Deformation parameters - Geotechnical Investigation and Design Tables - page 130

11.12 Soil modulus in clays from SPT values
•

The modulus varies significantly between small strain and large strain applications.

Table 11.12 Drained E and undrained E u modulus values with SPT N-value (CIRIA, 1995).

Material E /N (MPa) E u /N (MPa)

Clay 0.6 to 0.7 1.0 to 1.2

0.9 for q/q ult

=

0.4 to 0.1 6.3 to 10.4 for small strain values (q/q ult

<

0.1)

Weak rocks 0.5 to 2.0 for N 60

- u /N = 1 is appropriate for footings.

- For rafts, where smaller movements occur E u /N = 2.

- For very small strain movements for friction piles E u /N = 3.

11.13 Drained modulus of clays based on strength and plasticity
•

The drained modulus of soft clays is related to its undrained strength C u and its
plasticity index.

Table 11.13 Drained modulus values (from Stroud et al., 1975).

Soil plasticity (%) E /C u

10-30 270

20-30 200

30-40 150

40-50 130

50-60 110

11.14 Undrained modulus of clays for varying over
consolidation ratios

•

The undrained modulus E u depends on the soil strength, its plasticity and

overconsolidation ratio (OCR).

Table 11.14 Variation of the undrained modulus with overconsolidation
ratio ( Jamiolkowski et al., 1979).

Overconsolidation ratio Soil plasticity E u /C u

<

2 PI

<

30% 600-1500

2-4 400-1400

4-6 300-1000

6-10 200-600

2 PI 30-50% 300-600

< =

2-4 200-500

4-10 100-400

2 PI 50% 100-300 < >

2-10 50-250