Description and Identification of Soils (Visual-Manual Procedure) - Soil Properties: Testing, Measurement, and Evaluation - page 29

Procedure for Identifying Fine-Grained Soils

(1) Select a representative sample of the material for examination.
Remove particles larger than the No. 40 sieve (medium sand and
larger) until a specimen equivalent to about a handful of material
is available. Use this specimen for performing the dry strength,
dilatancy, and toughness tests.

(2) Dry Strength:
(2.1) From the specimen, select enough material to mold into a ball
about 1 in. (25 mm) in diameter. Mold the material until it has the
consistency of putty, adding water if necessary.
(2.2) From the molded material, make at least three test specimens.
A test specimen shall be a ball of material about 1 ⁄ 2 in. (12 mm) in
diameter. Allow the test specimens to dry in air or sun or by artifi-
cial means, as long as the temperature does not exceed 60°C.
(2.3) If the test specimen contains natural dry lumps, those that
are about 1 ⁄ 2 in. (12 mm) in diameter may be used in place of the
molded balls.

Note 6 —The process of molding and drying usually produces
higher strengths than are found in natural dry lumps of soil.

(2.4) Test the strength of the dry balls or lumps by crushing be-
tween the fingers. Note the strength as none, low, medium, high, or
very high in accordance with the criteria in Table 3-8. If natural
dry lumps are used, do not use the results of any of the lumps that
are found to contain particles of coarse sand.

(2.5) The presence of high-strength, water-soluble cementing mate-
rials, such as calcium carbonate, may cause exceptionally high dry
strengths. The presence of calcium carbonate can usually be detected
from the intensity of the reaction with dilute hydrochloric acid.

(3) Dilatancy:
(3.1) From the specimen, select enough material to mold into a ball
about 1 ⁄ 2 in. (12 mm) in diameter. Mold the material, adding water
if necessary, until it has a soft, but not sticky, consistency.

Table 3-8 Criteria for Describing Dry Strength [1]

Description Criteria

None The dry specimen crumbles into powder with mere

pressure of handling

Low The dry specimen crumbles into powder with some

finger pressure

Medium The dry specimen breaks into pieces or crumbles with

considerable finger pressure

High The dry specimen cannot be broken with finger

pressure. Specimen will break into pieces between
thumb and a hard surface

Very high The dry specimen cannot be broken between the thumb

and a hard surface