Horizontal Directional Drilling

HORIZONTAL
DIRECTIONAL DRILLING
INTRODUCTION
EN Engineering has designed hundreds of
Horizontal Directional Drilling (HDD) crossings and
is an industry leader in the identification, planning,
design, and support during installation of HDDs.
The use of HDD in the pipeline industry began
in the 1960s and was fully established by the
1980s as a way to install pipelines while utilizing
trenchless technology with minimal impact to the
feature being crossed. These features, including
roads, railroads, waterbodies (rivers, streams, and
wetlands) or other environmentally or culturally
significant areas are typically sensitive in nature
and cannot be disturbed by conventional open
trench construction methods.
PRELIMINARY ACTIVITIES
Whether part of a larger overall pipeline installation
or a stand-alone maintenance/replacement
project, EN Engineering completes a preliminary
front-end assessment of all HDD crossings. Due
to the potential risk and cost associated with
an HDD, the assessment checks to see if other
construction techniques (including open cutting
and conventional boring) can be utilized instead.
If it is determined that because of construction,
permitting, or other issues a conventional crossing
technique is not feasible, our team will begin its
HDD planning process.
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Utilizing maps, drawings, aerial photography,
elevation data, and other technology, we will develop
possible HDD alignments, workspace layouts
(including pipe pull back), entry and exit points,
considerations for drilling mud management, and
a preliminary plan and profile. Once this desktop
analysis is done, we typically conduct a site visit to
confirm actual site conditions support this preliminary
design and adjust it as necessary.
GEOTECHNICAL SURVEY
Based on the location and complexity of the HDD,
EN Engineering determines the quantity, locations,
and depths of exploratory soil bores needed to
complete the detailed design of the HDD crossing.
These borings show the depth of the water table and
identify soil and rock properties. A hydraulic fracture
analysis may be performed using geotechnical data
to minimize the risk of inadvertent mud release
during the drill. This analysis is sometimes required
by the governing permitting and/or regulatory agency
and uses the Delft equation as described in the
“Guidelines for Installation of Utilities Beneath Corps
of Engineers Levees Using Horizontal Directional
Drilling” USACE, 2002. EN Engineering partners
with geotechnical service firms that can complete the
geotechnical field investigations, laboratory testing,
and associated reports we needs to complete the
HDD design.
SURVEY
EN Engineering will coordinate a topographic
survey of the proposed project area based on the
recommended alignment for the final engineering
design effort. In addition, a boundary survey can
be performed to accurately identify the property
owners affected by the project. If required, property
plats can be developed for land negotiations. EN
Engineering also provides the survey support to
assist the construction contractor and to capture
any as-built information. We maintain relationships
with established survey firms that can complete the
required design, boundary, pre-construction staking,
and as-built survey activities.
DETAILED DESIGN
Next, EN Engineering will advance the preliminary
engineering for the HDD through the detailed design
phase. This includes determining the appropriate
drill path to ensure that bending, pullback, and
testing stresses are within industry standards. For
challenging or unique crossings, we can have
layouts for each HDD location and workspace
reviewed by a reputable HDD contractor to ensure
that constructability is optimized.
EN Engineering utilizes the Pipeline Research
Council International (PRCI) guidelines in its design
of HDDs, which involves modeling the drilled path to
define its shape and properties during installation.
Utilizing these guidelines, we develop a design that
governs pipe specifications (wall thickness, grade,
and corresponding D/t ratio), depth of drill, entry/exit
angles, radius of curvature and tangents, and
overall drill length. Based on the pipe specifications,
operating pressures, and site elevations, we can
develop pre- and post-installation hydrostatic
testing parameters. Our team will also develop a
detailed material list (primarily pipe and coating),
identify qualified vendors, develop bid packages,
analyze quotations, and cut requisitions as needed,
with purchase orders typically issued on client’s
letterhead.
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PERMITTING AND RIGHT-OF-WAY
SUPPORT
When requested, EN Engineering provides the
drawings, exhibits, data tables, and other information
required in support of the permitting process. Our
team understands the permitting process as it relates
to the Federal Energy Regulatory Commission
(FERC), the US Army Corps of Engineers (USACE),
US Fish and Wildlife Service (USFWS), and other
state and local agencies related to environmental,
historic preservation, and non-environmental permits.
We can also provide exhibits, sketches, and plats
needed for the acquisition of both temporary and
permanent easements for the construction and
operation of the installed HDD crossing. Using a
subcontracted land services company or the client’s
internal land department, we can investigate current
ownership of all affected properties the project may
encroach on where amended or new easements may
be required. This investigation includes the study of
tax maps, property deed records, and similar sources
of information.
CONSTRUCTION SUPPORT
EN Engineering provides support related to the
construction bid phase, including the identification
of qualified contractors, development of a scope of
work and overall bid package, responding to RFIs,
and selection of a construction contractor. We can
also help with the pre-bid meeting, the associated
job site review, and staking of the final route and
workspace layout for the bidders.
We also review the HDD design and drilling plan with
the awarded contractor to determine if the method
and equipment meet the project’s requirements.
Risk mitigation strategies may be implemented at
this time, including but not limited to: increasing
the annular space during the pilot hole, decreasing
drilling fluid density and/or fluid pump rate,
specifying mud additives to maintain tunnel stability,
or lowering the alignment.
When requested, EN Engineering can review the drill
pilot-hole profile prior to pullback of the pipe string
in order to determine if the drill alignment/geometry
appears to be acceptable and the pipe will not be
overstressed. We can review the pilot-hole drill data
daily in order to monitor the progress and ensure the
drill is being installed per the design plan.
Our team can provide an as-built plan and profile
and pipe joint/weld map, utilizing information from the
HDD contractor, including the X, Y, Z location (or the
azimuth/inclination and distance) of each drill string
joint. We will record the entry and exit points for the
pilot-hole drill string and any exposed drill string joint
ends, and capture the top centerline of pipe along
the portion of the pipeline from the tie in points to the
entry and exit points of the HDD.
POST-CONSTRUCTION
Upon completion of the HDD, EN Engineering can
assemble and provide a project completion package,
consisting of the as-built drawings, boring logs,
design calculations, material test reports (MTRs) and
other documents necessary to meet the client/owner
recordkeeping requirements.
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