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Pipelines 2019
141
Risk Identification for Pipeline Installation by Horizontal Directional Drilling (HDD)
Amir Tabesh, Ph.D.1; Mohammad Najafi, Ph.D., P.E., F.ASCE 2; Zahra Kohankar3;
Mohammadreza Malek Mohammadi4 ; and Taha Ashoori, Ph.D., P.E.5
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1
Design Engineer, DAL-TECH Engineering, Inc., 17400 Dallas Pkwy., Suite 110, Dallas, TX
75287. E-mail: [email protected]
2
Professor and Director, Univ. of Texas at Arlington/CUIRE, PO Box 19308, Arlington, TX
76019. E-mail: [email protected]
3
Graduate Teaching Assistant, Univ. of Texas at Arlington/CUIRE, PO Box 19308, Arlington,
TX 76019. E-mail: [email protected]
4
Graduate Teaching Assistant, Univ. of Texas at Arlington/CUIRE, PO Box 19308, Arlington,
TX 76019. E-mail: [email protected]
5
Geotechnical Engineer, EnTech Engineering PC, 1265 Synergy, Irvine, CA 92614. E-mail:
[email protected]
ABSTRACT
Horizontal directional drilling (HDD) has become a favorable method of pipeline installation
in urban areas and for crossing obstacles such as rivers and roads. HDD is defined as a steerable
system for the installation of pipes, conduits, and cables in a shallow arc using a surfacebalanced drilling rig. Due to work being done underground blindly, it is important to conduct a
risk evaluation prior to actual construction. The primary steps to address risk assessment are risk
identification and risk log documentation. The objective of risk identification is to understand
what is at risk within the context of the project’s explicit and implicit objectives and to generate
a comprehensive inventory of risks based on the threats and events that might prevent, degrade,
delay, or enhance the achievement of project objectives. This necessitates the development of
risk identification guidelines to ensure that contractors monitor the most probable risk and
manage its positive and negative impacts effectively and efficiently. This paper presents a
comprehensive risk identification process for HDD method, by dividing risks into four
categories: drilling fluid, soil, equipment and pipe, and operation and management to help
project managers to have comprehensive checklist for their response strategy plan.
Key words: Horizontal Directional Drilling, HDD, Risk Assessment, Risk Identification,
Risk Analysis, Trenchless Technology
INTRODUCTION
Horizontal directional drilling (HDD) technology originated from the oil fields in the 1970s
and was evolved by merging technologies used in utilities and water well industries (Najafi and
Gokhale, 2005). HDD, one of the most common trenchless installation methods, is a steerable
system used for the installation of pressure pipelines, cables and conduits in a shallow arc using a
surface-launched drilling rig (Najafi, 2013).
Traditionally, HDD was used in large-scale crossings such as rivers in which a fluid-filled
pilot bore is drilled without rotating the drill string, and this is then enlarged by a wash over pipe
and back reamer to the size required for the product pipe (Najafi and Gokhale, 2005). However,
today HDD has become a very versatile technique utilized for installing 2-in. conduits under
streets and driveways, as well as 60-in. casings under rivers, dams, and levees. Although
trenchless installation methods significantly reduce the negative impacts of open-cut trenching to
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quality of life and reduce damage to pavements, and surrounding infrastructure, there are some
potential effects that should be understood (Najafi, 2010; Tabesh et al, 2017). Table 1 shows
three different type of HDD with diameter range.
Table 1. Main Characteristics of HDD Methods (Najafi, 2010)
Method
Diameter
Maximum
Depth (ft)
Typical Application
Rage (in.) Installation (ft)
Small (mini)
Telecom, Power Conduits,
2-12
Less than 600
Less than 15
HDD
and Gas Pipeline
Medium
Between 600
Between 15
12-24
Pressure Pipeline
(midi) HDD
and 900
and 75
Large
Between 900
24-60
Less than 200 Pressure Pipeline
(maxi) HDD
and 10,000
It is important to pay close attention to the project surroundings (surface and subsurface
conditions) to identify unfavorable conditions and possibilities. The risk conditions require extra
attention in order to ensure the safety of the construction personnel and public, as well as
surrounding facilities and infrastructure. Most underground and pipeline construction projects
entail some risks due to unknown subsurface conditions (Najafi, 2010).
Risk identification and analysis are the critical steps in any risk management process. The
outcome of a risk analysis is the estimation of the probability of occurrence and impact of
different risk events. The objective of this study is to identify, summarize and classify a series of
HDD construction risks that have significant impacts within the industry.
