Micropile Rock Anchors

[Fellin]

We are installing micropiles for a cell tower mat foundation to provide uplift resistance, so the micorpiles are essentially acting like rock anchors. My question; the profile is about 3 feet of weathered rock over competent granitic bedrock. Is there any reason in this case to have an unbonded length?, and what purpose would it serve if so? I was going to specify a minimum 15-foot micropile to provide about 10 feet in competent rock. Since we won't 'lock' off all the micropiles, I did't see a need for unbonded length, please advise.

 

[PEinc]

Micropiles do not have unbounded lengths. Unless these drilled members also support compression loads, you need tiedown anchors, not micropiles.

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