Material and testing variability - Geotechnical Investigation and Design Tables - page 113

10.4 Soil variability from laboratory testing
•

The density of soils can be accurately tested.

•

There is a high variability on the shear strength test results of clays and the Plasticity
Index.

Table 10.4 Variability from laboratory testing (Poon and Kulhawy, 1999).

Test Property Soil type Coefficient of variation (%)

Range Mean

Atterberg tests Plasticity index Fine grained 5-51 24

Triaxial compression Effective angle of friction Clay, silt 7-56 24

Direct shear Shear strength, C u Clay, silt 19-20 20

Triaxial compression Shear strength, C u Clay, silt 8-38 19

Direct shear Effective angle of friction Sand 13-14 14

Direct shear Effective angle of friction Clay 6-22 14

Direct shear Effective angle of friction Clay, silt 3-29 13

Atterberg tests Plastic limit Fine grained 7-18 10

Triaxial compression Effective angle of friction Sand, silt 2-22 8

Atterberg tests Liquid limit Fine grained 3-11 7

Unit weight Density Fine grained 1-2 1

Table 10.5 Guidelines for inherent soil variability (Poon and Kulhawy, 1999).

Test type Property Soil type Coefficient of variation (%)

Range Estimated mean

Lab strength UC Shear strength, C u Clay 20-55 40

CIUC 20-40 30

UU 10-30 20

Lab strength Effective angle of friction Clay and sand 5-15 10

Standard penetration test N-value 25-50 40

Pressuremeter test P L Clay 10-35 25

Sand 20-50 35

E PMT Sand 15-65 40

Dilatometer A

Clay 10-35 25

B
A

Sand 20-50 35

B
I D Sand 20-60 40

K D 20-60

E D 15-65

Pressuremeter P L Clay 10-35 25

Sand 20-50 35

E PMT Sand 15-65 40

Cone penetrometer test q c Clay 20-40 30

Sand 20-60 40

Vane shear test Shear strength, C u Clay 10-40 25

Lab index Natural moisture content Clay and silt 8-30 20

Liquid limit 6-30

Plastic limit 6-30