Soil strength parameters from classification and testing - Geotechnical Investigation and Design Tables - page 59

cracks. Recently placed fills may also have lower values for a given strength than
shown in the Table.

5.11 CBR value from DCP data
•

The DCP is often used for the determination of the in situ CBR.

•

Various correlations exist depending on the soil type. Site specific correlation
should be carried out where possible.

•

The correlation is not as strong for values ≥ 10 blows/100mm (10mm/blow), ie

CBR > 20%.

Table 5.11 Typical DCP - CBR relationship.

Blows/100 mm In situ CBR (%) mm/blow

1 2 100 mm

< < >

1-2 2-4 100-50 mm

2-3 4-6 50-30 mm

3-5 6-10 30-20 mm

5-7 10-15 20-15 mm

7-10 15-25 15-10 mm

10-15 25-35 10-7 mm

15-20 35-50 7-5 mm

20-25 50-60 5-4 mm

25 60 4mm > > <

5.12 Soil classification from cone penetration tests
•

This is an ideal tool for profiling to identify lensing and thin layers.

Table 5.12 Soil classification (adapted from Meigh, 1987 and Robertson et al., 1986).

Parameter Value Non cohesive soil type Cohesive soil type

Measured cone 1.2 MPa - Normally to lightly

overconsolidated

<

Resistance, q c 1.2 MPa Sands Overconsolidated

>

Friction ratio 1.5% Non cohesive - <

(FR) 3.0% - Cohesive >

Pore pressure 0.0 to 0.2 Dense sand (q T 5 MPa) Hard/stiff soil (O.C) (q T 10 MPa) > >

Parameter B q 0.0 to 0.4 Medium/loose sand Stiff clay/silt

(2 MPa q T 5 MPa) (1 MPa q T 2 MPa) < < < <

0.2 to 0.8 Firm clay/fine silt (q T

<

1 MPa)

0.8 to 1.0 Soft clay (q T 0.5 MPa)

<

0.8 Very Soft clay (q T 0.2 MPa)

> <

Measured pore

∼

0 Dense sand (q T

−

P o > 12 MPa)

Pressure Medium sand (q T P o 5 MPa) − >

(u d - kPa) Loose sand (q T

−

P o > 2 MPa)

50 to 200 kPa Silt/stiff clay (q T P o > 1 MPa) −

100 kPa Soft to firm clay (q T P o 1 MPa) > − <