Movements - Geotechnical Investigation and Design Tables - page 296

Table 23.5 Typical potential self weight settlements (Goodger and Leach, 1990).

Compaction Material Self weight settlement

Well compacted Well graded sand and gravel 0.5% H

Shale, chalk and rock fills 0.5% H

Clay 0.5% H

Mixed refuse 30% H

Well controlled domestic refuse placed in layers 10% H

Medium compacted Rockfill 1.0% H

Lightly compacted Clay and chalk 1.5% H

Clay placed in deep layers 1.0-2.0% H

Compacted by scrapers Opencast backfill 0.6-0.8% H

Nominally compacted Opencast backfill 1.2% H

Uncompacted Sand 3.5% H

Clay fill (pumped) 12.0% H

Poorly compacted Chalk 1.0% H

23.6 Limiting movements for structures
•

The maximum allowable movement depends on the type of structure.

Table 23.6 Typical Limiting settlements for structures.

Type of structure Maximum allowable Reference

vertical movement

Isolated foundations on clays 65 mm Skempton and

Isolated foundations on sands 40 mm Macdonald (1955)

Rafts clays 65 to 100 mm

Rafts on sands 40 to 65 mm

Buildings with brick walls Wahls, 1981

L/H 2.5 75 mm • ≥

L/H 1.5 100 mm • ≤

Buildings with brick walls, reinforced with 150 mm

reinforced concrete or reinforced brick
Framed structures 100 mm

Solid reinforced concrete foundations of 300 mm

smokestacks, silos, towers
Bridges 50 mm Bozozuk, 1978

At base of embankments on soft ground
• Rail 100 mm

•

Road 200 mm

•

Movements at the base of an embankment is not equivalent to movement at the
running surface, which can be 10% or less of that movement. High embankments
provide a greater differential between the movements at the top and base, although
high embankments now experience greater self weight settlement.

•

Irrespective of the magnitude of the movements, often the angular distortion
may dictate the acceptable movements. Cracks may become visible at values