Soil properties and state of the soil - Geotechnical Investigation and Design Tables - page 78

Table 7.1 ( Continued )

Property Sands Clays Comments

softening may occur in the surface. See Table 21.4

cuttings and softened for N q bearing capacity

strength (cohesion loss) factor (becomes significant

then applies. at 30 ◦ ).

φ >

Compaction Influenced by vibration. Influenced by high Deeper lifts can be

Therefore a vibrating pressures. Therefore a compacted with sands,

roller is appropriate. sheepsfoot roller is while clays require small

appropriate. lifts. Sands tend to be

self compacting.

Settlement Occurs immediately (days Has a short and long A self weight settlement

or weeks) on application term (months or years) can also occur in both. In

of the load. settlement period. clays the settlement is

made up of consolidation
and creep.

Effect of climate Minor movement for Soil suction changes These volume

seasonal moisture are significant with changes can create

changes. volume changes heave, shrinkage uplift

accompanying. pressures. In the longer

term this may lead to
a loss in strength.

•

In cases of uncertainty of clay/sand governing property, the design must consider
both geotechnical models. The importance of simple laboratory classification tests
becomes evident.

•

Given the distinct behaviour of the two types of soils, then the importance of
the soil classification process is self-evident. The requirement for carrying out
laboratory classification tests on some samples to validate the field classification
is also evident. Yet there are many geotechnical reports that rely only on the field
classification due to cost constraints.

7.2 State of the soil
•

The state of the soil often governs the soil properties. Therefore any discussion of
soil property assumes a given state.

Table 7.2 Some influences of the state of the soil.

Soil property State of soil Relative influence

Strength Dry High compaction High OCR Higher strength

Wet Low compaction Low OCR Reduced strength

Colour Dry Lighter colour

Wet Dark colour

Suction Dry High compaction High OCR High suction

Wet Low compaction Low OCR Low suction

Density High compaction High OCR High density

Low compaction Low OCR Lower density