Many stakeholders and contractors who perform the installation of pipes by HDD are not
fully professional in risk assessment and are not able to provide the project with a risk
management plan during either designing phase or construction. The contractors emphasize the
necessity of risk assessment before starting the realization of the investment, as the estimation of
the risk level is the starting point to analyze the project feasibility and cost estimation (Gierczak,
2014). By identifying and quantifying HDD risks, not only better information will be available to
support decision makers in setting project objectives, but also many serious and high impact
risks regarding to the HDD failures can be avoided. The industry would also be in a better
position to develop risk response strategies further improving performance.
HORIZONTAL DIRECTIONAL DRILLING PROCESS
Horizontal Directional Drilling process is completed in two main stages which are followed;
1. Preconstruction Process
2. Installation Process
a) Pilot Hole
b) Pre-reaming
c) Pull Back Operation
Preconstruction Process: At preconstruction process, a design plan and profile drawing
must be prepared for each crossing. Then, site preparation is performed by setting up drilling rig
at the proper location and preparing slurry to stabilize and lubricate the borehole. On the other
side of the proposed alignment, pipeline, reamer, and storage space that are required for prereaming and pullback are prepared.
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Figure 1. Horizontal Directional Drilling (HDD) construction procedure (Platosh, 2010)
Pilot Hole: The first stage of an HDD installation is to advance a small diameter pilot hole
along the designed path with a drill bit attached at the front of a drill pipe string. Drilling the
pilot hole is the most important phase of an HDD project, because it determines the ultimate
position of the installed pipe (Najafi and Gokhale, 2005). A small-diameter (typically 1 to 5 in)
drilling string penetrates the ground at the prescribed entry point at a predetermined angle. The
leading assembly used for steering, survey and advancing the drill bit is called the Bottom Hole
Assembly (BHA) and consists of the drill bit, a bent sub or mud motor, non-magnetic drill collar
and downhole survey probe.
The slight bend in the bent sub or mud motor provides a steering bias that can be oriented in
the desired direction of advancement to allow the pilot hole to be advanced according to the
designed alignment and profile (Miller & Sayem, 2016). The drill path is monitored by a special
electronic tracking system housed in the pilot drill string near the cutting head (Kohankar et al,
2017).
Pre-reaming: Once the pilot hole is advanced along the desired path and the drill bit exits
the ground at the exit point, the BHA is then removed from the downhole drill pipe string and
replaced with a larger diameter reaming tool to enlarge the pilot hole. This stage of
reaming/enlarging the pilot hole may be completed in several stages depending on the final
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diameter required to install the pipeline. The reaming tool typically consists of a circular array of
cutters and drilling fluid jets tailored to the anticipated subsurface conditions (Miller & Sayem,
2016). In general, for mini HDD, the final size of the bore should be at least 50% larger than the
outside diameter (OD) of the product pipe (Najafi and Gokhale, 2005). This overcut is necessary
to allow for an annular void for the return of drilling fluids and spoils and to allow for the bend
radius of the pipeline (Najafi and Gokhale, 2005; Kohankar et al, 2017).
Pull Back Operation: After the hole has been reamed to the targeted diameter, the hole is
typically swabbed (one or more times) with a reaming tool to check the hole condition prior to
pullback operations. Following the swab pass, the product pipe, which is prefabricated, tested,
supported by rollers and pipe handling equipment at pipe side, is attached to a pullback
assembly. The pullback assembly typically includes a pull head, reaming tool, and swivel. A
reamer is located between the pull head and the drill string to ensure that the hole remains open
and to allow lubricating fluid to be pumped into the hole during the pullback (Kohankar et al,
2017).
RISK ASSESSMENT
Risk management is an important part of the decision-making process in construction
(Kangari, 1995), and now widely accepted as a vital tool in the management of projects (Wood
& Ellis, 2003). The ultimate purpose of developing these risk management techniques is to add
value to project delivery and improve efficiency of the construction industry during practice.
Thus, there has been an increase in research aimed at investigating risk management practice in
the construction industry (wood & Ellis, 2003; Kohankar et al., 2017). In general, the risk
management process for a project includes the following steps (see Figure 2). The focus of this
study is to identify risks during pipeline installation by HDD method.
Figure 2. Risk Assessment Process
RISK IDENTIFICATION
Risk identification is a deliberate and systematic effort to identify and document the project’s
key risks. The objective of risk identification is to understand what is at risk within the context of
the project’s objectives and to generate a comprehensive inventory of risks based on the threats
and events that might prevent, degrade, delay or enhance the achievement of the objectives. This
necessitated the development of risk identification guidelines to ensure that owners manage risk
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effectively and efficiently (Kohankar et al., 2017).
