Sliding criterion (geotechnical engineering)
Encyclopedia
Sliding criterion
The sliding criterion is a tool to estimate easily the shear strength
properties of a discontinuity
in a rock
mass based on visual and tactile (i.e. by feeling) characterization of the discontinuity
. The shear strength of a discontinuity is important in, for example, tunnel
, foundation, or slope
engineering, but also stability of natural slopes
is often governed by the shear strength along discontinuities.
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 m, hence, in the order of maximum 0.6 MPa. The sliding criterion is based on back analyses of slope instability and earlier work of ISRM and Laubscher. The sliding criterion is part of the Slope Stability Probability Classification
(SSPC) system for slope stability analyses.
(The values for the parameters are listed in table 1 and explained below)
with the example graphs in figure 1. This results in a descriptive term: wavy, slightly wavy, curved, slightly curved, or straight. The corresponding factor for Rl is listed in table 1.
The roughness large scale (Rl) contributes only to the friction along the discontinuity when the walls on both sides of the discontinuity are fitting, i.e. the asperities
on both discontinuity walls match. If the discontinuity is non-fitting, the factor Rl = 0.75.
The first term rough, smooth, or polished is established by feeling the surface of the discontinuity
; rough hurts when fingers are moved over the surface with some (little) force, smooth feels that there is resistance to the fingers, while polished gives a feeling about similar to the surface of glass.
The second term is established visually. 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. The two terms of visual and tactile give a combined term and the corresponding factor is listed in table 1.
The visual part of the roughness small scale (Rs) contributes only to the friction along the discontinuity if the walls on both sides of the discontinuity are fitting, i.e. the asperities
on both discontinuity walls match. If the discontinuity is non-fitting, the visual part of the roughness small scale (Rs) should be taken as planar for the calculation of the sliding-angle, and hence, the roughness small scale (Rs) can be only rough planar, smooth planar, or polished planar.
This is further sub-divided in coarse, medium, and fine for the size of the grains in the infill material or the size of the grains or minerals in the discontinuity wall. The larger of the two should be used for the description. The thickness of the infill can be very thin, sometimes not more than a dust coating.
The sliding criterion is a tool to estimate easily the shear strength
Shear strength (discontinuity)
The shear strength of a discontinuity in a soil or rock mass may have a strong impact on the mechanical behavior of a soil or rock mass. The shear strength of a discontinuity is often considerably lower than the shear strength of the blocks of intact material in between the discontinuities, and...
properties of a discontinuity
Discontinuity (geotechnical engineering)
A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
in a rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
mass based on visual and tactile (i.e. by feeling) characterization of the discontinuity
Discontinuity (geotechnical engineering)
A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
. The shear strength of a discontinuity is important in, for example, tunnel
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...
, foundation, or slope
Slope stability analysis
The slope stability analyses are performed to assess the safe and economic design of a human-made or natural slopes and the equilibrium conditions. The term slope stability may be defined as the resistance of inclined surface to failure by sliding or collapsing...
engineering, but also stability of natural slopes
Slope stability
The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock...
is often governed by the shear strength along discontinuities.
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
Tilt test (geotechnical engineering)
In geomechanics a tilt test is a simple test to estimate the shear strength parameters of a discontinuity. Two pieces of rock containing a discontinuity are held in hand or mounted in test equipment with the discontinuity horizontal. The sample is slowly tilted until the top block moves...
but on a larger scale. The sliding criterion has been developed for stresses that would occur in slopes between 2 and 25 m, hence, in the order of maximum 0.6 MPa. The sliding criterion is based on back analyses of slope instability and earlier work of ISRM and Laubscher. The sliding criterion is part of the Slope Stability Probability Classification
Slope stability probability classification
The slope stability probability classification system is a rock mass classification system for slope engineering and slope stability assessment...
(SSPC) system for slope stability analyses.
| characterization | factor | ||
|---|---|---|---|
| Roughness large scale (Rl) | wavy | 1.00 | |
| slightly wavy | 0.95 | ||
| curved | 0.85 | ||
| slightly curved | 0.80 | ||
| straight | 0.75 | ||
| Roughness small scale (Rs) | rough stepped/irregular | 0.95 | |
| smooth stepped | 0.90 | ||
| polished stepped | 0.85 | ||
| rough undulating | 0.80 | ||
| smooth undulating | 0.75 | ||
| polished undulating | 0.70 | ||
| rough planar | 0.65 | ||
| smooth planar | 0.60 | ||
| polished planar | 0.55 | ||
| Infill material (Im) | cemented/cemented infill | 1.07 | |
| no infill - surface staining only | 1.00 | ||
| non-softening & sheared material, e.g. free of clay, talc | coarse | 0.95 | |
| medium | 0.90 | ||
| fine | 0.85 | ||
| softening & soft-sheared material, e.g. clay, talc | coarse | 0.75 | |
| medium | 0.65 | ||
| fine | 0.55 | ||
| gouge < irregularities | 0.42 | ||
| gouge > irregularities | 0.17 | ||
| flowing material | 0.05 | ||
| Karst (Ka) | none | 1.00 | |
| karst | 0.92 | ||
Sliding-angle
The sliding-angle is calculated as follows:
-
- sliding-angle in degrees
- Rl = roughness large scale
- Rs = roughness small scale
- Im = infill material in the discontinuity
- Ka = karst; presence of karst (solution) features along the discontinuity
(The values for the parameters are listed in table 1 and explained below)
Roughness large scale (Rl)
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 discontinuityDiscontinuity (geotechnical engineering)
A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
with the example graphs in figure 1. This results in a descriptive term: wavy, slightly wavy, curved, slightly curved, or straight. The corresponding factor for Rl is listed in table 1.
