ML19290D520
| ML19290D520 | |
| Person / Time | |
|---|---|
| Issue date: | 11/29/1979 |
| From: | Schmitt T NRC OFFICE OF STANDARDS DEVELOPMENT |
| To: | Odonnell E NRC OFFICE OF STANDARDS DEVELOPMENT |
| References | |
| CON-NRC-01-78-004, CON-NRC-1-78-4, TASK-OS, TASK-SS-802-9 NUDOCS 8002220096 | |
| Download: ML19290D520 (2) | |
Text
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November 29, 1979 NOTE T0:
Edward O'Donnell FROM:
Thomas Schmitt
SUBJECT:
FLORIDA STATE UNIVERSITY DRAFT REPORT ON A CHARACTERIZATION AND CLASSIFICATION OF GE0 LOGIC FAULTS IN THE APPALACHIAN FOLDBELT In response to your request I have reviewed Florida State University's Draft Report. Because of time constraints my comments are limited to the section entitled, " Critical Need for In-Situ Measurements" (Appendix A).
The use of in-situ stress measurements is certainly one of the most promising techniques in the field of tectonics. However, the appendix as written is a bit over :implified in that a casual reader could come to believe the state-of-ti,e-art is considerably more evolved than it presently is. Some specific iomments follow:
1.
Strain relief methods are not constrained to shallow depths. They can be made in tunnels, mines, etc.
In this case, they may be as, or more reliabit than hydrofracturing. The Germans (Illies & Greiner, et.al.)
have qui e successfully applied the technique in deep quarries. They have compared the results with hydrofracturing (Rummel) and deep mines and found excellent agreement.
2.
The French (Paquin, et.al.) have had success with flat jack measureme'ts, which is not mentioned.
3.
The various problems associated with residual, topographic, and thermal stresses are not mentioned. These factors certainly effect strain relief measurements and in some cases hydrofracturing.
4.
There are a number of problems with hydrofracturing concerning pre-existent fractures.
Hast, in a recent review cited earlier work indicating that fracturing can be induced by drilling.
Furbtar problems with pumping rate, particularly in porus media can develop.
5.
Extreme care must be used in evaluating the apability of a fault or fault zone on the basis of a few in-situ stress measurements.
Even if the stress at a point is estimated precisely, the value may not be indicative of the active regional field. A 15 degrees or so deviation can easily be induced due to stress concentrations at the end of a fault, or perhaps around a rigid or soft inclusion, 3uch as an intrusive body. Combine this with measurement uncertainties and serious errors can occur.
The authors do not make this point strongly enough.
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2-6.
In-situ stress measurements are extremely useful, but they are not a cure all. Given the present state-of-the-art they should be used in conjunction with other lines of investigaiton.
Given the problems with the strain relief, flat jack, and hydrofracturing techniques, a better estimate of the stress at a point might be made by a combination of two or more of the techniques. At least if they agree then one has more confidence in the values.
Because it is unlikely they would err in the same way.
7.
It is noted that this section of the draft report is not intended to be a treatise on stress measurements. However, given the importance that the authors give to such techniques, then more background information is warranted.
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Thomas Schmitt Site Safety Standards Branch 4
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