Comprehensive identification and recording of risks are critical, because a risk that is not
identified at this stage may be excluded from further analysis. In order to manage risks
effectively, project managers (PMs) should know what risks they are faced with. The risk
identification process should cover all risks, regardless of whether such risks are within the direct
control. Contractors should adopt a rigorous and on-going process of risk identification that also
includes mechanisms to identify new and emerging risks timeously. Risk identification should be
inclusive, not overly rely on the inputs of a few senior officials and should also draw as much as
possible on unbiased independent sources, including the perspectives of important stakeholders
(Kohankar et al., 2017).
RISK IDENTIFICATION AT HDD DURING CONSTRUCTION
For this study, different risk identification methods such as brainstorming, checklist,
document review, and interview conducted to identify four main risks, which are followed;
Drilling Fluid: Drilling fluid plays an important role in the directional drilling operation and
is utilized for all stages of the HDD operation. Drilling fluid is primarily composed of bentonite
clay mixed with water, polymers and other additives (Ariaratnam & Beljan, 2005). Drilling fluid
is composed of a carrier fluid (water) and fluid additives (bentonite and/or polymers). Bentonite
is a naturally occurring clay mineral that forms a mud when mixed with water. When bentonite is
mined, the clay platelets (flat plate-like particles), which are subjected to high confining stresses,
are closely compressed with little water between layers. An “aggregate” is a unit of stacked clay
platelets. When water enters between some of the clay platelets, it immediately causes them to
disperse.
The use of drilling fluid is a critical part of the drilling technique, since it plays a key role in
the pipeline installation by HDD method. The principal functions of drilling fluids are followed
(Ariaratnam & Beljan, 2005);
a) Moving drill spoil to the surface by suspending and carrying them in the fluid stream
flowing in the annulus between the drilled bore wall and the drill pipe or product pipe.
b) Cleaning the buildup of soil on drill bits or reamer cutters by directing fluid streams at the
cutters.
c) Cooling the downhole tools and electronic equipment.
d) Lubricating to reduce the friction between the drill pipe or product pipe and the bore wall.
e) Stabilizing the bore, especially in loose or soft soils, by building a low permeability filter
cake, and exerting a positive net hydrostatic pressure against the bore wall. The filter
cake along with positive hydrostatic pressure reduces the chance of collapse of the bore
and prevents formation fluids from flowing into the bore or drilling fluids from exiting
the bore into the formation.
f) Providing hydraulic power to downhole tools such as mud motors.
In order to suspend the drilled spoil, which consisting of excavated soil or rock cuttings, high
gel strength of the drilling fluid is needed. It will raise the viscosity of drilling fluid. In order to
carry the drilled spoil out of the borehole under low pressure, low viscosity of drilling fluid is
needed. Balance of this contradiction is an art, especially in gravel or cobble strata. It is hard for
drilling fluids to suspend and transport cuttings out of the borehole completely, so stuck pipe
often occurs, requiring more bentonite and additives to be added. Without protective measures,
drilling in such geologies becomes a risk (Lu et al. 2013).
Below is identified risks, which are related to drilling fluid.Bypass Failure
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 Filtration Control Failure
 Fluid Loss
 Fluid Seepage
 High Density Fluid
 High Level of Calcium at Fluid
 Hydrofracture
 Improper Amount and Quality Bentonite, Polymer, and Additives
 Improper Filtration Characteristics
 Improper Fluid Conductivity and Disposal
 Improper Fluid pH
 Improper Fluid Viscosity and Yield Point
 Improper pH and Quality of WaterImproper Rheometer
 Inadequate Amount of Fluid
 Inadequate Annular Pressure
 Inadequate Fluid Lubricity
 Insufficient Depth of Installation
 Insufficient Pumping Pressure
 Loss of Circulation
 Loss of Depth and Floating Line
 Low Fluid Hardness
 Low Fluid Pressure and Pumping Rate
 Low Fluid Suspension Capability
 Low Gel Strength
 Mud Cleaning System Failure
 Solids Control work Failure
 Unsuitable Recycled Fluid
 Vacuum Failure
Soil: Ground conditions (i.e., soil and rock conditions) can create major problems during
trenchless construction projects. The problems may arise from the fact that ground conditions
can have different impacts for various trenchless technology (TT) methods like HDD (Najafi,
2013).
