Environmental Engineering Reference
In-Depth Information
Figure 6.35.
Robertson and Campanella's (1984) method for estimating
for cohesionless soils from
the cone penetration test (CPT).
Normal compaction of granular filters in dams e.g. 4 passes of a 10 tonne smooth drum
vibratory roller, in layers 500 mm compacted thickness, should give a relative density of
at least 70%, so the effective friction angle should be around 38° for fine sand and 40° for
well graded filter sands and sandy gravels.
In reality at low confining stresses e.g. less than 200 kPa,
is likely to be 2° to 5°
higher than these figures. If the figures become critical to the stability analysis, they
should be checked by laboratory testing.
6.1.10
Shear strength of partially saturated soils
See Section 11.2.4 for a discussion on this topic.
6.1.11
Shear strength of rockfill
The shear strength of rockfill is dependent on the effective normal stress, and to a lesser
extent on the bulk dry density, void ratio or degree of compaction; the unconfined com-
pressive strength of the rock, the uniformity coefficient of the grading, maximum grain size,
fines content, and particle shape (Marsal, 1973; Douglas, 2003).
Table 6.4
summarises the
effect of these variables.
Figure 6.36
shows the methods for representing the shear strength.
Douglas (2003) carried out an extensive analysis of the factors affecting the shear strength
of rockfill. This involved establishing a large database from published and unpublished tri-
axial testing, and statistical analysis.
