Description and Identification of Soils (Visual-Manual Procedure) - Soil Properties: Testing, Measurement, and Evaluation - page 31

Table 3-11 Criteria for Describing Plasticity [1]

Description Criteria

An 1 ⁄ 8- in. (3-mm) thread cannot be rolled at any
water content

Nonplastic

Low The thread can barely be rolled and the lump can not

be formed when drier than the plastic limit

Medium The thread is easy to roll and not much time is required

to reach the plastic limit. The thread cannot be rerolled
after reaching the plastic limit. The lump crumbles when
drier than the plastic limit

High It takes considerable time rolling and kneading to reach

the plastic limit. The thread can be rerolled several times
after reaching the plastic limit. The lump can be formed
without crumbling when drier than the plastic limit

(6) Decide whether the soil is an inorganic or an organic fine-
grained soil. If inorganic, follow the steps given next.

(7) Identification of Inorganic Fine-Grained Soils:

(7.1) Identify the soil as a lean clay, CL, if the soil has medium to
high dry strength, none or slow dilatancy, and medium toughness
and plasticity (see Table 3-12).

Table 3-12 Identification of Inorganic Fine-Grained Soils from Manual Tests [1]

Soil Symbol Dry Strength Dilatancy Toughness

ML None to low Slow to rapid Low or thread cannot

be formed

CL Medium to high None to slow Medium

MH Low to medium None to slow Low to medium

CH High to very high None High

(7.2) Identify the soil as a fat clay, CH, if the soil has high to very
high dry strength, no dilatancy, and high toughness and plasticity
(see Table 3-12).

(7.3) Identify the soil as a silt, ML, if the soil has no to low dry
strength, slow to rapid dilatancy, and low toughness and plasticity,
or is nonplastic (see Table 3-12).

(7.4) Identify the soil as an elastic silt, MH, if the soil has low to
medium dry strength, no to slow dilatancy, and low to medium
toughness and plasticity (see Table 3-12).

Note 7 —These properties are similar to those for a lean clay.
However, the silt will dry quickly on the hand and have a
smooth, silky feel when dry. Some soils that would classify as
MH in accordance with the criteria in Test Method D 2487
are visually difficult to distinguish from lean clays, CL. It
may be necessary to perform laboratory testing for proper
identification.