2015-02-26_REPORT - C1982056 ‎(3)‎

• Permit No: C1982056
• IBM Index Class Name: Report
• Doc Date: 2/26/2015
• Doc Name: Foidel Subsidence Evaluation Part 3‎(Final)‎
• From: DRMS
• To: Nicole Caveny
• Type & Sequence: PR10
• Permit Index Doc Type: Subsidence Report
• Email Name: JLE
• Email Name: DIH
• Media Type: D
• Archive: No

Table 1: Summary of Scanline Survey Data
Scanline
(length in ft)
Joint
Set
Number of
Joints
Apparent Spacing
(ft)
Alpha
(degrees)
Terzaghi
Corrected
Spacing (ft)
1 (600)
S l
51
11.8
36
9.5
S3
28
21.4
76
5.2
2 (560)
S l
19
29.5
77
6.6
S3
54
10.4
20
9.7
S4
42
13.3
15
12.9
3 (440)
S 1
14
31.4
75
8.1
S3
59
7.5
20
7.0
S4
52
8.5
15
8.2
4 (420)
Sl
18
23.3
75
67
S3
49
8.6
20
8.1
S4
39
10.8
15
10.4
Using true spacing, all three -set block- forming
combinations of joint sets S1, S2, S3 and S4 were
analyzed to obtain the frequency distribution of
block sizes. Experience has shown that many
discontinuity sets have a spacing distribution that
approximates reasonably to a negative exponential
form (Priest and Hudson, 1976, Priest and Hudson,
1981), and this was assumed to apply in this study.
The negative exponential distribution is a single -
parameter distribution that is completely defined by
its mean, so provided the mean spacing is known,
the full range of probabilities can be estimated.
Analysis of the bedding plane data indicated a
lognormal spacing distribution. Using these distribu-
tions, the potential discontinuity combinations and
resulting block sizes were analyzed using
probabilistic modeling software.
The results of this analysis, in the form of a
cumulative probability distribution, are presented in
Figure 2, together with the cumulative distribution of
block sizes from the boulder catalog. The results are
in good agreement, and converge well in terms of
the larger block sizes. Based on this analysis, a worst
case block size of about 6000 cubic feet was
considered appropriate for Phase I rockfall hazard
assessment. An 'equivalent' disk, with a diameter of
26 ft, a thickness of 11 ft, and a volume of 5840 cu.
ft. was used in the CRSP3 runs.
Prior to the main hazard assessment, a number of
trial runs were carried out to calibrate the CRSP3
model, and select appropriate site - specific slope
surface parameters. These calibration runs were
carried out on sections of the slope where previous
rockfalls provided a basis for comparing observed
and predicted behavior.
Typical block sizes were determined from the
boulder catalog for each calibration section. These
block sizes were converted to equivalent disks or
cylinders for input to the CRSP3 model, by setting
the diameter equal to the average of the two most
similar dimensions, and the thickness or lengths
equal to the remaining dimension.
2.3 Crsp3 Parameters
CRSP3 requires that the surface of the modeled
profile be described in terms of tangential and
normal (restitution) coefficients. Tables 2 and 3
show the relationship between the surface descrip-
tions presented by Pfeiffer and Bowen (1989) for
assigning tangential and normal (restitution)
coefficients, and inferred equivalent site conditions.
Table 4 indicates the ranges for these parameters
considered appropriate at this site.