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Unit Weight of Soil
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Unit weight of a soil mass is the ratio of the total weight of soil to the total volume of soil.
Unit Weight, g, is usually determined in the laboratory by measuring the
weight and volume of a relatively undisturbed soil sample obtained from a brass ring.
Measuring unit weight of soil in the field may consist of a sand cone test, rubber balloon
or nuclear densiometer.
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Empirical values for g, of granular soils
based on the standard penetration number, (from Bowels, Foundation Analysis).
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SPT Penetration, N-Value
(blows/ foot)
|
g (lb/ft3) |
|
0 - 4
|
70 - 100
|
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4 - 10
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90 - 115
|
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10 - 30
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110 - 130
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30 - 50
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110 - 140
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>50
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130 - 150
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Empirical values for g, of cohesive soils
based on the standard penetration number, (from Bowels, Foundation Analysis).
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SPT Penetration, N-Value
(blows/ foot)
|
gsat
(lb/ft3) |
|
0 - 4
|
100 - 120
|
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4 - 8
|
110 - 130
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8 - 32
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120 - 140
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Typical Soil Characteristics (from Lindeburg, Civil Engineering Reference Manual for the PE
Exam, 8th ed.)
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Soil Type
|
g
(lb/ft3) |
gsat
(lb/ft3) |
|
Sand, loose and uniform
|
90
|
118
|
|
Sand, dense and uniform
|
109
|
130
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sand, loose and well graded
|
99
|
124
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Sand, dense and well graded
|
116
|
135
|
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glacial clay, soft
|
76
|
110
|
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glacial clay, stiff
|
106
|
125
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Typical Values of Soil Index Properties (from NAVFAC 7.01)
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Soil Type
|
g
(lb/ft3) |
gsub
(lb/ft3) |
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Sand; clean, uniform, fine or medium
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84 - 136
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52 - 73
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Silt; uniform, inorganic
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81 - 136
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51 - 73
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Silty Sand
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88 - 142
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54 - 79
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Sand; Well-graded
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86 - 148
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53 - 86
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Silty Sand and Gravel
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90 - 155
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56 - 92
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Sandy or Silty Clay
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100 - 147
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38 - 85
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Silty Clay with Gravel; uniform
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115 - 151
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53 - 89
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Well-graded Gravel, Sand, Silt and Clay
|
125 - 156
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62 - 94
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Clay
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94 - 133
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31 - 71
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Colloidal Clay
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71 - 128
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8 - 66
|
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Organic Silt
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87 - 131
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25 - 69
|
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Organic Clay
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81 - 125
|
18 - 62
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Typical Soil Characteristics (from Lindeburg, Civil Engineering Reference Manual for the PE
Exam, 8th ed.)
|
Soil Type
|
g
(lb/ft3) |
gsat
(lb/ft3) |
|
Sand, loose and uniform
|
90
|
118
|
|
Sand, dense and uniform
|
109
|
130
|
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sand, loose and well graded
|
99
|
124
|
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Sand, dense and well graded
|
116
|
135
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glacial clay, soft
|
76
|
110
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glacial clay, stiff
|
106
|
125
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Other soil and soil related properties are listed below:
Angle of Internal Friction
Bearing Capacity Factors
Cohesion
External Friction Angle
Factor of Safety
Lateral Earth Pressure Coefficients
Modulus of Vertical Subgrade Reaction
Soil Unit Weights
Young's Modulus or modulus of elasticity
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