Environmental Engineering Reference
In-Depth Information
400
Crotty
Very high strength rock, well compacted
Medium to high strength rock, well compacted
Gravels, well compacted
Reasonable compaction
350
Aguamilpa 3A
300
250
Medium to high strength rock
E
rc
113 e
(
0.0052 D80)
Very high strength rock
E
rc
9.0
10
5
. D
80
1.70
R
2
0.83
200
R
2
0.44
Murchison
150
Golillas
Cethana
100
Reece
Bastyan
50
Little Para
Salvajina 3B
Scotts Peak
0
0
50
100
150
200
250
300
350
400
450
D
80
(particle diameter equivalent to 80 percent passing)
Figure 15.11.
Representative secant modulus of compacted rockfill at the end of construction E
rc
versus
rockfill particle size and rock unconfined compressive strength. (Hunter 2003; Hunter
and Fell, 2002, 2003c).
(c) To account for the non linearity of the stress-strain relationship for rockfill, estimates
of modulus for stress levels less than or greater than the representative E
rc
are done by:
- For very high strength rockfills apply a linear correction of
7.5% per 200 kPa to
the E
rc
estimated from Figure 15.11 for a vertical stress of 1400 kPa. Apply positive
corrections for decreasing stresses and negative corrections for increasing stresses.
The applicable range is 400 kPa to 1600 kPa.
- For medium to high strength rockfills apply a linear correction of
6% per 200 kPa
to the E
rc
estimated from Figure 15.11 for a vertical stress of 800 kPa (applicable
range is 200 kPa to 1200 kPa).
(d) For medium strength (UCS 6 MPa to 20 MPa) rockfills apply a multiplication factor
of 0.7 to the E
rc
value determined from the equation for medium to high strength
rockfills.
(e) Tangent moduli can be estimated from the secant moduli after correction for the stress
levels.
The following points should be noted:
-C
u
, the uniformity coefficient for the particle size distribution curve, is implicitly
allowed for in the D
80
value. Generally, decreasing C
u
is observed for increasing D
80
;
- For materials placed with larger rollers (eg. 13-15 tonne deadweight vibrating rollers)
the data does not indicate an increase in moduli for the greater compactive effort. This
may be due to greater material breakdown under the heavier rollers and a resultant
reduction of D
80
;
- For weathered rockfills the intact strength will be lower than for fresh rock, which will
result in a decrease in secant moduli, but this will be countered by the greater break-
down in particle size, which will give an increase in moduli associated with a reduction
in D
80
;
- If testing on the proposed rockfill material indicates a significant reduction in UCS on
wetting is likely and only limited water has been, or is proposed to be, used in construc-
tion, the rockfill is likely to be more susceptible to settlements on wetting due to rainfall
and flooding. There is insufficient data to advise on how to quantify this settlement;
