Geology Reference
In-Depth Information
soil. These data, when plotted, represent a curvilinear relationship
known as the compaction curve . The values of optimum water content
and standard maximum dry unit weight are determined from the
compaction curve.
The actual step-by-step procedure is as follows (ASTM D 698-00 [2]):
(1) Soils:
(1.1) Do not reuse soil that has been previously laboratory com-
pacted.
(1.2) When using this test method for soils containing hydrated
halloysite, or where past experience with a particular soil indicates
that results will be altered by air drying, use the moist preparation
method [see (2)].
(1.3) Prepare the soil specimens for testing in accordance with
(2) (preferred) or with (3).
(2) Moist Preparation Method (preferred )—Without previously dry-
ing the sample, pass it through a No. 4 (4.75-mm), 3 8 -in. (9.5-mm), or
3
4 -in. (19.0-mm) sieve, depending on the method (A, B, or C) being
used. Determine the water content of the processed soil.
(2.1) Prepare at least four (preferably five) specimens having water
contents such that they bracket the estimated optimum water con-
tent. A specimen having a water content close to optimum should
be prepared first by trial additions of water and mixing (see Note
1). Select water contents for the rest of the specimens to provide at
least two specimens wet and two specimens dry of optimum, and
water contents varying by about 2%. At least two water contents
are necessary on the wet and dry side of optimum to accurately de-
fine the dry unit weight compaction curve [see (5)]. Some soils with
very high optimum water content or a relatively flat compaction
curve may require larger water content increments to obtain a
well-defined maximum dry unit weight. Water content increments
should not exceed 4%.
Note 1 —With practice it is usually possible to visually judge a
point near optimum water content. Typically, soil at optimum
water content can be squeezed into a lump that sticks together
when hand pressure is released, but will break cleanly into
two sections when “bent.” At water contents dry of optimum,
soils tend to crumble; wet of optimum, soils tend to stick to-
gether in a sticky cohesive mass. Optimum water content is
typically slightly less than the plastic limit.
(2.2) Use approximately 5 lbm (2.3 kg) of the sieved soil for each spec-
imen to be compacted using Method A or B, or 13 lbm (5.9 kg) using
Method C. To obtain the specimen water contents selected in (2.1),
add or remove the required amounts of water as follows: to add
water, spray it into the soil during mixing; to remove water, allow the
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