interpretation of nuclear densometer test
interpretation of nuclear densometer test
(OP)
We want to compact sand to at least 95 % proctor. We have done laboratory tests on the material and have obtain the optimum density and an optimum water content of 11 %.
We are now doing nuclear density tests on the sand and the reading indicated a compaction of 98 to 100 % but for water content of 4 %.
My question is this: when reading the nucleodensometer what value should you be paying attention to, is it the compaction value or the water content ?
We are now doing nuclear density tests on the sand and the reading indicated a compaction of 98 to 100 % but for water content of 4 %.
My question is this: when reading the nucleodensometer what value should you be paying attention to, is it the compaction value or the water content ?





RE: interpretation of nuclear densometer test
If you are reaching 98 to 100% and the specification says that 95% is required, then you have met the requirement - unless there is also (as sometimes is) a requirement of the compaction being carried out at optimum +/- 2% (or other numbers). Keep in mind, though, that with sand there will be a dry out period so that the moisture content you are determining by the "machine" (or subsequently in the lab) may not be indicative of the moisture content at the time of compaction (time in delay of test to placment and compaction). Also, I found that you really should calibrate the nuclear density moisture content with the laboratory one. Back in the late 70s when our machine read water in lbs/ft3, I found that the machine was reading 30% too high - in other words, the lab moisture was 5% and the machine was reading 7%. You can see that by the machine reading "high", the density determined would be low by 1 to 2% depending on the material.
Another thing to keep in mind, some specifications also have a requirement that the average of the compaction readings must be greater than the specified value by some statistical coefficient. For 1 failure in 20, you would add (stdev * 1.65 + [ 1.65 / (sqrt[N]) ] where N is the number of compaction tests you took for the layer and stdev is the standard deviation of the "set" of compaction tests for a particular layer. If N < 10, there are methods to determine the standard deviation based on the range of values - if you think you have to go that way.
RE: interpretation of nuclear densometer test
The best way to test something is to squeeze it, slowly, until it breaks!
RE: interpretation of nuclear densometer test
This means calibrating as BigH indicates, not taking some "standard" reading in the lab on a concrete block or a paraffin block.
This form of testing is prone to all sorts of errors and they generally are on the low side, causing more grief on the jobs than necessary.
Being faster and easier does not relate to being better.
RE: interpretation of nuclear densometer test
To better explain this, there are a number of characterisitcs which may provide a high % compaction over a wide range of moisture contents, this is often the case with single sized materials such as sands. In affect, all the grains of sand are touching, which means that you get the same density over a wide range of moistures, however, with increasing moisture the voids fill with water and you reduce the air void content. This would be exhibited by a flat curve from the compaction. As a check to see if this is happening, you can also schedule compaction tests using the 2.5kg and 4.5kg rammer [different names in different countries] you may well find both curves overlie each other. The grading of the material can also be used to aid the assessment, try also calculating the uniformity coefficient for the sand.
RE: interpretation of nuclear densometer test
RE: interpretation of nuclear densometer test
1.-Material being compacted in field is different to that tested to determine the Maximum dry density in lab, the material in field could contain oversize particles that not were included within the lab test for instance, proctor maximum density and moisture content should be corrected by oversize fraction according to ASTM D-4718 in order that readings provided by the nuke are right, or lab material could contain a higher fraction passinf No. 200 sieve.
2.-Compaction equipment used in field compaction is heavier than requiered, heavier equipments will provide higher compaction energies, it means that effective efort used is grater than requiered, consequently, for the sime soil as compaction energy increases you need less moisture to reach certain density, this not mean that nuke or lab test are wrong, simply means that you have to improve field quality control program, If material is the same tested in lab, mositure content in field should be within an adequate range, lets say as BIG H plus or minus 2 for sandy soils, in order that your soil is being compacted as requiered, remember that as far as you appart your moisture content from theorical saturation curves as grater is the mechanical behavior drop in case of a suddenly moisture increase, that's the main reason to established and control a moisture content range
3.- Nuclear gauges has two radiological sources, the one located in the tip of the rod is used to measure density by the radiological attenuation principle and the mositure is measured by thermalization of hydrogen electrones, is like you bomb the H2O molecules using electrons the impáct termalized the electrons of hydrogen and produce an energiy emmision taht is measured by the gauge sensor, nevertheless this bombing not reach China, it is limited and the moisture content reading given by the nuke just reach a couple of inches as much as three, if you ar in a hot wheather location and the loss of moiture due to wind and solar radiation is high this can be affecting the reading, this thermalization also has a problem wich id that some kind of materials may produce false readings in moisture content and consequently dry density, for instance soils trated with hydrated lime (see the excess of hydrogen) will induce an error in the test, nevertheless there are correction that can be done to make the reading reliable, moisture, density, trench etc.. and usually correlate the nuke to sand cone and mositure content detrmined oven or direct heat dried samples are quite recommended
using the nuke requieres certain expertise degree by technician, because most of them use the value provided by lab and the reading provided by the machine and forgot the basics
RE: interpretation of nuclear densometer test
RE: interpretation of nuclear densometer test
When in doubt however, take a bulk sample at a nuke gauge location and pound a one point (dry side of optimum) and see if the one-point for the soil at the density test location falls on the original (i.e., reference Proctor) curve. If it does, then you are good. If it doesn't then you are referencing the wrong Proctor.
I also echo the comment that if you are testing much after the fill placement, the soil may have dried below the compaction moisture content. Dry density remains unchanged, but the measured moisture content is no reflection on the placement moisture content.
Fraught with problems, these compaction test projects.
f-d
¡papá gordo ain't no madre flaca!
RE: interpretation of nuclear densometer test