The roughness large scale (Rl) contributes only to the friction along the discontinuity when the walls on both sides of the discontinuity are fitting, i.e. the asperities
Asperity (geotechnical engineering)
In Geotechnical engineering the term asperity is mostly used for unevenness of the surface of a discontinuity, grain, or particle with heights in the range from approximately 0.1 mm to many decimetre...
on both discontinuity walls match. If the discontinuity is non-fitting, the factor Rl = 0.75.
Roughness small scale (Rs)
The roughness small scale (Rs) is established visually and tactile (by feeling).The first term rough, smooth, or polished is established by feeling the surface of the discontinuity
Discontinuity (geotechnical engineering)
A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
; rough hurts when fingers are moved over the surface with some (little) force, smooth feels that there is resistance to the fingers, while polished gives a feeling about similar to the surface of glass.
The second term is established visually. 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
Discontinuity (geotechnical engineering)
A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
is compared with the example graphs in figure 2; this gives stepped, undulating, or planar. The two terms of visual and tactile give a combined term and the corresponding factor is listed in table 1.
The visual part of the roughness small scale (Rs) contributes only to the friction along the discontinuity if the walls on both sides of the discontinuity are fitting, i.e. the asperities
Asperity (geotechnical engineering)
In Geotechnical engineering the term asperity is mostly used for unevenness of the surface of a discontinuity, grain, or particle with heights in the range from approximately 0.1 mm to many decimetre...
on both discontinuity walls match. If the discontinuity is non-fitting, the visual part of the roughness small scale (Rs) should be taken as planar for the calculation of the sliding-angle, and hence, the roughness small scale (Rs) can be only rough planar, smooth planar, or polished planar.
Infill in discontinuity (Im)
Infill material in a discontinuity has often a marked influence on the shear characteristics. The different options for infill material are listed in table 1, and below follows a short explanation for each option.Cemented discontinuity or cemented infill
A cemented discontinuity or a discontinuity with cemented infill has higher shear strength than a non-cemented discontinuity if the cement or cemented infill is bonded to both discontinuity walls. Note that cement and cement bounds that are stronger than the surrounding intact rock ceases the discontinuity to be a mechanical plane of weakness, and, hence, the 'sliding-angle' has no validity.No infill
No infill describes a discontinuity that may have coated walls but no other infill.Non-softening infill
Non-softening infill material is material that does not change in shear characteristics under the influence of water nor under the influence of shear displacement. The material may break but no greasing effect will occur. The material particles can roll but this is considered to be of minor influence because, after small displacements, the material particles generally will still be very angular. This is further sub-divided in coarse, medium, and fine for the size of the grains in the infill material or the size of the grains or minerals in the discontinuity wall. The larger of the two should be used for the description. The thickness of the infill can be very thin, sometimes not more than a dust coating.Softening infill
Softening infill material will under the influence of water or displacements, attain in lower shear strength and will act as a lubricating agent.This is further sub-divided in coarse, medium, and fine for the size of the grains in the infill material or the size of the grains or minerals in the discontinuity wall. The larger of the two should be used for the description. The thickness of the infill can be very thin, sometimes not more than a dust coating.
Gouge infill
Gouge infill means a relatively thick and continuous layer of infill material, mainly consisting of clay but may contain rock fragments. The clay material surrounds the rock fragments in the clay completely or partly, so that these are not in contact with both discontinuity walls. A sub-division is made between less thick and thicker than the amplitude of the roughness of the discontinuity walls. If the thickness is less than the amplitude of the roughness, the shear strength will be influenced by the wall material and the discontinuity walls will be in contact after a certain displacement. If the infill is thicker than the amplitude, the friction of the discontinuity is fully governed by the infill.Flowing material infill
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.).See also
- Discontinuity (Geotechnical engineering)Discontinuity (geotechnical engineering)A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
- Shear strength (Discontinuity)Shear strength (discontinuity)The shear strength of a discontinuity in a soil or rock mass may have a strong impact on the mechanical behavior of a soil or rock mass. The shear strength of a discontinuity is often considerably lower than the shear strength of the blocks of intact material in between the discontinuities, and...
- Slope stability probability classificationSlope stability probability classificationThe slope stability probability classification system is a rock mass classification system for slope engineering and slope stability assessment...
(SSPCSlope stability probability classificationThe slope stability probability classification system is a rock mass classification system for slope engineering and slope stability assessment...
) - Tilt test (Geotechnical engineering)Tilt test (geotechnical engineering)In geomechanics a tilt test is a simple test to estimate the shear strength parameters of a discontinuity. Two pieces of rock containing a discontinuity are held in hand or mounted in test equipment with the discontinuity horizontal. The sample is slowly tilted until the top block moves...