In unstable soil conditions, it is difficult to maintain this stability for a long period. The risk
of collapse sharply increased with larger diameters of pipeline installation. For the pipeline
diameter above 36”, maintaining stability of the borehole has become an art, sophisticated
operators are required. Additionally, coarse soils allow liquids to flow through the individual
particles. For fine soils including clays and shales will usually prevent water from flowing
through the formation. Fine soils are reactive to water, and this must be considered when the
contractors want to select drilling fluids. Table 2 shows the classification of soils and their
impact on HDD process;
Below is identified risks, which are related to soil;Cohesiveness
 Collapsing Borehole
 Existing and Unidentified Subsurface Cavities and Obstacle
 Heave/ Hump on Surface
 Heterogeneous Soil
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High Abrasiveness
Change in Moisture Content
High Permeability of Soil
High Plasticity of Soil
Improper Liquid Limit
Improper Plastic Limit
High Swelling Limit
Land Sliding
Large Size of Soil Particle
Mixed Soil Condition
Multi-Layer Subsurface
Soil Hardness
Surface Subsidence
Unidentified Soil Content
Unpredictable Soil Behavior
Table 2. Type of Soil and their impact on HDD (Adapted from Najafi, 2010)
Type of Soil
Impacts
Fine ground: silt to clay
Joining with occasional clogging
Sandy or gravely grounds with fine sand: sandAbrasiveness, deviation and
gravel with clay
Eventually collapsing followed by
clogging
Grounds comprising of fines and the main elements: Abrasiveness, deviation and
clay or chalk with flint, fill or moraines
eventually sinking followed by clogging
Ground that is not sensitive to water: sand and pure
Partial to total mud loss
gravel
Instability of pulverulent materials
Rocks: carbonated, clay, silica, saline, magmatic and Rapid wear and tear of tools and the rig.
metamorphic
Impossibility of digging the tunnel across
grounds/rocks.
Organic ground, industrial wastes
Mud leakages, contamination by organic
matter
Equipment and Pipe: As stated earlier, the product pipe is pulled during installation by
HDD method. Therefore, there is a limitation in choosing pipe material. For pipeline
construction by HDD method, steel, High Density Polyethylene (HDPE), Medium Density
Polyethylene (MDPE), Polyvinylchloride (PVC), and ductile iron can be use (Najafi, 2013). All
this pipe material can be fused, welded, or joined mechanically to facilitate pulling. Selecting
appropriate drill rig size is important to minimize excess strain on the product pipe resulting
from a higher capacity of the machine. Therefore, understanding pull loads is important key
factor in drill rig selection (Ariaratnam, 2009).
Below is identified risks, related to equipment and pipe product;
 Control Device Failure
 Crane Operation Failure
 Defective Welding / Fusion
 High Surface Roughness of Pipe
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Improper Mixer Speed and Capacity
Improper Pull Head
Improper Spindle Speed
Improper Type of Drill Bit
Improper Type of Reamer
Inadequate Vacuum / Suction Capacity
Inadequate Rig Engine Horse Power (HP)
Inadequate Thrust/ Pullback
Inadequate Torque
Locator Failure
Low Tensile Strength Capacity of Pipe
Pipe Handlers Operation Failure
Pump Operation Failure
Rods failures
Separator Failure
Figure 3. Drilling Fluid Hydrofracture (Source: Google Image)
Operation and Management: One of the most common failure during pipeline installation
with HDD method is Hydrofracture or frac-out of drilling fluids as illustrated in Figure 3. Fracouts occur when the internal pressure in the borehole exceeds the external confining pressures
from the surround, which resulting in the drilling fluid escaping and drifting to the surface. This
could also occur if drilling in soils with fissures that provide a pathway to the surface
(Ariaratnam, 2009). Therefore, it is important to monitor the returns into the entrance pit to make
sure the amount of pumped fluid match with the amount of returns. Also, it can be avoided by
using proper tooling, drilling practices, and by monitoring drilling and pullback rates
(Ariaratnam, 2009).
The other biggest issue during pipeline installation by HDD is damage to existing
underground infrastructures, which can result in operation delay and extra cost of contractor.
