[treedoc1]

30' width from home foundation to edge of proposed SRW, sloping down away from the home

Inside that width insert a gunite pool that is 16' wide, centered.

That leaves me with about 7' width of backfill area on the far side of the pool., backfilling from the wall to the pool edge.

The SRW at that point is 8' tall from the downhill grade to the final deck level of the pool...we are enclosing the pool with the wall, has engineered plans that show the normal grid every 3 rows, clear 3/4" behind the wall with a drain to daylight, compact the soil fill to the 95% etc, etc.

I would prefer to utilize all fill as clean 3/4" and use no soil in the backfill (still utilizing the geogrids). I don't want any possibility of shear, that short width has me a little spooked.

The pool could stand on its own without the wall holding the fill...in essence the fill is for the poured concrete deck around the pool, I will be installing.

Unilock manufacturer (Betco Block/Oldcastle) says my idea is good and will provide a stronger fill.

Worth it or not? Cost of the material is minimal...peace of mind is not.

Thanks

Jim

[Paul]

Because there is no "extra load" on the wall you really don't need all that extra washed gravel. Your grid lengths of just over 5 foot should hold, we don't have soil type of the backfill so upping the grid to 6 foot should work. If soil backfill is running sand then all bets are off!

[Bill Schwab]

Jim:

I can appreciate your concerns regarding the pool/wall. Several things for consideration here, as we just finished a 6' wide, 6' high, 7 tier 157' long, with a total rise of 42'. Behind the top wall is a vanishing edge swimming pool that dumps onto the second highest tier.... In order to take the load off the walls the pool contactor was told to pour a 28'x47' (the whole dimension of the pools bottom by 42' tall slab of gunite, soil nailed into the mountain. By doing so, the loads were completely removed from the back of the walls, and with that much weight, pool popping from hydrostatic pressures will be next to impossible. There is one significant difference here. The soils we used for back fill are class 4 expansible clays. The mositure retention factor is 42 on a 30° stacking angle. Ideally, I would have been delighted to see 20-25 and we had a 4000 pad foot vibrator that fell off the slope 7 times during construction. It was a moe foe to get 90% out of to say the least, not to mention the day when I caught my guys blending soil by sparying water directly over the lifts of dirt rather than blending on the lower section.

On the toe, we had 38' of strata-grid 550 under the gunite pool base. And, that toe course was on 14' flat level ground at the bottom of the canyon, we cut the grade to accomodate our needs.

In your scenario, if I am reading this right, your wall is going to be placed in the center of a slope, which can be tricky. We have a code written called 7' to daylight. That means, the face of the wall from the toe course on a level measure, must be 7' from where the soil daylights, and what is usually means is there will be 4.5" of wall under ground, with grid from the toe course, every third row.

If the pool bottom can be set on top of the bottom grid length, or better yet if it could be made deeper, and you put some french drains around the pool base, you will probably be fine. Our wall withstood an earthquake of 3.4 magnitude during construction, and it was hairy for a few seconds, but nothing moved.

I have a series of pictures of how we built a 3 tier wall on a 2-1 slope I need to resize and I can send them off for others to see.

Do you have Keygrid? If not get it from Keystone.

Take your soil numbers and recreate the scenario the engineers give you from the drawings and if all the numbers jive, you should be fine. Also, it does not hurt to ask how well versed your engineer is with the Keystone product. It offends some of them, which does not bther me a bit, I don't do P.C. anyway.

Good luck, that sounds like a fun project!

[treedoc1]

thanks for the info

the slope is such that I will be burying 3 courses prior to hitting daylight..

I will determine what to backfill with once I get the material excavated and see what was thrown there when the house was built. Hopefully not too much clay.

Jim