Movements - Geotechnical Investigation and Design Tables - page 301

23.16 Settlements adjacent to open cuts for various
support systems

•

These are empirically derived values for horizontal movements at the crest of an
excavation.

•

This may be conservative for residual soils, and with recent advances in construc-
tion procedures.

Table 23.16 Horizontal movements for varying support systems (Peck, 1969).

Type of wall Horizontal movement as %

of excavation height

Externally stabilised Cantilever retaining walls 0.5%

Propped retaining walls 0.2-0.5%

Tied back walls 0.05-0.15%

Internally stabilised Soil nails 0.1-0.3%

23.17 Tolerable displacement in seismic slope stability analysis
•

When seismic factors of safety < 1.15 then this initial screening should be replaced

by a displacement analysis.

Table 23.17 Tolerable displacement (after Duncan and Wright, 2005).

Slope type Tolerable displacement

Typical slopes and dams 1.0 m

Landfill covers 0.30 m

Landfill base 0.15 m

23.18 Rock displacement
•

A probability of failure of less than 0.5% could be accepted for unmonitored
permanent urban slopes with free access (Skipp, 1992).

Table 23.18 Permanent rock displacement for rock slope analysis (Skipp, 1992).

Failure category Annual probability Permanent displacement

Catastrophic 0.0001 3

Major 0.0005 1.5

Moderate 0.001 0.3

Minor 0.005 0.15