Below is identified risk during operation and installation of pipeline by HDD method;
 Accident
 Damage to Adjacent
 Damage to Existing Underground Infrastructure
 Electrical Strike
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Equipment Operation Failure
Excessive Bending of The Rods
Excessive Torsional Moment to Tight or Loose Rods
Failure at Connecting the Product Pipe
Improper Drill Rig Positioning
Improper Jobsite Access
Improper Locating and Marking
Improper Maintenance of Equipment
Improper Pipe Handling
Improper Site Layout and Space Management
Improper Testing Procedure
Improper Tracking and Steering
Improper Traffic Management
Lack of Accuracy
Lack of Management Experience
Lack of Operator Skill
Lack of QA/QC
Miscommunication
Natural Gas Line Strike
Public Complains
Regulations and Legal Problem
Safety Issues
Security Issues
Supplier Issues
Unaware Environmental Regulation
Unidentified Underground Obstacle
Unreliable Subcontractor
Unskilled Labor
Welding / Fusion Equipment Operation Failure
CONCLUSION
Horizontal directional drilling, one of the most common trenchless installation methods, is a
steerable system used for the installation of pressure pipelines, cables and conduits. Most
underground and pipeline construction projects entail some risks due to unknown subsurface
conditions. Risk management is an important part of the decision-making process in
construction, and now widely accepted as a vital tool in the management of projects. The
ultimate purpose of developing these risk management techniques is to add value to project
delivery and improve efficiency of the construction industry during practice. Risk identification,
as an initial step of risk management, is to understand what is at risk within the context of the
project’s objectives and to generate a comprehensive inventory of risks based on the threats and
events that might prevent, degrade, delay or enhance the achievement of the objectives. For this
study, different risk identification methods used to identify and investigate four risk categories of
drilling fluid, soil, equipment and pipe, and operation and management to help project managers
(PMs) to have comprehensive checklists for their response strategy plan. PMs can use this
© ASCE
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checklist to develop and improve their QA/QC program to avoid any failure during pipeline
construction by HDD method. In addition, these risks can be analyzed and evaluated to develop
risk response plan.
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REFERENCES
Abdelgawad, M., Robinson Fayek, A., and Martinez, F. (2010). Quantitative Assessment of
Horizontal Directional Drilling Project Risk Using. Construction Research Congress.
Ariaratnam, S. (2009). Quality Assurance/Quality Control Measures in Horizontal Directional
Drilling. ICPTT-ASCE (pp. 1024-1035). ASCE.
Ariaratnam, S., and Beljan, I. (2005). Postconstruction Evaluation of Horizontal Directional
Drilling Installations. Practice Periodical on Structural Design and Construction , 115-126.
Gierczak, M. (2014). The quantitative risk assessment of MINI, MIDI and MAXI Horizontal.
Kangari, R. (1995). Risk Management Perceptions and Trends of U.S. Construction. Journal of
Construction Engineering and Management , 422-430.
Kohankar, Z., Tabesh, A., and Najafi, M. (2017). Risk Identification for Pipeline Installation by
Horizontal Directional Drilling. Proc. International Congress on Underground
Infrastructure, Water Management and Trenchless Technology (ICUWT), page 85-92,
Istanbul, Turkey
Lu, J., Su, w., and Liu, J. (2013). A Method for Horizontal Directional Drilling in Difficult Soil
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Miller , M., and Sayem, S. (2016). HDD Construction Observation and Documentation: Risk
Management and the Role of the Engineer. Proc. Pipelines . Kansas City, Missouri: ASCE.
Najafi, M., and Gokhale, S. (2005). Trenchless Technology: Pipeline and Utility Design,
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Najafi, M. (2010). Trenchless Technology Piping Installation and Inspection. McGraw-Hill.
Najafi, M. (2013). Trenchless Technology: Planning, Equipment, and Methods. McGraw-Hill.
Malek Mohammadi, M., Najafi, M., Tabesh, A., Riley, J. and Gruber, J. (2019) – Condition
Prediction of Sanitary Sewer Pipes, Accepted Paper, ASCE Pipeline Conference, 2019,
Nashville, TN, U.S.
Platosh, J. (2010). Trenchless Technology Helps Force Main Cross Harbor, Water World,
Visited on Feb 20, 2019. https://www.waterworld.com/articles/print/volume-26/issue6/editorial-features/trenchless-technology.html
Tabesh, A., Najafi, M., Ashoori, T., Tavakoli, R., And Shahandashti, S. (2017). Environmental
Impacts of Pipeline Construction for Underground Freight Transportation . ASCE Pipeline
(pp. 181-191). Phoenix, Arizona : ASCE .
Wood, G., and Ellis, R. (2003). Risk management practices of leading UK cost consultants.
Engineering, Construction and Architectural Management, Vol. 10 Issue: 4, 254-262.
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