Geology Reference
In-Depth Information
it must be distinctly and clearly stated in log forms, summary
tables, reports, and the like that the symbol and name are based on
visual-manual procedures.
(1) The following examples show how the information required can
be reported. The information that is included in descriptions should
be based on individual circumstances and need.
EXAMPLES OF
VISUAL SOIL
DESCRIPTIONS [1]
(1.1) Well-Graded Gravel with Sand (GW) —About 75% fine to
coarse, hard, subangular gravel; about 25% fine to coarse, hard,
subangular sand; trace of fines; maximum size, 75 mm, brown, dry;
no reaction with HCl.
(1.2) Silty Sand with Gravel (SM) —About 60% predominantly fine
sand; about 25% silty fines with low plasticity, low dry strength,
rapid dilatancy, and low toughness; about 15% fine, hard, sub-
rounded gravel, a few gravel-size particles fractured with hammer
blow; maximum size, 25 mm; no reaction with HCl (Note—Field
sample size smaller than recommended).
In-Place Conditions —Firm, stratified, and contains lenses of silt
1 to 2 in. (25 to 50 mm) thick, moist, brown to gray; in-place density
106 lb/ft 3 ; in-place moisture 9%.
(1.3) Organic Soil (OL/OH) —About 100% fines with low plasticity,
slow dilatancy, low dry strength, and low toughness; wet, dark
brown, organic odor; weak reaction with HCl.
(1.4) Silty Sand with Organic Fines (SM) —About 75% fine to
coarse, hard, subangular reddish sand; about 25% organic and silty
dark brown nonplastic fines with no dry strength and slow dilat-
ancy; wet; maximum size, coarse sand; weak reaction with HCl.
(1.5) Poorly Graded Gravel with Silt, Sand, Cobbles and Boulders
(GP-GM) —About 75% fine to coarse, hard, subrounded to suban-
gular gravel; about 15% fine, hard, subrounded to subangular sand;
about 10% silty nonplastic fines; moist, brown; no reaction with
HCl; original field sample had about 5% (by volume) hard, sub-
rounded cobbles and a trace of hard, subrounded boulders, with a
maximum dimension of 18 in. (450 mm).
(1) Jar Method —The relative percentage of coarse- and fine-grained
material may be estimated by thoroughly shaking a mixture of soil
and water in a test tube or jar and then allowing the mixture to settle.
The coarse particles will fall to the bottom and successively finer par-
ticles will be deposited with increasing time; the sand sizes will fall out
of suspension in 20 to 30 s. The relative proportions can be estimated
from the relative volume of each separate size. This method should be
correlated to particle-size laboratory determinations.
SUGGESTED
PROCEDURES FOR
ESTIMATING THE
PERCENTAGES OF
GRAVEL, SAND,
AND FINES IN A
SOIL SAMPLE [1]
(2) Visual Method —Mentally visualize the gravel size particles
placed in a sack (or other container) or sacks. Then do the same
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