Section 3.
SOIL IDENTIFICATION
1. REQUIREMENTS. A complete engineering soil identification includes:
(a)
a classification of constituents, (b) the description of appearance and
structural characteristics, and (c) the determination of compactness or
consistency in situ.
a. Field Identification. Identify constituent materials visually
according to their grain size, and/or type of plasticity characteristics per
ASTM Standard D2488, Description of Soils (Visual-Manual Procedure).
(1) Coarse-Grained Soils. Coarse-grained soils are those soils
where more than half of particles finer than 3-inch size can be
distinguished by the naked eye. The smallest particle that is large enough
to be visible corresponds approximately to the size of the opening of No.
200 sieve used for laboratory identification. Complete identification
includes grain size, color, and/or estimate of compactness.
(a) Color. Use color that best describes the sample. If there
are two colors describe both colors. If there are more than two distinct
colors, use multi-colored notation.
(b) Grain Size. Identify components and fractions in accordance
with Table 2 - Coarse-Grained Soils.
(c) Grading. Identify both well graded or poorly graded sizes
as explained in Table 3, under Supplementary Criteria for Visual
Identification.
(d) Assigned Group Symbol. Use Table 3 for estimate of group
symbols based on the Unified Classification System.
(e) Compactness. Estimate compactness in situ by measuring
resistance to penetration of a selected penetrometer or sampling device (see
Chapter 2). If the standard penetration test is performed, determine the
number of blows of a 140 pound hammer falling 30 inches required to drive a
2-inch OD, 1-3/8 inch ID split barrel sampler 1 foot. The number of blows
thus obtained is known as the standard penetration resistance, N. The split
barrel is usually driven 18 inches. The penetration resistance is based on
the last 12 inches.
1) Description Terms. See Figure 1 (Reference 1, Soils and
Geology, Procedures for Foundation Design of Buildings and Other Structures
(Except Hydraulic Structures), by the Departments of the Army and Air
Force) for descriptive terms of compactness of sand. Figure 1 is applicable
for normally consolidated sand.
2) Compactness Based on Static Cone Penetration Resistance,
and Lunne, provides guidance for estimating relative density with respect
exploration, a q+c,-N correlation could be made, and Figure 1 is used to
describe compactness. If N is not measured, but q+c, is measured, then use
7.1-7
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