patio blocks really needed at every brace in hardpan soil?

[zephans]

Has anyone had problems with their pool caused by not having patio blocks supporting each column?

I read somewhere (possibly from HRDennis?) that patio blocks are needed on corners if your base material is very sturdy like hardpan (clay+rock mixture).

We've got very solid undisturbed hardpan soil and I am getting really tired of digging just the towers down. We have a 12'x24'x54" Diamond Star (Wilbar) if that makes any difference. I'll do it if people confirm it is important or if nobody has enough experience with missing patio blocks to make an informed opinion.

I'm starting with just the 4 corner towers in case I get some good news .

[zephans]

HRDennis already answered this question. Copying from Excavation thread:
HRDennis> Blocks should only be needed at the backs of the side braces.

Again, this is for undisturbed hardpan soil (rock and clay). Your mileage may vary.

[matt4x4]

I know Dennis allready answered this, but here's WHY you NEED patio blocks along the straight sides of a pool, but not along th curved ends:

For any pools that are round and don't need patio blocks - here's why - the pressure pushing outwards at any given point at equal height on the perimeter is equal, the force on the wall is opposite and equal, and since the wall is rigid up/down, no top portion will push out more than the bottom portion unless the metal would actually stretch/deform.

For an oval pool, the physics are different, a wall will lean because the oval pool continually wants to turn into a round pool 24/7 due to continuous water pressure, since the bottom of the wall is held/fastened in place, it does not move outwards, however, the top of the wall is not really held in place, therefore, the straight sides that want to move out to shape a circle will do so at the top portion, causing a lean.
We counteract that force through attempting to move/transfer this pressure down into the soil, so the force out, has to take a 90 degree turn and go down, in order to accomplish this, the angle bracket at the bottom of the post takes the full pressure - it continually wants to flip outwards - pulling the post away from the pool at the top, in soil, the individual soil particles are actually pretty easy to separate (even hard packed) and a lot of force on a small surface area can actually separate the dry dirt and allow for this bracket to bend out/over. Wet dirt is even worse, since the bonds between the dirt particles are now lubricated with water, therefore less friction.
A patio block makes it nearly impossible for the bracket to cut through the particles because the cement bond is stronger than the pressure it is receiving, and, the block provides a larger EVEN area for the pressure exerted to push into the dirt below, causing less pressure per square inch - after years of use - even though you have patio stones, you WILL see that they HAVE actually moved from level to an angle sloping away from the pool and the uprights are also angled, bigger patio stones = less outward movement, even then, once you get to a complete slab under your pool, the movement still occurrs - only this time, the stresses will deform the metal posts and brackets since they can no longer deform the dirt below.

[hrsdennis]

Great explanation Matt. Here’s the short version. The dirt around the pool will get wet from splashing and as soon as it does the sides will push out at the top. Happens every time.

Hope everyone has a great 4th of July. Dennis