Dam Instrument/ Bendungan
WELL-PLANNED AND IMPLEMENTED MONITORING IS AN ESSENTIALCOMPONENT OF SUCCESSFUL DAM CONSTRUCTION AND OPERATION. DAM MONITORING IS SUBJECT TO NUMEROUS REGULATIONS AND IN MANY COUNTRIES IT IS REGULATED BY STRICT ADMINISTRATIVE STANDARDS.
The primary function of monitoring is to ensure the longevity and safety of a dam. Monitoring must enable the timely detection of any behavior that could deteriorate the dam, potentially result in its shutdown or failure, in order to implement corrective measures. Monitoring also plays a fundamental role during construction. It enables the verifi cation of design hypotheses and may affect the construction rate of certain works. Monitoring is particularly crucial during the initial filling of the reservoir, a critical phase in the life of a dam.
INSTRUMENTATION: THE KEYSTONE OF MONITORING
Instrumentation is used to accurately quantify certain parameters of structural behavior over time and to monitor their rate of change. Selection Criteria for Instrumentation Three major criteria guide instrument selection:
- Reliability of the measurements obtained (accuracy, resolution, precision and drift)
- Instrument longevity, supported by numerous references
- Ease of readout automation, essential for efficient data collection and interpretation
Monitoring involves numerous steps including direct or remote visual inspection as well as topographical
measuring and instrumentation.
The scope of the monitoring methods employed depends on the potential risk associated with dam and
Such characteristics include:
- Dam height and type
- Extent of potential damage to people and structures located in fl ood zone
- Reservoir and spillway capacity
- Site seismicity
- Foundation weakness zones
Types of Measurement
The types of measurement to be carried out as well as instrument location must be selected according to the particular conditions of the foundation and of the dam itself. Nonetheless, there are certain general guidelines to follow for instrumentation selection.
The following are the main points to verify:
- Relative impermeability between the foundations and reservoir perimeter
- Cutoff structure effi ciency
- Efficiency of the downstream drainage networks
These behaviors can be monitored with the following instruments:
- Flow meters
Settlement and horizontal deformation behavior can be evaluated once measurements are complete. Particular attention must be paid to zones where signifi cant differential settlement could lead to fi ssuring in the structure.
- Borehole extensometers
- Settlement gauges
Instruments used for monitoring potential shear zones:
- In-place inclinometers
Monitoring Instruments for Specifi c Applications In addition to offering a complete line of monitoring instruments for new dams, Roctest Telemac designs and builds instrumentation equipment for existing dams and adapts these instruments to specific applications.
Many instruments are designed to be installed while a dam is under construction and cannot be incorporated into existing works. This poses a problem mainly for concrete dams with fi ssuring problems.
The instruments used include the following:
For Crack Opening Variations
- Single-point or triaxial surface-mount jointmeters, such as the RTF, which can be installed under water on the upstream side of the dam.
- BOF-EX borehole extensometer
For Variations in Stress and Temperature
- CIUS instrumented cylinder
- VBS stress meters
DESTRESSING A DAM BY SAWING
Dam-sawing techniques have been developed to solve the problem created by the swelling of old concrete due to the reaction between certain cements and aggregates. Roctest Telemac has designed customized instrumentation based on the BOF-EX borehole extensometer and stress variations measurement to monitor stress release and internal deformations provoked by the saw-cut.
IMPROVING STABILITY OR HEIGHTENING A CONCRETE DAM
Improving stability or heightening a concrete dam requires the installation of permanent high-capacity tieback anchors. To monitor these anchors, Roctest Telemac has designed high-capacity vibrating wire load cells. Tailing Dams
Tailing dams constructed with hydraulic fi ll are built near the equilibrium limit and require close monitoring. The main measurements required for dam stability analysis and slide prevention are pore pressure, settlement and lateral deformation.
- Settlement gauges
- Inclinometer probes and in-place inclinometers
Automated Data Acquisition and Processing
The collection and analysis of large quantities of data, especially over long distances, requires centralized and automated measuring techniques. Results are more accurate and data can be processed more rapidlythus enabling efficient alarm systems to be implemented when predetermined thresholds are exceeded. It is practically impossible to consider the instrumentation of a major dam without automated data acquisition systems. Roctest Telemac’s SENSLOG allows economical data logging and can be readily connected to multi-node networks for real-time monitoring. Data acquisition centers are easily user-confi gured through a highlevel “soft” instrument control language. This language supports full diversity in connected device types, measurement intervals, data conversion, statistical processing, and strategies for alarm control, and logging.