72 monitoring prisms set across the dam wall and on the dam crest next to the overflow gates. 48 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.
In total, data from 479 sensors is pulled into the Trimble monitoring software. Because the data can be collected and correlated in one plat- form, today’s dam engineers have a much better understanding of the structure’s history and transitions over time. Improved monitoring leads to enhanced analysis With the implementation of an automated monitoring system, Victoria Dam engineers now have a much more comprehensive and accurate collection of movement data at their fingertips. The team can focus their efforts on detailed analysis, predicting future behavior and con- tinually studying the behavior of the dam with the added security of the system’s automated alarm system that alerts them to any changes to the dam exceeding set thresholds. The real-time, and now accurate, data allows the team to determine temperature and water level effects, and their influence on temporary movements, as well as permanent deformations. Among other observations made since the adoption of Trimble equipment, the team has noticed irreversible swelling of the concrete of the dam, which will continue to be observed. Commenting on the new monitoring system post-installation, Er. Arru- pola observed, “Working with Trimble’s automated, real-time geodetic GNSS monitoring data, combined with automated water level read- ings, has enabled us to establish a more complete and more accurate method for monitoring movement, reservoir crest levels and possible swelling of the Victoria Dam.”
GNSS and water level monitoring—setup of GNSS receivers and piezometers To provide redundancy to prism monitoring and to monitor the stabil- ity 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 observa- tion 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 log- ger of the piezometers sends new data sets once per hour. Bringing it all together—Trimble 4D Control monitoring software The heart of the monitoring system is Trimble 4D Control monitoring software. Victoria Dam project leaders decided to install Trimble 4D Control on a server in the dam’s control center. The software processes data from optical total stations, GNSS receivers, geotechnical and other types of sensors. The historic monitoring data was imported into the software to analyze the behavior of the dam since it was erected. The manually collected historic data, the new real-time raw data, as well as the processed results allow project engineers to apply additional, customized calculations to the sensor data.
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csengineermag.com
august 2020
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