Soil properties and state of the soil - Geotechnical Investigation and Design Tables - page 89

Table 7.21 Equilibrium soil suctions in Australia (NAASRA, 1972: Australian Bureau of Meteorology).

Location Equilibrium soil suction (pF) Climatic environment Annual average rainfall (mm)

Darwin 2 to 3 Tropical 1666

Sydney 3 to 4 Wet Coastal 1220

Brisbane 3 to 4 Wet Coastal 1189

Townsville Tropical 1136

Perth 2 to 3 Temperate 869

Melbourne 2 to 3 Temperate 661

Canberra Temperate 631

Adelaide 2 to 3 Temperate 553

Hobart 2 to 3 Temperate 624

Alice Springs 4.0 Semi - Arid 274 >

Table 7.22 Soil suction based on climate (AS 2870, 1996).

Climate description Soil suction change ( u, pF) Equilibrium soil suction, pF

Alpine/wet coastal 1.5 3.6

Wet temperate 1.5 3.8

Temperate 1.2-1.5 4.1

Dry temperate 1.2-1.5 4.2

Semi arid 1.5-1.8 4.4

7.23 Effect of climate on active zones
•

The deeper active zones are expected in drier climates.

•

Thornwaithe Moisture Index (TMI) based on rainfall and evaporation
rates.

Table 7.23 Active zones based on climate (Walsh et al., 1998).

Climate description H s (metres) Thornwaithe moisture index (TMI)

Alpine/west coastal 1.5

>

40

Wet temperate 1.8 10 to 40

Temperate 2.3 5to10 −

Dry temperate 3.0 25 to 5

− −

Semi arid 4.0 25

< −

7.24 Effect of compaction on suction
•

The compaction affects the soil suction.

•

Soils compacted wet of optimum has less suction than those dry of

optimum.

•

Heavier compaction induces greater soil suction.