Civil Engineering Reference
In-Depth Information
400
Clay infilling
Fault gouge,
shear zones,
low strength rock
Range of values
10
13
300
1
14, 20
9
200
5
26
3
21
24
22
19
6
100
18
3
4
15
4
25
16
9
7
12
11
5
7
24
2,11
1
18
23
17
8
10
20
30
40
Friction angle (degrees)
1. Bentonite shale
2. Bentonite seams in chalk
3. Bentonite; thin layers
4. Bentonite; triaxial tests
5. Clay, over consolidated
6. Limestone, 10-20 mm clay infillings
7. Lignite and underlying clay contact
8. Coal measures; clay mylonite seams
9. Limestone; <1 mm clay infillings
10. Montmorillonite clay
11. Montmorillonite; 80 mm clay seam in chalk
12. Schists/quartzites; stratification, thick clay
13. Schists/quartzites; stratification, thick clay
14. Basalt; clayey, basaltic breccia
15. Clay shale; triaxial tests
16. Dolomite, altered shale bed
17. Diorite/granodiorite; clay gouge
18. Granite; clay-filled faults
19. Granite; sandy-loam fault fillings
20. Granite; shear zone, rock and gouge
21. Lignite/marl contact
22. Limestone/marl/lignites; lignite layers
23. Limestone; marlaceous joints
24. Quartz/kaolin/pyrolusite; remolded triaxial
25. Slates; finely laminated and altered
26. Limestone; 10-20 mm clay infillings
Figure 4.14
Shear strength of filled discontinuities (modified from Barton, 1970).
ranging from about 25 to 45
◦
, and cohesion
values ranging from 0 to about 100 kPa. Fault
gouge derived from coarse-grained rocks such
as granites tend to have higher friction angles
than those from fine-grained rocks such as
limestones.
shear strength with displacement. In conditions
where there is a significant decrease in shear
strength with displacement, slope failure can
occur suddenly following a small amount of
movement.
Filled discontinuities can be divided into two
general categories, depending on whether there
has been previous displacement of the discon-
tinuity (Barton, 1974). These categories are fur-
ther subdivided into either normally consolid-
ated (NC) or over-consolidated (OC) materials
(Figure 4.15):
Some of the tests shown in Figure 4.14 also
determined residual shear strength values. It was
found that the residual friction angle was only
about 2-4
◦
less than the peak friction angle, while
the residual cohesion was essentially zero.
Shear strength-displacement behavior is an
additional factor to consider regarding the shear
strength of filled discontinuities. In analyzing
the stability of slopes, this behavior will indic-
ate whether there is likely to be a reduction in
•
Recently displaced discontinuities
—These dis-
continuities include faults, shear zones, clay
mylonites and bedding-surface slips. In faults
and shear zones, the infilling is formed by
