Soil strength parameters from classification and testing - Geotechnical Investigation and Design Tables - page 63

•

This may vary depending on the depth of the effective overburden and type of
coarse grained material.

Table 5.16 Preliminary sand strength from cone penetration tests.

Relative density Dr (%) Cone resistance, q c (MPa) Typical φ ◦

V. Loose D r 15 2.5 30 ◦ < < <

Loose D r

=

15-35 2.5-5.0 30-35 ◦

Med dense D r 35-65 5.0-10.0 35-40 ◦

=

Dense D r 65-85 10.0-20.0 40-45 ◦

=

V. Dense D r

>

85

>

20.0

>

45 ◦

•

The cone may reach refusal in very dense/cemented sands, depending on the thrust
of the rigs.

•

Rigs with the CPT pushed though its centre of gravity are usually expected to
penetrate stronger layers than CPTs pushed from the back of the rigs.

•

Portable CPT variations have less push although added flexibility for some difficult
to access sites.

5.17 Soil type from dilatometer test
•

The soil type can be determined from the material index parameter (I D ).

Table 5.17 Soil description from dilatometer testing (Marchetti, 1980).

I D 0.6 0.6 - 1.8 1.8

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Material type Clayey soils Silty soils Sandy soils

5.18 Lateral soil pressure from dilatometer test
•

The DMT can be used to determine the lateral stress.

•

Lateral stress coefficient K o = effective lateral stress/effective overburden stress.

Table 5.18 Lateral soil pressure from dilatometer test (Kulhawy and Mayne, 1990).

Type of clay Empirical Lateral stress coefficient K o

parameter β

k

Formulae 2 5 10 15

Insensitive clays 1.5 (K D /1.5) 0 . 47 - 0.6 0.5 1.2 1.8 2.4

Sensitive clays 2.0 (K D /2.0) 0 . 47 - 0.6 0.4 0.9 1.5 N/A

Glacial till 3.0 (K D /3.0) 0 . 47 - 0.6 N/A 0.7 1.2 1.5

Fissured clays 0.9 (K D /0.9) 0 . 47 - 0.6 N/A 1.6 2.5 3.2

•

Lateral Stress index K D = (p o -u 0 )/ σ

vo .

•

K D 2 indicates a possible slip surface in slope stability investigations (Marchetti

et al, 1993).

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