Lesson 4/Learning Event 2
Learning Event 2
IDENTIFY METHODS AND APPARATUS FOR THE UNDISTURBED SAMPLE METHOD
Tests on undisturbed samples are used when the base design calls for compacted soil, such as highly
compressible clay which loses strength upon remolding, or when correlating field in-place tests to the
design moisture condition.
Field control consists of taking samples for moisture content and density determinations as construction
proceeds. Densities obtained are compared with minimum densities established for the particular job.
Water contents are compared, generally, with the optimum moisture content previously established to
see that compaction is taking place within the desired range or to permit its adjustment, if necessary.
The preferred undisturbed field sample for checking density is the undisturbed sample of known
dimensions.
Lesson 3 of this subcourse covers soil samples in detail. In this lesson we will survey the three methods
of undisturbed sampling regular chunk, irregular chunk, and drive sampler. While newer methods are
being developed, these methods are still used in the field.
REGULAR CHUNK METHOD
As a military engineer you may direct your personnel to obtain a regular chunk sample. He or she will
remove a regularly shaped sample from an excavation in the subgrade (or test pit). The chunk is sealed
with three coats of melted paraffin. Then it is wrapped in cheese cloth, sealed in paraffin again, and
shipped to the laboratory in a specially constructed container. However, it may also be tested on site for
expediency.
IRREGULAR CHUNK METHOD
The regularly shaped sample is preferable, but sometimes large stones in the soil will prevent you from
obtaining one. In this case you will obtain an irregular chunk. This sample must also be sealed in
paraffin and carefully shipped to the laboratory. To determine the volume you will use water
displacement. Logically, the chunk sample methods do not work on cohesionless soils.
DRIVE SAMPLER METHOD
The drive sampler method is not truly an undisturbed sample method. Some compression may occur
particularly if a California Bearing Ratio mold (with a thicker cylinder) has been used. When taking a
cylinder sample, first measure and weigh the cylinder, then drive the cylinder into the soil using a hand-
held hammer. The sample is immediately sealed in the tube with paraffin.
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