Building fills with SW-SM Material
Building fills with SW-SM Material
(OP)
We are importing type SW-SM material for a building pad. The specification clearly states SW and SM material is satisfactory. Fills for the building pad are from 0' to greater than 20'. Maximum rock size for fill in the specification is 3".
The site plans indicate to use ML or CL material for the building pad, but the specification, like specifications for many other projects, says ML and CL is unsatisfactory. The civil engineer stated in writing that the imported material meets the written specifications, but has deferred to the Geotech for a final decision.
The Geotechnical engineer has rejected the material.
Why would this material have been rejected?
Could larger sizes of rock be placed within 8' of subrade?





RE: Building fills with SW-SM Material
RE: Building fills with SW-SM Material
When you mean "Rock", is that your term for any coarse-grained soil(soils "above the line" on the USCS chart)?
The rock we wish to use is blasted from the site. I think is should be okay to fill using a 12" size rock or more, 8' or greater below subgrade.
RE: Building fills with SW-SM Material
based on the description given on this thread, i picture the phrase being the generic spec for structural fill that uually says max 3" or 6" particle size (not necessarily intended for rock fill recommendations). and this is usually stated that way to avoid having plumbing contractors trying to install pipes in rocky as heck conditions.
the geotech might have a problem with the CL material...or maybe there's too many outsized pieces for their liking. i wouldn't dare to guess since i don't know anything about the loads, grades, site conditions, soil conditions, fill material, etc. why not ask them why the material is rejected?
RE: Building fills with SW-SM Material
100 % passes the 3/8".
11.3% passes the #200 sieve.
Onsite material is clay and is unusable due to moisture and freezing issues. Knowing the time of year for construction, we decided to not completely balance the site and import select fill for the project - SW-SM.
The comment was that the material is apparently "too sandy" for the the fills and slopes we are building. However, the slopes will be "mowable" upon completion.
The rock size is merely a desire to get rid of as much shot rock as possible with minimal crushing.
The phrase is the generic spec. The building is a two story hospital.
RE: Building fills with SW-SM Material
is there something else going on here besides slope stability? by mowable i assume you're talking about 3:1 max. what you've presented doesn't make sense to me. my spider sense is tingling that the buck is being passed.
i could see issues about the mixing of shot rock into the soil more than the matrix being unusable because it peaks in the sands (w/ 11% passing #200). But, if the testing company (without the prelim geot report work) is calling the shots, i would understand that they are not interested in giving design input and will report the facts.
speculation on my part, very much so.
RE: Building fills with SW-SM Material
The same geotech that wrote the report is the onsite inspector. Geotech Report states that Borrow fill shall have less than 50% silt/clay by weight. Another contradiction. He knows the material we proposed and just "doesn't like it." It is too sandy.
We had the material tested by another Geotech at our expense(minimal)for this project.
We have found another source of material that he will approve. We may be able to break even cost wise using this material.
Did I just learn that SW-SM material is no longer usable for fill material? This is contrary to previous experience.
RE: Building fills with SW-SM Material
RE: Building fills with SW-SM Material
if using a nuke gauge (a sand-cone would also work, but don't try to test sands with a drive tube Hahaha),
take density testing at different probe penetrations. With surface testing (no probe penetration which is generally only a good testing procedure for road base stone), you may be failing because there is no confinement during compaction. But, after 2", 4", 6" and 8" probe embedment you may see an increase in compaction to nearly passing the test. And if you gently remove 4" and give a very flat surface for the gauge to sit on and then do a 8" probe embedment test, you may find that you have passed after all.
The overburden provides confinement during compaction. For very sandy soils (especially for a regional material i know as "processed fill"), i consider the 8" lift of soil that is immediately placed as a confining blanket and the target soils for compaction to be the previous blanket.
It's easier for the tester if the soil just passes from surficial testing. Soils that have confinement issues sometimes get false failing compaction tests as you can imagine from what i've described above. if you get passing tests on the surface (with 6" or 8" probe embedment of course), then the soil is probably good enough that confinement is not an issue and you'll need to continue getting surface passes.
I think with 11% passing #200 that it won't play to be that much of an issue, but keep this in mind if it comes up.
RE: Building fills with SW-SM Material
RE: Building fills with SW-SM Material
Some rock specs. I have used in the past include:
1) recommending an adequate amount of fine-grained materials in the rock to minimize the presence of voids.
2) capping the rock material up to 5 feet (pavements) and 10 feet (buildings) below final subgrade using filter fabric and structural fill.
3) be conscientious of future utilities that are deep. it would be very hard to trench smaller utilities that extend through rocky fill.
RE: Building fills with SW-SM Material
All is well.........until we start using the stuff.
RE: Building fills with SW-SM Material
GrumpyG,
"Possible sinkholes in the area ....."
Are the sinkholes limited in maximum size or diameter such that the shot rock will "filter" migration of the fill into the sinkhole? Out of curiosity, what's the source of the sinkholes?
RE: Building fills with SW-SM Material
Technically, Ordovician-aged, carbonate, Rickenbach Formation(Ori).
RE: Building fills with SW-SM Material
RE: Building fills with SW-SM Material
Is seismicity a concern in your area? Is there a high water table? If so, potential liquifaction may explain the geotech's concern.
That being said, we have used fills such as that described with a great deal of success here in the PNW (Vancouver Island). Keep your moisture contents slightly above optimum during placement and, as said earlier, test the lift below.
RE: Building fills with SW-SM Material
RE: Building fills with SW-SM Material
I just thought it was odd that the Geotech wanted a material with more clay and would not approve the SW-SM material.
With the 18-20'fills, the shot rock was easily used.
Thanks for everyone's input.