Measuring up: seismic monitoring of dams

Despite progress in the dynamic analysis of dams, it is still not possible to reliably predict how they will behave during very strong ground shaking due to difficulty in modelling their inelastic behaviour, and insufficient information on the spatial variation of ground motion. However, the factors that eventually lead to failure, as well as their severity and effect on the structure, can be measured and monitored with seismic instrumentation and monitoring systems. Each dam is unique, and the monitoring system should be tailored accordingly.

Deploying strong motion accelerometers and data acquisition systems in a dam helps to detect exceedance of allowed performance criteria as well as to identify and verify structural behavior. Utilising seismic instrumentation and monitoring systems, timely notifications about any potential problems can be generated and behavior of the dam can be monitored. 

For over 50 years Kinemetrics says it has been providing seismologists and structural engineers with earthquake instruments, systems and solutions to effectively monitor dams. One of the company’s comprehensive solutions is in the form of the KMIDam. This is an infrastructure management system that provides a data centre operating a network of smart, IP-ready, seismic stations. These high performance and compact accelerographs leverage the latest technology to deliver maximum flexibility and scalability. They can be operated as stand-alone free field stations or as a network of several stations that are linked via wireless technology for common trigger and can be configured as real-time or event triggered systems. The data centre is a real-time data acquisition system that provides information to an operator in real-time or on-demand. This will give full command and control of the stations, alarm system notification, and automatic processing for reporting.

KMIDam also offers a post event dynamic analysis for engineering purposes and possible detection of change in behaviour of the dam structure after a natural hazard event. The system issues an alarm based on the instrumentally recorded acceleration threshold exceedance for operational purposes. This helps to reduce both risks and costs, and can help avoid an actual disaster with a smart notification system, which allows initiation of early damage detection to help save lives and assets. Here are a few examples of dams instrumented by Kinemetrics.

Calaveras Dam, California, US

In conjunction with Terracon, Kinemetrics has successfully fabricated a turn-key system for Calaveras Dam.

The dam has four monitoring points at the crest, foundation, abutment and free-field with the integrated instrumentation and software of the multi-sensor seismic network producing high-quality information.

The system consists of a network of smart, IP-ready seismic stations combined with a data center for extensive dam monitoring. Spread spectrum radios provide telemetry, 90W solar panels power the stations, and Kinemetrics’ RockMonitor professional software monitors all stations in parallel.

Ruskin Dam, British Columbia, Canada

Ruskin Dam is a concrete gravity dam on the State River in Ruskin, British Columbia, Canada. It was completed in 1930 for the primary purpose of hydroelectric power generation. In 2017, Kinemetrics supplied and installed seismic instrumentation for this dam, including Obsidian recorders, world-standard Episensor ES-T and SBEPI (Shallow Borehole Episensor). There were four Obsidian 4-ch recorders, which were connected to the Episensors, as well as an Obsidian 8-ch recorder, which was interfaced to one ES-T and one SBEPI. They were installed in ?ve different locations, which included the dam gallery, left abutment, right abutment and two control rooms.

Upon installation, the dam staff were fully trained by Kinemetrics to successfully operate and maintain the system.

Multi dam implementation in Thailand

The Electricity Generating Authority of Thailand (EGAT) is Thailand’s leading state-owned power utility under the Ministry of Energy and responsible for electric power generation and transmission for the whole country. It owns and operates different power plants at 45 sites across the country, and this includes 24 hydropower plants. EGAT also owns and operates a high voltage transmission network which covers all parts of the country.

Kinemetrics, through its operator representative AES, has designed a seismic monitoring system across seven EGAT dams. Each dam has instrumentation of four short-period stations for induced seismicity and three or four accelerographs (Basalt) at the crest, toe, abutment, and about 2km downstream. The local data acquisition is performed with Rockhound platform and the central data acquisition with the Antelope platform installed on 2 Dell servers running RHEL. 

The Aspen System at the headquarters of EGAT in Bang Kruai District, north of Bangkok, acquires all data in real-time. The system is tuned to carry out automatic location of small local events near each dam and regional events. The system automatically calculates the peak ground acceleration (PGA). In addition, a new event triggers a custom process that creates event ?les for each station including PGA calculation. Antelope distributes an e-mail that contains all event information including PGA, PGV, PGD plus the links to the event ?les.

Real time response spectra are calculated and if any of the three curves crosses the top lines, an alarm will be issued.