Page 265 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

Chapter 17 Types of Failures of Rock and Soil Slopes 225

TABLE 17.3 Some Modes of Failure in Slopes in Rock Masses

Failure Description (2) Typical materials (3) Figure (4)
mode (1) Gullies formed by action
Erosion, of surface or ground- Silty residual soils and saprolite 17.13(a–e)
piping water (especially disintegrated granite), 17.13(f–h)
silty fault gouge, uncemented sand 17.14(a, d)
Raveling Gradual erosion, particle rocks, uncemented noncohesive
by particle or block by pyroclastic sediments
Block block
sliding on Poorly cemented conglomerates and
a single Sliding without rotation breccias; very high fractured hard
plane along a face; single or rocks; layered rock masses being
Wedge multiple blocks loosened by active weathering (e.g.,
sliding thinly bedded sandstone/shale)
Sliding without rotation
Rock on two nonparallel Hard or soft rocks with well-defined
slumping planes, parallel to their discontinuities and jointing (e.g.,
line of intersection; layered sedimentary rocks, volcanic
Toppling single or multiple blocks flow rocks, block-jointed granites,
foliated metamorphic rocks)
Slide toe Backward rotation of
toppling single or multiple Blocky rock with at least two
blocks, moving into continuous and nonparallel joint
edge/face contact to sets (e.g., cross-jointed sedimentary
form one or more rocks, regularly faulted rocks, block-
detached beams jointed granite, and especially
foliated or jointed metamorphic
Forward rotation about rocks)
an edge — single or
multiple blocks Hard rocks with regular, parallel
joints dipping toward but not day-
Toppling at the toe of a lighting into free space and one flat-
slide in response to active lying joint that does day-light into
loading from above free space; multiple block modes
typically developed in foliated
metamorphic rocks and steeply
dipping sedimentary rocks; single
block modes develop in block-
jointed granites, sandstones, and
volcanic flow rocks

Hard rocks with regular, parallel
joints dipping away from the free
space, with or without crossing joints;
foliated metamorphic rocks and
steeply dipping layered sedimentary
rocks; also in block-jointed granites

All rock types susceptible to block
toppling

Continued