think Drew’s info is good. I
tend to be more
conservative so 135pcf is what I would use. If you know any Soils
engineers you may talk with him/her about the additional forces from
compactive effort upon the soil. Are they going to use a D6 and a
water truck to achieve compaction or maybe a vibratory piece of
How does that translate to actual load on roof. For you own protection
to get a soils engineer involved, even if sub consultant to you.
I use typically use 100
pcf for compacted dry
soil. This gives a porosity of about 40% (100 pcf / 62.4 pcf x
gravity of 2.6). Assuming that the voids are completely saturated, the
final saturated soil weight would be 100 pcf + 0.4*62.4 pcf = 125 pcf.
For a case of the backfill not being completely backfilled or the soils
a different average specific gravity, the saturated weight would vary.
Any geotechnical book should have further information.
I'm not sure how you plan to allow the water to drain off the
one thing to design for the weight, its another to design for the long
performance of the water proofing membrane on top of the concrete. You
could put a layer of coarse rocks on the membrane that would allow
drainage off the top. Cover this layer with some some of geotextile to
keep them in place and then with some sort of coarse backfill to allow
water to pass down vertically to the concrete cover and then laterally
structure. I would cover the walls with the same membrane or something
Along the perimeter, you could put in a french drain and run the outlet
laterally to some sort of underground vault for the water to drain out
from the shelter.
Some of the above can be eliminated if you are in a dry climate.
Some of the above can be eliminated if you are in a dry
have been ask to do a design for an underground
shelter. For now I am doing some preliminary calculations. The
shelter is basically a large concrete box structure 26’x54’ and
about 10’ high. It will be constructed in an open excavation and
then backfilled. The depth will be such that there will be 10’ of
fill over the top of the structure. There will be an architect and I
believe a mechanical engineer involved for the HVAC system. I have
questions for all those of you out there.
Dewatering has been discussed. At this point
would suspect it will take place over the roof of the structure and
side walls probably at the base. I will pitch to top of the roof slab
aid in dewatering. This morning I thought that a saturated soil
may develop over the top of the structure. I am not sure how deep a
saturated condition would develop, but at this point there is not a
geotechnical engineer involved. I would like to find some
“general” values for various soils in a saturated condition as I
don’t have any myself in my library. Does anyone out there have
some general values for saturated soil weights that I might use for
preliminary designs? Also for lateral pressures?
Trying to save a little time for now. So
Joseph R. Grill,