Existing Subgrade - no fill - Do you check for soil density as if it were fill.
Existing Subgrade - no fill - Do you check for soil density as if it were fill.
(OP)
After an area is excavated for footings, do you check for soil for density, or do you assume subgrade is suitable without testing. I have a project where Nuclear Gauage was used with failing tests, no fill was used.






RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
Dik
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
Given my situation in the semi-arid western Colorado, I am continually using the nuc gauge to confirm in-place conditions. I have been doing this for virtually all open-excavtion observations since about 1992. I wish I had started this when working for my Father back in the mid 1960's.
Given my local geology of Expansive Bedrock materials, potential collapsible soils from debris fan deposits, potential collapsible soils from alkali (sulfate) cementation, very 'movable' soils (dispersive-like characteristics) when subjected to the infiltrating groundwater and enormous soils density differences in former agriculture areas (the low-density plow layer vs. the compacter zone immediately beneath the plow layer).
I have a fairly specific set of criteria for a number of soil conditions. Most of these are to confirm the actual design conditions of the Geotechnical Reports are met. The actual criteria is NOT % compaction, but rather a minimum/maximum unit weight which corresponds with the conditions of the Geotechnical Reports. I have not figured out the logic of some of the local 'others' who are always trying to obtain a standard % compation..
Are your footings to be bearing on undisturbed soil?
The undisturbed soil needs to be properly defined. In some areas, This criteria leads to an enormous number of small problems which can plague local foundations.
Use of a Nuclear Gauge to determine the density of undisturbed native soil has no value, even if they took a sample and ran a 5 point Proctor test on it.
Come to my area. I have a number of attorneys to introduce you to. I also have a soil rock/profile which I would love to hear your superior opinion.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
The consensus is that density testing has no value. But I still have spongy spots, so I have asked that they be removed and replaced with RCA.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
that is definitely not the consensus. I think a more accurate consensus is that many contractors (and also owners and some engineers) don't want to spend money on additional QC testing or field inspection.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
Density is density. If you need it in the fill, you need in "undisturbed" soil as well. Undisturbed does not mean that the soil is competent. You have to check this with a variety of tests, including in-place density.
In my opinion it is a false assumption that undisturbed soil needs no further evaluation or treatment.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
So the question remains, is density testing (with passing results) for bottom of footings of non-disturbed soils required under ICC International Building Code (2015) requirements, or not.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
No. The 2015 version of the IBC does not specifically require density testing in subgrade soils that are not fill; however, it does require that you verify that proper bearing capacity in the subgrade will be achieved under shallow foundations. See Table 1705.6
Keep in mind that prescriptive methods of the code are MINIMUM requirements. The geotechnical engineer can require more; however, in your case, apparently he/she has not done so and does not see the importance of it. I would disagree and reiterate my previous point.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
Why do you disagree with the Geotech? From what I gather so far is that the soil (unknown classification) is less than 95% (of what: standard proctor, modified?) And, the Geotech has visited the excavations and stated that the code does not require density testing and it is suitable for the new foundations.
We don't know the loads on the new foundation, whether the <95% is standard or proctor, nor how far below 95% the density test show. Since the results are given in a percentage, should we assume the soil was tested in a lab to determine maximum?
Since I am not a geotechnical engineer and have incomplete information, I would assume that the geotech has given the proper standard of care for this project.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.
@OG....I agree with your assessment. I've done many myself; however, that process is an engineering evaluation based on experience and backed by some level of test evaluation done in the past whether you did plate load tests, penetrometers, density testing, probe rods or jumping up and down in the footing. All are evaluative.
With all due respect to PT999 I think he did the right thing. Perhaps with his level of experience he wanted a greater comfort level with the subgrade. Nothing wrong with that. If the geotech was able to come out to the site and make a further engineering assessment of the conditions to override PT999's need for further information, that's great. PT999 was not the geotech of record and that decision, absent relevant test data, was not his to make and he made the right call.
RE: Existing Subgrade - no fill - Do you check for soil density as if it were fill.