For the soil described in Example 2.2, (liquid limit, ωL=38, plasticity index, IP = 21, and 82% passing #200 sieve), use the AASHTO table and USDA soil triangle to make a classification. Additional information: 20% sand, 60% silt, and 20% clay.

Question

For the soil described in Example 2.2, (liquid limit, [latex]ω_{L}=38[/latex], plasticity index, [latex]I_{P} = 21[/latex], and 82% passing #200 sieve), use the AASHTO table and USDA soil triangle to make a classification. Additional information: 20% sand, 60% silt, and 20% clay.

Accepted Answer

Using Table 2.4, when [latex]ω_{L}=38[/latex], and [latex]I_{P} = 21[/latex], the AASHTO classification is A-6, clayey soil. According to the USDA triangle Figure 2.5, the soil is a silt loam.

Table 2.4 AASHTO soil classification system
General	Granular materials							Silty clay materials
classification	(35% or less passing No. 200)							(more than 35% passing No. 200)
Group	A-1		A-2					A-4	A-5	A-6	A-7[latex]^a[/latex]
classification	A-1-a	A-1-b	A-3	A-2–4	A-2–5	A-2–6	A-2–7				A-7–5
Sieve analysis											A-7–6
Percent passing
No. 10	50 max
No. 40	30 max	50 max	51 min
No. 200	15 max	25 max	10 max	35 max	35 max	35 max	35 max	36 min	36 min	36 min	36 min
Characteristics
of fraction
passing
No. 40:
Liquid limit				40 max	41 min	40 max	41 min	40 max	41 min	40 max	41 min
Plasticity index	6 max		NP	10 max	10 max	11 min	11 min	10 max	10 max	11 min	11 min
Usual types of
significant
constituent	Stone fragments		Fine
materials	Gravel and sand		sand		Silty or clayey gravel and sand			Silty soils		Clayey soils
General rating as subgrade		Excellent to good						Fair to poor
Source: From Manual on Subsurface Investigations, 1988, by the American Association of State Highway and Transportation Officials (AASHTO),Washington DC. Used by permission.AASHTO publications may be purchased from the association’s bookstore at 1-800-231-3475 or online at http://bookstore.transportation.org Note [latex]^a[/latex] Plasticity index of a A-7–5 subgroup is equal to or less than LL minus 30. Plasticity index of A-7–6 subgroup is greater than LL minus 30.

Question 2.3: For the soil described in Example 2.2, (liquid limit, ωL=38,...

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