PERMFILE55017

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 3/24/2004
• Doc Name: Section 11
• Section_Exhibit Name: Volume VII Geotechnical Studies
• Media Type: D
• Archive: No

infilling material, roughness, •
intact rock, and water q
conditions are among those that ~ ~
may be considered. The larger /
the DSI, the greater the ~~ ~~
possibility of failure along cwc_~u„
that discontinuity given an
unfavorable geometry, as g "°°•`~"
explained later. Zn other ;
words, the DSI calculations
combine several important ~J
characteristics to create a -~ vu„e /
,,
single value useful for °~•^• »•••••M~^o
comparing the importance of """°' •~"~••
discontinuities to one another. C
Figure 8 shows the general form '(/,1
of Watts' DSI equation. The
complexity of the equation makes "'mac` `~~--~
it impractical to calculate all
of the DSI values for large data D
sets by hand. Computers handle ~~~
it easily however. The ~ ~•,'
derivation is treated in detail ~ \
by Watts and West (1986) . ,ova„c ``/ •
Although based on limiting '11'
e q u i l i b r i u m t h e o r y, giqure 7. Types of rock slope
discontinuity significance is failures and stereoplots of pole
not meant to replace safety cluster orientations likely to
factor calculations. The produce them. (From Hoek and
indices provide a means of
quickly ranking discontinuities Bray, 1981.)
so that the more significant
ones may receive greater attention. The significance values are
intentionally independent of slope orientation, so that they may
be of use before slope alignment is selected.
DSI values may be plotted on either rectangular dip plots or on
stereonets. Data from Cedar Bluff, Virginia illustrate the DSI
concept. Figure 9 is a plot of the maximum calculated DSI values
occurring at each orientation on the plot. It is similar in
appearance to a population glot which shows the number of
discontinuities in the data set at each orientation. However, the
numbers here represent the highest DSI values at each orientation.
In terms of population, Cluster 3 would be deemed most important
as the field data show it to contain 35 discontinuities. Cluster
4 would be next in importance, containing 25, followed by Cluster
1, containing 16 discontinuities. However, failures involving the
discontinuities of Cluster 4 would require the shearing of
considerable intact rock, as the site investigation revealed those
joints to be short and poorly connected. Hence, Cluster 4 is not •
as significant to the stability of the slope as its population
might indicate.
Stereonet Analyses 8 ~ Appendi% A
/'~R ~y
APPRoveO 3/a~I~oy