Soil strength parameters from classification and testing - Geotechnical Investigation and Design Tables - page 58

Table 5.9 Peak friction angle (adapted from correlations in BS 8002, 1994).

Description Corrected SPT - N Critical state angle of soil (

crit )

30 A B

φ = + +

(blows/300 mm)

Angularity/shape (A) Grading (B)

(N o ) 60 N' C

Rounded Sub - Angular Angular

V. Loose 3 10 0 30 32 34 Uniform

≤ ≤

32 34 36 Moderate

Loose 3-8 34 36 38 Well graded

Med dense 8-25 20 2 32 34 36 Uniform

34 36 38 Moderate

36 38 40 Well graded

Dense 25-42 40 6 36 38 40 Uniform

38 40 42 Moderate

40 42 44 Well graded

V. Dense 42 60 9 39 41 43 Uniform >

41 43 52 Moderate

43 45 47 Well graded

5.10 Strength parameters from DCP data
•

The Dynamic Cone Penetrometer (DCP) is 1/3 the energy of the SPT, but the shape
of the cone results in less friction than the Split Spoon of the SPT.

•

n ∼ 1/3 (N o ) 60 used in the Table below.

•

The top 0.5m to 1.0m of most clay profiles can have a lower DCP value for a
given strength than shown in the Table, and is indicative of the depth of desiccation

Table 5.10 Soil and rock parameters from DCP data.

Material Description DCP - n (Blows/100 mm) Strength

Clays V. Soft 0-1 C u 0-12 kPa

=

Soft 1-2 C u 12-25 kPa

=

Firm 2-3 C u 25-50 kPa =

Stiff 3-7 C u 50-100 kPa =

V. Stiff 7-12 C u

=

100-200 kPa

Hard 12 C u 200 kPa > >

Sands V. Loose 0-1 30 ◦ φ <

Loose 1-3

φ =

30-35 ◦

Med dense 3-8 35-40 ◦

φ =

Dense 8-15 40-45 ◦

φ =

V. Dense 15 45 ◦ > φ >

Gravels, Cobbles, Boulders* 10 35 ◦

> φ =

>

20

φ >

40 ◦

Rock 10 C = 25 kPa, 30 ◦

> φ >

>

20 C > 50 kPa,

φ >

30 ◦

* Lowest value applies, erratic and high values are common in this material.