Movements - Geotechnical Investigation and Design Tables - page 294

•

Creep settlement (also called secondary compression) occurs as a change of
structure occurs.

Table 23.2 Types of movements.

Principal soil types Type of movements

Immediate Consolidation Creep Swell

Rock Yes No No Some

Gravels Yes No No No

Sands Yes No No No

Silts Yes Minor No Minor

Clays Yes Yes Yes Yes

Organic Yes Minor Yes Minor

•

Immediate and consolidation settlements are dependent on the applied load and
the foundation size.

•

Self weight settlement can also occur for fill constructed of the above materials.
The settlement will depend on the material type, level of compaction and height
of the fill.

23.3 Immediate to total settlements
•

The settlement estimates are usually based on the settlement parameters from the
oedometer test.

•

This is mainly for consolidation settlements, but may also be applied to elastic
settlements for overconsolidated soils.

•

For stiff elastic soils, a factor of safety of 2.5 is assumed.

•

Secondary settlement is neglected in this table. Saturated soil is assumed.

Table 23.3 Immediate, consolidation and total settlement ratio estimates (after Burland et al., 1978).

Type of soil Immediate settlement, Consolidation Total settlement Ratio

(undrained) settlement

u /

ρ ρ ρ = ρ + ρ ρ ρ

u c T u c T

Soft yielding 0.1 1.1 10-15%

ρ ρ ρ <

oed oed oed

Stiff elastic 0.6 0.4 33-67%

ρ ρ ρ

oed oed oed

• ρ u / ρ T

→ 70% for deep layers of overconsolidated clays.

• ρ u / ρ T

25% for decreasing thickness of layer and increasing non homogeneity
and anisotropy.

→

23.4 Consolidation settlements
•

One - dimensional settlements = ρ od = ρ oed from the odeometer test (refer

chapter 11).