horizontal directional drilling • chapter 12 horizontal directional drilling, the plastics pipe...
TRANSCRIPT
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
3
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
5
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
10
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
14
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
15
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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