Horizontal Loop Under Gravel Driveway

Discussion in 'Geothermal Loops' started by Coz, Nov 14, 2019.

  1. Coz

    Coz New Member

    Hi everyone,

    Been reading the forums for a while here now actually, and have one question I can't seem to get a good answer on.

    We are currently designing out a site plan with our architect, and one of both our goals (and that of the HOA) is to not clear out more than the minimum number for trees for construction and safety. Lot is in a pine forest.

    To this end, it was suggested that a horizontal loop could be placed under the gravel driveway, prior to finishing the driveway. Possibly 5 feet deep or so.

    From my research I have found several several sites stating that horizontal under a driveway is no good because it does not get enough moisture. While I could understand that in the case of an asphalt driveway, would this same rule apply for a gravel driveway?

    This will be in Montana so depth would be pretty deep. Guessing 5ft ish. Soil is Gravely Loam.

    My initial concern would be the soil compacting above the loop making the soil more conductive towards the surface, but assume adding depth might help there.

    Any thoughts? Would I be happier just biting the bullet and going vertical? Or do we think we can make a horizontal system work under or near the driveway?

    The other possibility will also be the clearing of trees to trench the power in. Not sure how the power company would feel about loops a few feet under their power though. Anyone have any experience with this?

    Again goal is basically less clearing of trees, so if need be we can go vertical, but wanted to explore what options we had for horizontal placement with existing tree clearing requirements.

  2. Deuce

    Deuce Member

    Is the loop just crossing under the driveway or is it following under the driveway?
  3. Coz

    Coz New Member

    This would be following the driveway all the way. Clearing the trees for the drive, digging the trench, laying the loop, compacting, then building the driveway on top, 5-6 feet above the loop.
  4. Deuce

    Deuce Member

    I don't like that idea because what if a heavy truck should get stuck, sink and crush your loop field?
  5. gsmith22

    gsmith22 Active Member Forum Leader

    I know in my locale, where impervious land coverage is a concern, they would treat a gravel driveway as impervious due to the compaction that develops from the constant back and forth with vehicles. In reality, that may be a simplistic approach but it is likely that the ground would be more compact and less previous than areas outside of the driveway. Probably not completely impervious (like concrete or asphalt) but certainly not crushed stone previous (like in a french drain). For the western US where rain is very seasonally distributed, this might be a problem for a horizontal loop that could have the soil "dry out" and the ability of heat movement to/from the loop to diminish with lack of water. There was a poster on here in the last few months that was considering catching water from roof and using pipes to keep the ground wet around their horizontal loop - they were in the western US too. Here is that thread: https://www.geoexchange.org/forum/threads/diy-on-olympic-peninsula.7967/#post-65965

    Piping buried 5ft or more below grade should have little to no influence from surface loads - google Boussinesq curve Fig 2.18 from Buried Pipe Design by Moser. I think your bigger problem is the drying out aspect
  6. Coz

    Coz New Member

    Really good feedback. After reading that thread and checking the soil survey that someone suggested, my area is "Excessively drained" (Glaciercreek gravelly ashy silt loam). So not even sure watering will do a lot of good even if I wanted to set something like that up. Not sure I can do any more planning on this until they dig the well in the spring and we get the soil logs and water levels.

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