Horizontal Directional Drilling

Contents

• Overview

• Drilling process

– Pilot drilling, Reaming & Pull back

• General guidelines

• Equipment

• Borehole integrity

• Microduct installation

• Appendix

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Overview

• Definition

– Trenchless construction technology to install underground utility with minimal disruption of ground surface

– Direction adjustment using location sensor

– Up to 2,000m & 60” diameter PE pipe installable

• Steps

– Pilot drilling

– Reaming

– Pull back

Horizontal directional drilling

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Pilot drilling

• Process

– Boring by drill bit rotation or rod pushing

– At entry pit, rods supplied for sequential string connection

– Boring mud is supplied through rod

Drilling from entry to exit pit

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• Sensing of bit location

– RF signal & detector: wireless detection(battery driven) • Around 25m depth range(DigiTrak)

– Magnetic: wired & precise method

• Direction control

– By bit angle or rotation

• Video clips

– http://youtu.be/XJ64MvfJfkw

Direction control Sensing & adjustment

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Drilling mud

• Montmorillonite(Sodium)

– Clay of volcanic ash: absorbent Aluminum phyllosilicate

– 5% mix with water: swell(x 15), lubricant & gel state

• Function

– Drill bit cooling & lubricant, borehole suspension, soil cutting removal etc.

– Thixotropic: gel – sol change

Bentonite

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Reaming

• Borehole diameter enlargement

– To get enough diameter for pipe accommodation

– 120~150% bigger than utility pipe diameter

– If necessary, more than one pass reaming is done

Boring bigger path

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Reamer

• Depending on application

– Diameter and shape varies

Various types

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Pull back

• Installation of pipe

– Swivel, thimble & fuse are required for proper pulling

– At entry, each drill rod is removed after pulling

– Control of tensile load & deformation is important

Pipe pulling & install

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Pull back

• Pulling

– More than one pipe can be pulled at a time

– Excess length needed for shrinkage due to axial tensile elongation & thermal stabilization

– At exit pit location, butt fusion is done (PE preferred)

Pipe preparation

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General guidelines

• By experienced contractor & qualified engineer

– Select shortest reasonable distance for one continuous construction is possible

– Try to make as straight a drill pass as possible

– Make elevation difference of entry & exit pit minimum

– Locate all buried structures & utilities within 10~25ft from drill path

– Observe and avoid over-ground structures like power line

– Secure enough working space for rig, rods, pump & others

– Obtain “as-built” drawings for future use & protection

HDD process

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Equipment Site set up

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① Drilling rig

② Power unit

③ Drill rod

④ Water pump

⑤ Slurry mixing tank

⑥ Cuttings separation equipment

⑦ Slurry pump

⑧ Bentonite storage

⑨ Power generator

⑩ Spares storage ⑬ Slurry containment

⑪⑫ Office ⑭ Cuttings settlement pit

Equipment HDD manufacturers

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• Vermeer

• Ditch Witch

• Prime drilling GmbH

• American Augers

• Grundodrill

Borehole integrity

• Suspension of borehole

– Depending on the ground type, boring technique & presence of slurry etc.

– Slurry(mud & cutting mixture) acts to keep the hole open

– Parameters: Earth pressure, live load, groundwater pressure, internal pressure

Collapse & deformation

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Microduct installation

• Applicable cable – DB, DB Hybrid or DBR: Rigid & round shaped

• Pulling & termination – Never exceed the allowable tensile load of Microduct cable

– Swivel & fuse necessary

– Special care & measure to block mud or water ingress into Microduct/tube

• Excess length & test – Secure 3~4% length against shrinkage after pull back laying

– Do ball pass test directly after laying

Consideration

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Appendix

• Chapter 12 Horizontal Directional Drilling, The Plastics Pipe Institute Handbook of Polyethylene Pipe 2nd edition, PPI

• Horizontal Directional Drilling, Brochure of MEC, 2012

• Video clips

– horizontal directional drilling (HDD) demo video

– Horizontal directional drilling (how it works)

– Prime Drilling - Horizontal directional Drilling explained

– Horizontal Directional Drilling (HDD): How the Drill Bit is Steered

• Further reading

– Guidelines for Use of Mini-Horizontal Directional Drilling for Placement of High Density Polyethylene Pipe, TR-46, PPI, 2009

Reference & useful links

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