Key geological issues - Geotechnical Engineering of Dams - page 65

Table 2.8. Typical characteristics of large rapid natural rock landslides (Glastonbury 2002, Glastonbury & Fell 2002c).

Translational slide class Compound slide classes

Large rock Rough Planar Bi-planar Curved Toe buttress Irregular Rock

Characteristics glide translational translational Toe buckling compound compound compound compound collapse

General Sedimentary Anisotropic Sedimentary Sedimentary Variable - Folded Anisotropic Irregular - Brittle cap rock

geology (esp. rock mass (esp. anisotropic sedimentary rock mass disturbed rock over argilla-

carbonate) carbonate) terrains mass ceous strata

Slide Mass Very thick, Some dis- Intact Intact Often highly Structure Often highly Often partly Intact

characteristics (several aggregation fractured to slope fractured fractured

hundreds of
metres) gen-
erally intact

Rupture surface Pre-sheared, Stress relief Pre-sheared, Pre-sheared, Bi-planar, Curved, Upper surface Irregular Rotational

characteristics bedding joints bedding bedding pre-sheared pre-sheared pre-sheared geometry geometry in low

defined defined defined strength rock

Rupture surface Very low 40º Typ 20-30º Typ 30-40º L 20-30º L 30º L 10-25º av 5-50º Variable -

inclination (10-20º) rotational

Rupture surface b typ 10-30º typ within typ within L b L typ L typ typ within 5º Variable

inclination v b greater 5º of b 5º of b 2-3º less 5º less of b

than b than b than b

Rupture surface Minimal High Minimal Minimal Some Minimal Minimal High Likely some

asperity
influence
Lateral margins High Moderate Moderate Low influence Variable Unknown Unknown Unknown Moderate

influence influence influence

Water influence Unknown Some Common Some Some Some Limited Unknown Some

First time/ First-time Predominantly Both First-time Both Both Both Both First-time

reactivated first-time

Slope history Glacial Fluvial and Fluvial Fluvial Glacial Fluvial and Fluvial and Fluvial and Fluvial

(Dominant cause) debuttressing glacial erosion erosion glacial glacial glacial

Pre-collapse Very limited Limited Limited Limited Unknown Some Common Limited Common

signs