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Chapter 5
5.1 Refer to Figure 5.1.
Soil
Classification
5.2 Modified percentages of sand, silt, and clay are calculated as follows:
Soil A: Modified % sand =
62.2%100
18
100
51 =×
−
22 =×
21
100
−
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Soil D: Modified % sand =
18%100
0
100
18 =×
−
Modified % silt =
24%100
0
100
24 =×
−
Modified % clay =
58%100
0
100
58 =×
−
Soil E: Modified % sand =
25%100
12
100
22 =×
−
Modified % silt =
29.5%100
12
100
26 =×
−
12
100
−
Refer to Figure 5.1.
5.3 Soil A: From Table 5.1, the soil is A-2-4. The GI for A-2-4 is zero.
Soil
Classification
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5.4 Soil 1: From Table 5.1, the soil is A-4. Eq. (5.1):
(50 35)[0.2 0.005(38 40)] 0.01(50 15)(9 10) 2.5
3
GI
= − + − + − − = ≈
5.5 According to Table 5.2, Soils 1, 2, 3, 5, 8, and 10 are fine-grained soils, since
36
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Soil 1: LL = 38 < 50; PI = 38 – 29 = 9. From Figure 5.3, plots below A-line.
From Table 5.2, group symbol: ML
Soil 2: LL = 56 ≥ 50; PI = 56 – 23 = 33. From Figure 5.3, plots above A-line.
From Table 5.2, group symbol: CH
Soil 3: LL = 37 < 50; PI = 37 – 22 = 15. From Figure 5.3, plots above A-line.
From Table 5.2, group symbol: CL
Soil 5: LL = 43 < 50; PI = 43 – 28 = 15. From Figure 5.3, plots below A-line.
From Table 5.2, group symbol: ML
Soil 8: LL = 40 < 50; PI = 40 – 21 = 19. From Figure 5.3, plots above A-line.
From Table 5.2, group symbol: CL
Soil 10: LL = 70 ≥ 50; PI = 70 – 38 = 32. From Figure 5.3, plots below A-line.
From Table 5.2, group symbol: MH
5.6 a. 13% passing No. 200 sieve; 38% passing No. 40 sieve; 90% passing No. 10
5.7 Soil A: Fine fraction = % passing No. 200 sieve = 3%; coarse-grained
Coarse fraction = 100 − 3 = 97%
Soil B: Fine fraction = % passing No. 200 sieve = 10%; coarse-grained
38
elastic silt with sand
5.8 Soil A: Fine fraction = % passing No. 200 sieve = 48%
Coarse fraction = 100 – 48 = 52%
Gravel fraction = 100 – 92 = 8%
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Soil D: Fine fraction = % passing No. 200 sieve = 60%
Coarse fraction = 100 – 60 = 40%
5.9 Soil 1: Fine fraction = % passing No. 200 sieve = 30%
Coarse fraction = 100 – 30 = 70%
Gravel fraction = 100 – 70 = 30%
Soil 4: Coarse fraction = 100 – 82 = 18%
Gravel fraction = 100 – 100 = 0%
Soil 7: Coarse fraction = 100 – 78 = 22%
Gravel fraction = 100 – 88 = 12%
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Soil 10: Coarse fraction = 100 – 2 = 98%
Gravel fraction = 100 – 100 = 0%
5.10 Coarse fraction = 100 – 11 = 89%
Gravel fraction = 9%
CRITICAL THINKING PROBLEM
5.C.1 a. Stratum 2
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Stratum 3
Stratum 4
Stratum 5
b. Stratum 2
Stratum 3
Stratum 4
Stratum 5