Pier and Beam foundations

v32870

Quick background:
I am building a small cabin (6 m x 4 m) off grid in north west Donegal. I have done a lot of research and pier and pad foundations are the most common types used for this type of project.

I want to cast 9 no. 300 mm diameter concrete piles. Pouring them into 300 mm diameter cardboard former's and nesting a 16 mm threaded bar into them to fix my 150 x 100 mm timber beam perimeter.

My question is in relation to the depth of the piers. How deep is the frost line generally in north west Ireland and is there a general rule of thumb for this foundation system ?

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BryanF

Hi we can’t offer structural advice here. suggest planning, followed by Engineer are your starting points

Calahonda52

BryanF wrote: »

Hi we can’t offer structural advice here. suggest planning, followed by Engineer are your starting points

As above, but you need to clarify the language:
is it piers on pads or full scale bored piles,

if the latter then the depth will be a function of the soil conditions, IMO the design will point to something much deeper than the frost line.

Is it cost effective to bring a piling rig in for nine piles or is it just a post digger on back of tractor you have in mind?

Again if piles, then you will need more than 16mm threaded bar, from an upward lift/wind design perspective, especially up there:D

Good luck with the project, you might share the progress, bearing in mind the no advice rules here

v32870

To be honest, its only 21 m2 cabin, 4m high and falls too 2m... To summaries the site it was previously bog but was excavated in filled with rubble. My plan was to dig 9no. holes, place my cardboard fomer's (1.5m long) into the holes which will be roughly 1 mtr deep.

I am however getting a second opinion from a structural engineer.

Lumen

Calahonda52 wrote: »

Again if piles, then you will need more than 16mm threaded bar, from an upward lift/wind design perspective, especially up there:D

I ran some fag-packet-internet-argument calculations on the proof load of M16 bolts and the bending strength of spruce, and it turns out that the 100mm beam will snap at more or less the same order of magnitude force that the bolts will let go, assuming perfect transfer of force from one to another.

This force being substantially higher that the weight of the shack, I predict that it will go airborne (piers attached) well before it disintegrates.

I think this was portrayed quite accurately in the 1939 documentary The Wizard of Oz.

Calahonda52

Lumen wrote: »

I ran some fag-packet-internet-argument calculations on the proof load of M16 bolts and the bending strength of spruce, and it turns out that the 100mm beam will snap at more or less the same order of magnitude force that the bolts will let go, assuming perfect transfer of force from one to another.

This force being substantially higher that the weight of the shack, I predict that it will go airborne (piers attached) well before it disintegrates.

I think this was portrayed quite accurately in the 1939 documentary The Wizard of Oz.

You run any numbers on the threaded bar pulling out of the piers: there will be zero or near zero grip in the threads

v32870 wrote: »

To be honest, its only 21 m2 cabin, 4m high and falls too 2m... To summaries the site it was previously bog but was excavated in filled with rubble. My plan was to dig 9no. holes, place my cardboard fomer's (1.5m long) into the holes which will be roughly 1 mtr deep.

I am however getting a second opinion from a structural engineer.

Bog=water table=possible mud slides
Rubble = trouble

Habitable= planning=water = run off= sewage provision

BryanF

Lads will ye post your PI insurance details for the OP

Calahonda52

https://dms.licdn.com/playback/C4E00AQEymayzX2ILOw/3a1bb112041b407393dbeb4ba95e1c14/feedshare-mp4_500/1479932728445-v0ch3x?e=1518800400&v=alpha&t=9V6aw4aeuThUPCQDBYKrCi2BDpbv56B6EO0DJ_hgJEg