RE: Pier Depth

[Dennis]

How deep would you have to drill holes to set fiberglass pilings for a post & pier foundation?

[Seeb]

Pilings dont work that way they have to drivin into the ground so their cone shape can spread the load in soft ground. Pier here means a concrete footing(foundation)that you put a post on

[DanielP]

As ridiculous as it sounds to me, Piers can be set on a pile of tamped cinders. EEEE Gads Man!

[Liz]

nononono! Crushed rock is okay, but they made us redo the ones on tamped cinder.

aloha, Liz

"The best things in life aren't things."

[Dennis]

Let me rephrase this question. If you are building a post & pier foundation, I would think you cannot just put the piers on top of the ground. That being said, how deep should these be sunk into the ground? Hope this makes sense! Thanks!

[EightFingers]

Dennis, Have you talked to Hawai'i county about the requirements?

From what I was told depth required depends on the existance of soil or type of rock being built upon. There is no frost in Puna so there's no problem with heave as there is on most of the mainland. If you're building on solid pahoehoe, you should have no problem with surface piers.
Building on soil, depth required as well as the base bearing surface of the pier will have a lot to do with number of piers and type of house being built.
A talk with an engineer or planner who knows about Hawaii's soil mechanics would be helpful.

<Edited because LOML saw a misspelled word.> [B)]

[DanielP]

Liz,

Ya, I know, but in an earthquake, both will liquify. My grumble.

[Wao nahele kane]

If you’re talking about drilling a hole to set a marina grade fiberglass piling pier to build a house… better stop right there and go back to the drawing board. Those are not made for vertical type bearing loads nor intended to provide shear under such bearing loads.
If you’re just setting up a power pole or something, set it at about 24” if in solid Lava and fill the gaps with mortar mix then drill a small hole in the side and fill it just above grade with concrete.

A footing on solid rock for a post and beam supported structure only requires that the footing be pinned to the rock so there's no comparable answer to your question with regard to depth.

In that light if your setting a fiberglass piling pier for a power pole on solid rock just drill some small holes in the rock about the inner perimeter of the inner diameter of the tubes. Pump some epoxy in the holes and set some rebar sticking up out of the holes about 8- 14" and then bent over at 90 a few inches. Set the tubes around the rebar, drill a hole in the side of the tubes and fill them with concrete about 16" deep. That should secure them and keep them upright fairly stout.

[Dennis]

Here is the link to the web site that I happened upon. Maybe this application would only work in soft sandy environments and not into rock.

www.pearsonpilings.com

[Wao nahele kane]

The particular pilings specified could stand the load, although they are as you cited probably only rated for driving in sediment soils and another issue with driving in solid lava would be fracturing. In all reality there’s really no true valid reason to drive a pile for a house on solid lava. The expenses alone would be cost prohibitive for such a venture not to mention the gamble engineering wise… imagine driving a steel pile into the lava only to see it disappear down the hole when it hits a lava tube 20’ down (lol he he he, bye-bye).

It sounds as if you intend to build a full blown out structure/house. If you’re considering fiberglass for it’s resistances to moisture, insects etc… there are other alternatives that are far less expensive, concrete columns being one of them. Concrete columns for light loads such as residential homes do not easily succumb to seismic activity like heavy loaded municipal type concrete columns. If your concerns regarding concrete are seismic related then have them toss a mesh binder in the mix such as chopped fiber glass. The fibers will greatly impede any possible load fracturing that might remotely occur during a seismic event when combined with the steel rebar. You can also spec wire mesh just inside the perimeter surface of the concrete column to alleviate such concerns. Personally, I would never be concerned about a common concrete column with standard structural mix and common bar alone for a house.

Before you pour a concrete column on solid lava you will have to drill holes in the lava and use epoxy to adhere the rebar in the holes, these will act as pins ensuring that no slipping will occur at the foot joint effectively joining the concrete to the lava rock permanently. There are some pretty nifty concrete form systems available today and one is much cheaper than the common paper based Sono tube for round column forms. I’ve no clue as to your terrain conditions but you might be able to use the green building based Fast-Tubes for concrete column forms. For more info on this product you can contact Richard Fearn from Fab-Form and look through their website at http://www.fab-form.com/products/fasttube/fasttube.html

If you're building in/on Lava you've already got one of the best soils with regard to being structural friendly, there's no need to make things difficult or pointless.
BTW just to point out an errant term widely used in Hawaii - post and pier is a very poorly coined term and in all reality is nothing but jibberish even when one is using a concrete footing with a post atop it. It's properly cited as footing block post and beam. It's pier and beam if using a pinned concrete column or pinned steel columns with no specified footing. Piers are strictly members that are verticle and serve as a footing in direct contact with soils and then directly support a horizontal member.
Hope that helps.

E ho'a'o no i pau kuhihewa.