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2014-03-07_REVISION - M1988112 (2)
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2014-03-07_REVISION - M1988112 (2)
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Last modified
8/24/2016 5:40:49 PM
Creation date
3/10/2014 10:19:29 AM
Metadata
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Template:
DRMS Permit Index
Permit No
M1988112
IBM Index Class Name
REVISION
Doc Date
3/7/2014
Doc Name
Tailing dam report TR33
From
DRMS
To
McClure & Lobato
Type & Sequence
TR33
Email Name
WHE
GRM
Media Type
D
Archive
No
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Step 3: Develop Failure Event Trees and Probability Estimates <br />All plausible PFMs assigned to Categories I or II (Table 3) were then carried forward for risk <br />analysis. Probability estimates were assigned to each step involved in the initiation and <br />progression to failure. Probabilities for initiation and each step towards progression were <br />estimated using as guidance empirical tabulations for similar failure mechanisms that have been <br />developed by the U.S. Bureau of Reclamation, U.S. Army Corps of Engineers and others, as <br />documented in the recently updated manual of Best Practices in Dam and Levee Risk Analysis <br />(USBR, 2012). The process described as follows results in a calculation of annualized failure <br />probability. The annualized failure probability W is defined as the product of the load <br />probability (PL) times the probability of failure under the load (PF), as follows: <br />f = PL X PF <br />1. The annual load probability (PL) is typically included at the beginning of the event tree. <br />For purposes of flood loading, the PMF is assumed have a recurrence interval of 100,000 <br />years. This corresponds to an annual load probability of 1X 10 -5. <br />2. The probability for each subsequent event on an event tree is then estimated. The value <br />Of PF will be computed as the product of probabilities assigned for each node on event <br />trees leading to dam failure. To simplify the process, for some nodes the estimated <br />probability was assigned based on subjective descriptors as summarized on Table 4. <br />Table 4 Descriptive Probabilities <br />Descriptor <br />Probability <br />Virtually certain <br />0.999 <br />Very likely <br />0.99 <br />Likely <br />0.9 <br />Neutral <br />0.5 <br />Unlikely <br />0.1 <br />Very unlikely <br />0.01 <br />Virtually Impossible <br />0.001 <br />Table 4 is derived from USBR (2012) Chapter 13 — Subjective Probability, Table 8 -2 available at: <br />http: / /www. usbr. jzov/ ssle/ damsafety/ RiskIBestPractices/ 13- SubiectiveProbabiliU20121116. pdf <br />San Luis Project Miller Geotechnical Consultants <br />Tailing Dam Data Report 38 February 2014 <br />
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