View Full Version : How to excavate/fill/build upon this?

04-15-2009, 12:27 AM
I'm putting together a design/bid for a raised patio to replace this...


We already demo'd the existing structure (everything above grade, and all the slabs on the ground), and ran into a gotcha of sorts. The existing structure was built with CMU, the blocks are buried at least 4 courses below grade around the perimeter of the structure and in the entire area of the steps. Obviously, being 32" below grade, the blocks are holding onto quite a bit of water. All of the fill inside the structure was/is clay.

Here's a quick layout of what may go in it's place...


The red line is the foot print of what we took out.

My question is, if I avoid placing my wall footings above the existing perimeter, can I avoid excavating/filling the existing block? If not, what should I do? Excavate just the buried CMU or excavate the entire area to the depth of the cmu/virgin soil? In either case, what should I use as fill? Clean 1.5" minus rock wrapped in textile (as we may do in the case of new construction)? Rip rap?

The new raised patio will be 30" above grade and likely filled with 1.5" minus w/ fines (crusher run).

What do you think the chances are the patio fill, wrapped in textile, will be stable enough to span the areas of buried CMU?

04-15-2009, 12:33 AM
Also, if I have to overdig the area of the previous structure should I then overdig the entire area of the new structure? I'll pretty quickly eat up this guys budget if so.

Old patio was roughly 10x16, new will be roughly 13x21.

04-15-2009, 08:59 AM
That's a tricky situation. You might very well have to dig out the whole thing. Might be a good idea to have an engineer check it out, last thing you want is all of your new work to settle.

04-15-2009, 09:14 AM
I was kinda thinking the same thing. Unfortunately. Never had to bring an engineer before... any idea of the cost? Guess I'll be hitting the yellow pages.

Anyone encounter something like this before? What did you do? I'd hate to lose this job, customer is a great guy, but I'd hate even more if it were to fail.

04-15-2009, 10:07 AM
Where's all the usual have-all-the-answers guys? Any ideas?

04-15-2009, 12:11 PM
Are you digging it out by hand or with an mini x? Geo isnt gonna save you here, theres another trick with the geo that i have done, in situations where i had settling problems. But all depends what you have spec'd in here for prices.

04-15-2009, 12:13 PM

what would your plan of attack be?

04-15-2009, 12:13 PM
i think you got tooo many stairs there as well on your drawing :P

04-15-2009, 12:19 PM
there's probably one too many going up to the door, as 3 steps would put a step level with the door... but otherwise... 7" steps... thats how many i need...

04-15-2009, 12:20 PM
Take it all out, might as well ....its gonna take 30 more mins? And run your base up. Dont worry on an over dig on this though. If you left it in your run the risk of when packing, busting up some of the CMU and some you wont..... I would however look at having a landing by the door and then maybe a step or two down, i hate the look of just steps to the door, without a landing pad.

04-15-2009, 12:52 PM
not looking for design advise at this point. like i said i just did a quick layout to get an idea of how the customers desired patio size might fit over the original footprint.

not anywhere near putting finishing touches on it.

anyway, take what all out, the entire area? 30 mins? Let's see... roughly 30' x 13' x 3' is something like 40-50 yards of clay and would require 90 or so tons of fill. let's not underestimate things here.

if you mean just take out the block... then i'll probably get uneven settling, no?

04-15-2009, 02:06 PM
Meant just the blocks..............if you compact your fill right it should be fine.

So is all the clay gone or whats there now?

04-15-2009, 02:20 PM
right now it just looks like a back yard, with a door conspicuously high above grade. heh

the fill from the patio is removed but everything at or below grade was left or spread.

04-15-2009, 10:24 PM
no ideas? anyone? for real.

just looking for a "i would...". we're usually full of those around here ;)

04-15-2009, 10:52 PM
Your project photo gives a strong impression that the original concrete decking/slabs were subject to deck heave. Either caused by expansive clay soil ( cover when wet and expanded, never when the clay soil is dry) or by frost heave. the reason I say frost heave is the information about the depth of the footings. Where is the frost line? minus 24"? Wow? Brrr, cold.
Man I'm from California and it's not that cold here to require footings that deep for such a structure. I would follow the other guys advice on this one and do complete excavation, geofabric, and place 3/4" crushed gravel 6" base-gravel has a 95% compaction element of poit to point contact -very stable. You could do grade beam and peir construction -used for unstable soil conditions.
ON another note: Be very careful with the type of material you select for a new deck -many of the decking composites are very temperature sensitive and will expand, contract, creak, groan and make noise, much to the dissatisfaction of your customer. So, especially follow the manufacturers installation instructions to the letter -some have you checking temp every half hour. and adjusting cuts in deck board lengths every 5- 10 degree change in temp., then you wait till the next day to install at same temp you cut. No Kidding -not for unskilled types.

04-15-2009, 11:02 PM
We're in NY, 4' frost is not unheard of. The raised structure will be a raised patio using SRW black and concrete paver decking.