Sliding criterion (geotechnical engineering)

The sliding-angle is based on the ease with which a block of rock material can move over a discontinuity and hence is comparable to the tilt-angle as determined with the tilt test, but on a larger scale.

The sliding criterion has been developed for stresses that would occur in slopes between 2 and 25 metres (6.6 and 82.0 ft), hence, in the order of maximum 0.6 megapascals (87 psi).

The sliding criterion is based on back analyses of slope instability and earlier work of ISRM[5] and Laubscher.

(The values for the parameters are listed in table 1 and explained below) The roughness large scale (Rl) is based on visual comparison of the trace (with a length of about 1 m) or surface (with an area of about 1 x 1 m2 of a discontinuity with the example graphs in figure 1.

The roughness small scale (Rs) is established visually and tactile (by feeling).

The trace (with a length of about 0.2 m) or surface (with an area of about 0.2 x 0.2 m2 of a discontinuity is compared with the example graphs in figure 2; this gives stepped, undulating, or planar.

Infill material in a discontinuity has often a marked influence on the shear characteristics.

Softening infill material will under the influence of water or displacements, attain in lower shear strength and will act as a lubricating agent.

A sub-division is made between less thick and thicker than the amplitude of the roughness of the discontinuity walls.

Very weak and not compacted infill in discontinuities flows out of the discontinuities under its own weight or as a consequence of a very small trigger force (such as water pressure, vibrations due to traffic or the excavation process, etc.).