Lesson 4/Learning Event 3
Learning Event 3
IDENTIFY METHODS AND APPARATUS FOR THE DISTURBED
SAMPLE METHOD
If the soil is not in proper condition during construction to remove an undisturbed sample, the density
determination requires measuring the volume of the hole after the sample is removed. The procedure
consists of filling the hole with a measured quantity of a known-density material, such as sand, oil, or
water, and computing the volume of the hole which is equal to the volume of soil removed. The soil's
moisture content and density are then determined. This method is called the disturbed sample method.
The method you choose depends on the type of soil and the equipment available. On moist, cohesive,
fine-grained soils, undisturbed samples using the samplers may be sufficient. Coarse-grained soils or
cohesionless oils make it difficult, obtain an undisturbed sample. In these soils, density determination
by the displacement method may be required. Sand-displacement may be used on any type of base
course or subgrade material. Oil-displacement cannot be used on highly pervious soils, or crushed stone
or slag base courses. In addition, if the pavement to be used is asphaltic concrete, the residual oil and
spillage will tend to soften the asphalt. Water-displacement requires the use of a balloon to contain the
water and can be used on any type of soil.
SAND DISPLACEMENT
The sand-displacement method may be used in either fine- or coarse-grained materials. This method is
so named because a calibrated sand is used to determine the volume of the hole from which the sample
has been taken.
Requirements
The test consists of digging out a sample of the material to be tested, determining the volume of the
hole, and determining the dry weight of the sample. There are three requirements that must be met for
this test:
The volume of the sample must be 0.05 cubic foot or larger.
A double-cone cylinder must be used. This permits calibrating the sand each day the tests are
performed.
The sand must be clean, dry and free-flowing with a constant moisture content while performing
the test. Uniformly-graded and well-rounded sand passing a #20 sieve and retained on a #40
sieve is most suitable for this test. There should be practically no material finer than the #200
sieve in the sand.
The volume of the jar and connecting cone up through the valve, and the empty weight of the apparatus
must be known before the sand can be calibrated. One other calibration must be made to account for
surface irregularities between the surface of the cone base and the surface to be tested.
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