the VNG distribution system is
divided into two non-contiguous pipeline
systems – southern and northern – due
to the geography of the Hampton Roads
harbour. On a peak day, each system is
fed by a single gas supplier; Columbia
Gas Transmission in the Southern system
and Dominion Transmission in the
Northern system, making them vulnerable
to gas disruptions. This project will ensure
reliability of supply and future availability.
The project includes the construction
of approximately three miles of onshore
pipeline in Hampton, four miles of onshore
pipeline in Newport News, four miles of
onshore pipeline in Norfolk, and ten miles
crossing the Hampton Roads Harbour.
The project will also include upstream
pipeline compression facilities in Hanover
and Charles City Counties, and a city
gate station at the termination point in
Norfolk.
Design and construction
The marine construction project team
included Weeks Marine, Mears Horizontal
Directional Drilling and Bradford
Brothers.
Weeks Marine is the general contractor
on the marine portion, providing all of
the marine equipment and diver support.
Mears and Weeks teamed up to complete
the HDD with their pipeline subcontractor,
Bradford Brothers.
Crossing the harbour
The harbour crossing consists of five
separate HDDs ranging in length from
3,000 – 3,800 feet.
Mr Flora said that Trenchless
Technology was selected for a number
of reasons. The two main drivers were
the environmental permits and the US
Army Corps permits required as the pipe
path bisected an anchorage area.
The Marine Resources Commission
is very active in protecting the area.
Alternative methods such as conventional
dredging, laying pipe on the bottom
or even jetting it in were considered.
However, Mr Flora said that “because of
the environmental impacts, or I should
say, perceived environmental impacts,
the Marine Resources Commission would
not permit it. So we had to directionally
drill under their biggest area of concern.
“On the Army Corp side there is
approximately 5,000 feet of pipe to go
under an anchorage area. The anchorage
space is so valuable to the maritime
community that the decision was made
to directionally drill this section of the
pipeline.”
Finally, a natural shipping channel is
also a part of this crossing. Mr Flora said
that the company was aware that this
section would be directionally drilled in
order to reach the depth that would be
required under the channel.
The depth of the channel is 15 metres
with a design depth of 19 metres. The
drill path was required to be a minimum
of 6 metres under the design
depth. Therefore the shipping channel
drill was approximately 25 metres below
the water.
Mr Flora continued “Three of [the
drives] are marine to marine drills so
we’re drilling from a barge and the
receiving rig is on another barge.
“We’re building those pipe sections
out on the end of Craney Island, which
is basically a beach, out into the harbour
and then towing those sections by tying
them to tug boats. Towing them off the
end of the island and floating them into
place and then sinking them and then
hooking them back to the drill rigs for
the pull back.”
Mr Flora said there is also another area
requiring trenchless expertise. “We are
doing a bunch of small directional drills,
on the Upland piece of this project. We
have 7 miles (11.2 km) of pipe on land
in Newport news, and about 4 miles (6.4
km) in Norfolk. They are very heavily
urban quarters, there are just not a lot of
good places to put pipe, much less 24
inch pipe.”
For example, for the first mile onshore
of Newport News, the pipe was directionally
drilled under a tidal wetland creek as
there was not a less congested route for
the pipe. This pipe was separated into
two drills, each approximately 2,800 feet
(853 metres). Mr Flora said that space
was incredibly tight, “the pipe looked
like a pretzel wrapped around a tree.”
Mr Flora said that without Trenchless
Technology the sections directionally
drilled, in most cases, could not have
been completed in an alternative method
in a cost effective way.
A challenging crossing
The Elizabeth River crossing was one
of the most ambitious and challenging
parts of the project as this demanded
the laying out of a string of pipe 7,300
ft long.
Fortunately Craney island, a government
owned area, is located right in
the middle of the project. The island
is a US Army Corps dredge disposal
management area. The contractors had
to share the very small island area with
Army Corp Engineers and the associated
traffic.
Mr Flora explained that the Dominion
University is located on the other side of
the river where the pipe was to be pulled
back. During the semester this area is
filled with approximately 24,000 students.
Therefore the team could only operate
from 12 May until 20 August.
Elizabeth River Crossing: pullback.
Elizabeth River Crossing.
Harbour Crossing: pull head with
hose connections for pipe flooding.
Elizabeth River Crossing: pullback.
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April 2009 - Trenchless International
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