Customer Stories

Optical monitoring—setup of prisms and robotic total stations Because of the double curvature of the Victoria Dam wall and often rainy conditions in the area, installing the required monitoring instrumentation across the dam was quite challenging. To start, the team had to develop a safe method to install the instrumentation, which included the construction of a gantry-like system suspended from a crane. This setup allowed an engineer to reach the wall of the dam safely to install the components, even at its most concave shape. The team installed 72 monitoring prisms set across the dam wall and on the dam crest next to the overflow gates. Forty-eight of these prisms were placed at the same locations as the pre-existing survey targets, and 24 were added at new locations. In addition to the prisms at the dam, 40 prisms were installed on the left bank of the dam and 32 on the right bank. During installation, the team also set up 64 millimeter (2.5 inch) prisms as part of the control network for the Trimble total stations, comprised of four points per station. The Trimble S9 total stations collect data measurements automatically for consistent and reliable data capture of all movement across the dam. Today, the total stations are scheduled to take a two-face observation of all prisms every three hours, which takes approximately 20 minutes. The collected data is then sent to Trimble 4D Control software for processing, analysis and visualization. GNSS and water level monitoring—setup of GNSS receivers and piezometers To provide redundancy to prism monitoring and to monitor the stability of the control network, GNSS monitoring was integrated into the system. The team installed three Trimble NetR9 Ti-M GNSS receivers on the dam crest and one as a base station in the control center building. For integrated data processing, each GNSS antenna is co-located with a prism. All GNSS receivers on the dam crest transmit the observation data to the control center over Wi-Fi with a backup power source completing each GNSS station. Amongst other sensors, the team also incorporated vibrating wire piezometers and a wireless data logger system to automatically read water levels. The wireless data logger transmits readings from close to the center of the dam crest to the control center building where the server hosting the system's monitoring software is located. Currently, the GNSS processing interval is set to three hours, while the data logger of the piezometers sends new data sets once per hour. "We selected existing monitoring station pillars on opposing banks for the new total stations to make sure all parts of the dam wall could be monitored, even when the overflow gates are open. We couldn't risk not being able to obtain a reading due to cascading water." "The Victoria Dam is a vital piece of Sri Lanka's infrastructure in terms of providing irrigation, electricity generation, and the sustainability and prosperity of the region. The new, automated monitoring system brings together all the data sources we need to focus on long-term structural stability of the dam and to study the behavior of the structure in accordance with its original design."

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