Safety of Existing Dams Evaluation and Improvement (1983) / Chapter Skim
Currently Skimming:
10. Instrumentation
10. Instrumentation
Pages 278-308
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 278... ...
The means and methods available to monitor geotechnical phenomena that can lead to a dam failure extend over a wide spectrum of instrumentation devices, consisting of very simple to very complex ones. The program for dam safety instrumentation requires detailed design that is consistent with all other project components; it must be based on prevailing geotechnical conditions of the dam and impoundment site and on the hydrologic 278
|
From page 279... ...
While instrumentation can be tied to automatic warning systems, the experience of the committee indicates that no computer or automatic warning system can replace engineering judgment. Instrumentation data must be carefully reviewed periodically by an engineer experienced in the field.
|
From page 280... ...
c~ 4o Id cd o ¢ En Id o . ct ~ o ~ - ~' ~ a o ~ 'e ~ i: 'e s~uoulamseay~ IIBJUIB s~uacuamseay~ alLuslaS amsSald aced pub alla s~uaUuaaeldsla IE]
|
From page 281... ...
281 rid rid I_ ~ rid X X XX ~ rid rid r~ ~ ~ X r~ r~ r~ r~ r~ X X X X X X X X X X X X X ~ X X X X X X XX CO ~V ~ ~ ~ o ~ o o o ~ o ·to ~ E o a o ~ 3 Ct o ~o .= ~ o C)
|
From page 282... ...
Drainage Systems In many concrete and masonry dams a foundation drainage system is installed to reduce uplift pressures on the dam. These systems are usually installed during construction but can be installed or supplemented at any time.
|
From page 283... ...
Packers can also be used within the holes with connected gages to isolate the interval in which the measurement of water pressure is desired. Observations of the reservoir and tailwater elevations should be recorded when uplift pressures are measured.
|
From page 284... ...
To be effective, these records should be continuous and periodically reviewed by a professional engineer versed in the design and vulnerability of embankment structures. These reviewers should be able to distinguish the important indicators from the unimportant.
|
From page 285... ...
For existing dams monumentation to measure movements is usually limited to the crest and downstream slopes. The monuments usually consist of steel rods or surveyor's markers imbedded in concrete placed in excavations on the embankment and abutments.
|
From page 286... ...
Water pressures in the embankments are measured by piezometers. There are basically three types of piezometers in common usage: (1)
|
From page 287... ...
In large structures there may be several lines of piezometers, while in smaller structures and existing dams perhaps one line would be adequate. The time interval between measurements of the water levels or pressures in piezometers depends on the age and condition of the structure.
|
From page 288... ...
The reduced data must be reviewed periodically by a professional engineer or engineering geologist with expertise in slope stability. Another excellent reference on instrumentation to monitor ground movements relative to slope instability is by
|
From page 289... ...
discuss the need for seismic instrumentation and recommend the minimum instrumentation for recording basic earthquake data. They recommend that where there may be potential for determining if earthquakes are induced from reservoir loading a network of seismographs should be in operation prior to impounding the reservoir.
|
From page 292... ...
~ I .b o ._ 4— c~ x LLJ oo z ~ o - c~ c~ ~ ~ c~ ~ o o v, ~ 3 C)
|
From page 293... ...
1 ~ 1 ~ I :~ ) Throat ~ Section Crest - ~ I ~ ~ , )
|
From page 294... ...
For seismographic characteristics, Bolt and Hudson recommend two alternative schemes that will meet the minimum requirement and that have been field tested. One system uses portable seismometers and visual recording units; the network stations are not connected.
|
From page 295... ...
A timely reference is Geotechnical Instrumentation for Monitoring Field Performance (National Research Council 1982~. Chapter 5 of that report presents numerous instrumentation types and installation procedures.
|
From page 296... ...
lI. Maihak, 2000 Hamburg, 39 Semper Street, Hamburg, West Germany (NA suppliers: Ampower Corporation, 1 Marine Plaza, North Bergen, NY 07047 and Roctest, Ltd.)
|
From page 297... ...
76: Instrumentation of Earth and Rockfill Dams (Earth Movement and Pressure Measuring Devices) ; Chapter 2, Movement Devices for Embankments and Foundations.
|
From page 298... ...
Sonic devices have been used effectively to locate leaks in dams. They have been particularly useful in measuring leakage through the concrete facings of rockfill embankments where disruption of the slab joints or cracks in the panels were primary sources of leakage.
|
From page 302... ...
The processing of large masses of raw data can be efficiently handled by computer methods. The interpretation of the data requires careful examination of measurements as well as other influencing effects, such as reservoir operation, air temperature, precipitation, drain flow and leakage around the structure, contraction joint grouting, concrete placement schedule, seasonal shutdown during construction, concrete testing data, and periodic instrument evaluations.
|
From page 303... ...
The reading of these instruments should continue for years to establish performance during operation. Figure 10-9 shows a plot of horizontal displacements versus pool levels at El Infiernillo Dam (Marsal and de Arellano 1972~.
|
From page 304... ...
304 o ._ Cal 4= a)
|
From page 305... ...
Data from earth pressure cells ShOUlCt ne rectuceu ano time blots maintained for each cell during and after construction. Analysis of data should inclucle a comparison of observed earth pressure with earth pressure assumed for the design of the structure.
|
From page 306... ...
The frequency of collection and evaluation of data is also discussed in detail for each category. Some excellent illustrations concerning dam foundation uplift pressure histories, methods of showing uplift pressure gradients, typical deflection history, and typical precise alignment marker layout and details can be found in the U.S.
|
From page 307... ...
RECOMMENDED READING ASCE (1981) Conference Proceedings on Recent Developments in Geotechnical Engineering for Hydro Projects, Fred Kulhawy, ed.
|
From page 308... ...
(1976) "In-Situ Pore Pressure Measurements at Rio Blanco," Journal of the Geotechnical Engineering Division, ASCE, Vol.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.