Page 266 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

226 Engineering Rock Mass Classification

TABLE 17.3 Some Modes of Failure in Slopes in Rock Masses—Cont’d

Failure Description (2) Typical materials (3) Figure (4)
mode (1) Toppling behind the 17.14(b)
Slide scarp at the top of a slide All rock types susceptible to block 17.14(c)
head toppling 17.14(e)
toppling Toppling of beds beneath 17.14(f)
Slide a slide mass due to shear Typically developed in any rock type 17.15(a, b)
base across their tops susceptible to toppling, located
toppling beneath the base of landslide (e.g., 17.15(c)
Rotary sliding in a single where the seat of sliding occurs along 17.16(a, b)
Block plane a fault surface)
torsion 17.16(c, d)
Tensile failure and fall or Blocky rock where sliding on the
Sheet sliding of hanging sheets potential slip surface is prevented by
failure a rock bridge, asperity, or other
Failure of intact rock that restraint which forms a hinge
Rock restrains block motion
bridge through compressive, Steeply dipping pre-existing sheet
cracking tensile, or flexural joints in granites and sandstone; new
cracking sheet joints in weathered rocks,
Slide friable massive sandstone, and
base Rupture of the rock mass pyroclastic sediments on steep slopes
rupture beneath the slide caused
by slide-transmitted Weak rock forming rock bridges;
Buckling shear and moment hard or soft rocks with impersistent
and kink Compressive collapse of discontinuities (as in some layered
band columns or slabs parallel sedimentary rocks, volcanic flow
slumping with the rock slope face rocks, block-jointed granites, and
foliated or jointed metamorphic
Soil-type Shearing with backward rocks)
slumping rotation, as in clay soils
Weak rock beneath the toe of a slide
Rock Hard rock under
bursting breaking stress Thinly bedded, weak sedimentary
rocks inclined steeply and parallel to
the slope surface; shale-sandstone
and shale-chert sequences, coal
measures, and foliated metamorphic
rocks

Weathered or softened clay shales;
thick fault-gouge; altered zones; soft
tuffs; high pore pressure zones

Granite and marble quarries into high
stressed rock; hard sedimentary rock
at the base of deep, narrow canyons

Source: Goodman and Kieffer, 2000.