Movements - Geotechnical Investigation and Design Tables - page 303

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The free surface movement is used to classify the site reactivity.

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This applies for residential buildings and lightly loaded foundations.

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Competent rock excludes extremely weathered rocks, mudstones, and clay shales.

23.22 Free surface movements for road pavements
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The free surface movement can be used to classify the road subgrade movement
potential.

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Calculations should include the depth of pavement based on the strength criteria
design. Should pavements be excessive, a non reactive subgrade layer (capping
layer) is required below the pavement to reduce the reactive movement to an
acceptable value.

Table 23.22 Free surface movements for road subgrades (Look, 1992).

Road performance Surface movement (y s , mm)

Flexible pavements Rigid pavements

Acceptable 10 5 ≤ ≤

Marginal 10 to 20 5 to 15

Unacceptable 20 15 ≥ ≥

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Higher movements would be acceptable at the base of the embankment eg 100mm
for a high embankment on soft ground. That movement does not necessarily trans-
late to the surface area. This should be checked based on the embankment height.

23.23 Allowable strains for roadways
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The allowable rutting is based on the number of cycles applied to the pavement
layers.

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The design is based on ensuring each layer has not exceeded its allowable strain.

Table 23.23 Typical allowable strains for pavement layers (Austroads, 2004).

Material Allowable strains

Asphalt 1000 microstrain

Base at 0 to 10,000 cycles 2500 microstrain

Sub Base at 0 to 10,000 cycles 2000 microstrain

Base at 10,000 to 20,000 cycles 3500 microstrain

Sub Base at 10,000 to 20,000 cycles 4000 microstrain

Base at 0 to 20,000 to 30,000 cycles 5000 microstrain

Sub Base at 0 to 20,000 to 30,000 cycles 7000 microstrain