ML19308B106
| ML19308B106 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 07/05/1967 |
| From: | NATHAN M. NEWMARK CONSULTING ENGINEERING SERVICES |
| To: | |
| Shared Package | |
| ML19308B102 | List: |
| References | |
| NUDOCS 7912120830 | |
| Download: ML19308B106 (2) | |
Text
G yK s
NATHAN M. WEWMARK CONSULT 1NG ENGINEERING SERVICES
Subject:
Submerged Weir in Intake Canal Duke Power Company Document Nos. 50-267/270/287 The following was transmitted by telephone July 5,1967, and will be docu-mented by letter to Dr. Morris.
Tne following report is based on the studies made by Dr. A. J. Hendron, Jr.
of our staff and has been approved by Dr. W. J. Hall and myself. Our com-ments concerning the stability of the proposed submerged weir, as described in Supplement 5 of Amendment 5, by Item No. 11 dated 16 June 1967, follow:
(1) The f actor of safety for static i,'havior under rapid drawdown, within the pressure level of interest, as stated in the report is consistent with i
the shear strength of the material equal to or greater than that correspond-I ing to a Mohr f ailure envelope with a cohesion intercept of 280 psf and an angle of internal friction of 30, for consolidated-undrained conditions.
These material properties appear to be reasonable. However, the test tech-nique used may not be entirely adequate since there may be a possibility of incomplete saturation of the samples because they were not '_'back-pressured" to assure 100% saturation, immediately before shearing. Nevertheless, from the results of our calculation, there appears to be no cause for concern.
(2)
For combined earthquake in rapid drawdown, the effective shearing resistance of the dam on sloping surfaces is about 0.09 W, where W is the weight of the sliding wedge. Although this is slightly less than the maxi-mum earthquake accelerntion of 0.10 g, for a consistent value of maximum ground velocity of 5 inches /second, the maximum sliding displacement of each of the sloping surfaces is estimated to be less than 0.4 inches. Even for a larger carthquake, the amount of motion under earthquake conditions appears to be relatively small or negligible.
(3)
It appears that the static stability and the resistance to piping are the major problems in relation to possibilities of instability. Another major concern is the possibility of erosion of the downstream sloping surface if local settlements of the crest could occur causing high velocity local flows if the weir is overtopped. A special spillway section could avoid this difficulty.
(4) Avoidance of erosion due to overtopping is also possible through use of riprap of adequate thickness and size of stone.
This should be placed on j
a filter layer of ' thickness adequate to insure that the continuity of the filter will not be interrupted. It may not be possible to have this assurance with only a 12-inch thickness of filters unless there is careful inspection during construction.
I y
t 49121s0 $3C#
e
_ o....
l' e
j (5) To avoid piping and to ass te downstream stability under steady-state scepage, a base drainage filter and toe drain is usually required. Although this is not shown in Amendment No. 5, it is our understanding that such a drain and filter _ of lengths about 1/3 the base width of the weir will be used.
This will probably-be adequate.
(6) Although no specific foundation treatment is indicated beyond the removal of alluvial materials, it appears to us that the foundation will present no problem from_the point of view of large amounts of scepage or stability against i
earthquake motion of the intensity considered possible in the application.
)
/
s
]~
s.
_