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When my house was built, it had (very stupidly) dirt backfill piled up against exterior brick veneer, to an elevation 12″ higher than mudsill & subfloor. Needless to say, extensive damage to the framing occurred, which has now been repaired. So, now I have 2-3 foot deep, 10 foot long trench next to the brick veneer on the side of the house.
For various practical & architectural reasons, I want to pour concrete steps in this trench, running parallel to & immediately adjacent to house for about 10 ft. (there is a natural grade, about 3 ft elevation difference, I want to span with the steps).
>>> the question is, what’s the “best” or most appropriate fill/base to put under the steps?
In places, the fill would be nearly 3 foot deep. I clearly want the base to be free draining & not wick up any moisture, so no way am I going to use soil (remember, the fill would be higher in elevation than the mudsill & subfloor).
I hear about “compactable dense aggregate” stone, but will this drain well?? Does pea gravel make an acceptable fill/ base under concrete? It does drain well, but does it compact or otherwise remain locked in place? what are my options?
note, I live in So Calif, so there is no freezing problem. The local soil is sandy & “relatively” free draining. Rainfall is light but can be 25″ in a wet year.
Thanks in advance.
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Hi Tom,
I'm not a hundred percent on what your doing, so I will confine my answer to the pea stone issue.
In basic terms. picture a bag of marbles. The bag won't stay up because all the marbles are round, consistent in size and when pressure is exerted against the bag, the marbles displace instead of packing.
Compaction is easier, when sand or stone or a combination of both is irregular in shape, size and consistency. Crushed stone, 3/4 to 7/8, will compact like a concrete walkway but will still drain like a sieve.
Hope this helps,
Gabe
*3/4 stone will drain great.. and it is small enuf thta you can actually move it withh a shovel to grade it....but if it gets choked with fines (fine dirt silting in ) then you are right back where you started.. do two things... line the side of your trench with a filter fabric, let it flop on the banks .. place your stone and then cover it with more filter fabric..this will create a boundary between the dirt and the drainage stone... filter fabric is usually availabel to heavy and highway and drainage contractors.. a good substitute is the they sell at good lumber yards now so residential contractors can comply with some of teh regulations about protection of wetlands...the 2d thing is you have to provide an outlet for the water or you will just be creating an underground pool.. if the perc rate of your soil is good enough.. no problem.. if not lead a perf pipe thru the stone to daylight to let the water out of your trench..Kermit
*Real quick, simple and easy, provided you have a good stone supplier in your area.First line the trench with filter fabric as stated above. Next put in the black PVC drain tile and give it an outlet away from the foundation. Next fill the hole with number 6 stone, fresh or recycled concrete doesn't matter. Fill it to about 1 foot from the top of the hole and top off with "Crush and Run" or another similar type its "Bank Run." This is basically unwashed stone that compacts and drains very well.I assume you want to compact as you fill so the concrete doesn't settle. I have used this tech in areas here in Baltimore were surface water is a problem. On top of the crush and run sod was placed and you couldn't tell there was a ditch or drain system. and no sunken area ever developed.AEBTW #6 stone is about 3/4" and crush and run is slightly larger with all the broken chips and dust still mixed in. Fresh out of the crusher. Also Crush and run is stable in the weather after it is compacted if it is going to be a while before you can pour.