User:Robth/sandbox2

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The HDD technique can be used in various ground conditions including hard rock, sand, silt, clay formations. The bore hole is supported by drilling fluid mainly consists of bentonite, which has several functions including transport of cuttings, cooling off drill bit, sealing and support the drilled hole, lubrication to reduce friction during pullback.

HDD offers several advantages when compared to other construction methods:

• Minimal social and environmental disturbance
• No interruption to surface traffic
• Complicated crossings can be quickly and economically accomplished with a great degree of accuracy
• Sufficient depth can be accomplished to avoid other underground utilities.
• In landfall crossing, there is no excavation of shoreline nor obstruction on seabed.
• In river crossing, the danger of river bed erosion and possible damage from river traffic is eliminated.
• Requires only a small construction footprint and hence minimal reinstatement works.

For Landfall HDD, the product pipe can be pulled into the reamed hole from:

• onshore (pulled from a HDD rig located on a drill barge)
• seabed (pulled from a HDD rig located onshore)
• laybarge (pulled from a HDD rig located onshore)

depending on prevailing space, ground, sea, equipment, etc. limitations.