An automated monitoring system, optical total stations, GNSS receiv- ers and other structural monitoring instrumentation continuously monitors Sri Lanka’s tallest dam — providing a 360-degree view in real-time — of all dam movements. Victoria Dam is the tallest dam in Sri Lanka, located on the Mahaweli River and about 20 kilometers (12 miles) from the town of Teldeniya. A double-curvature concrete arch dam, it is vital to the area in terms of agricultural irrigation and the production of hydroelectric power. Con- struction of the dam started in 1978 and was completed in April 1985. Challenge Due to the age of the dam and its importance to the infrastructure of the country, the Mahaweli Authority of Sri Lanka determined the dam’s original monitoring system required a major upgrade. Authori- ties needed continuous monitoring capabilities to analyze the structural integrity of the dam, as well as to understand its behavior according to the dam’s original design. The team investigated modern structural monitoring technology and ultimately selected Trimble sensors and Trimble 4D Control software to build a sophisticated motion monitor- ing instrumentation network. The crown jewel of Sri Lanka dams Considered by many as the crown jewel of Mahaweli Development Projects, the Victoria Dam is built in a deep valley just above the Vic- toria Falls rapids and 300 meters (984 feet) below the point where the Hulu Ganga river meets the Mahaweli River. At the time of its original construction, the dam’s funding, design, and the technical expertise was provided by the United Kingdom. Then Prime Minister Margaret Thatcher was at the dam’s ceremonial opening in 1985 along with then-president of Sri Lanka, J. R. Jayewardene. The dam is 520-meters long and 122-meters high (1,706-feet long by 400 feet high) and has a width of six meters (19 feet) at the crest and 25 meters (82 feet) at the base. Water from the dam is fed to a powerhouse via a 5,646 meter (18,523 foot) tunnel. From there, tanks feed three 70 megawatt, 12.5 kV turbines, which produce up to 780 gigawatt hours of electrical energy annually (roughly 6 percent of Sri Lanka’s power). The dam creates the Victoria Reservoir which has a gross storage ca- pacity of 722,000,000 cubic meters. (Source: Amazing Lanka ). The region where the dam is located has periods of extreme rainy seasons, which can dramatically impact reservoir water levels to po- tentially unsafe tolerances. When the dam was originally constructed, engineers installed a comprehensive monitoring system that included a geodetic system and instruments embedded into the dam’s structure. Monitoring tasks were conducted manually, including the geotechnical Comprehensive Monitoring of Victoria Dam Modern Monitoring of Victoria Dam Performed by Sri Lanka Authorities Using Trimble Monitoring Solutions
sensors that were surveyed by staff every two weeks and the geodetic points, which were measured and recorded on an annual basis. Original monitoring equipment shows its age Over the years, some of structure’s original measurement equipment stopped working properly, parts became unserviceable, and the ac- curacy of the data produced was compromised. Er. S.R.K. Aruppola, Director of Operation and Maintenance for Victoria Dam, explains the dam’s conventional manual geodetic measurement processes were becoming tedious and dangerous to manage as the terrain is steep and slippery. Measuring and recording the dam’s movement with these in- struments was also prone to human error, requiring the team to fix each instrument on four different pillars and take multiple sets of readings at separate intervals. Adding concern, minor cracks in the dam were found in 1996. After consulting with technology specialists, the dam’s director and his team began designing a fully-automated, real-time geodetic sys- tem to replace the manual monitoring system. The new monitoring system is comprised of several components, including Trimble NetR9 Ti-M GNSS receivers and GNSS antennas, Trimble S9 robotic total stations, Trimble DiNi digital precise leveling instruments, automated water level reading systems and the integration of other geotechnical instrumentation. In addition to these components, all movement sen- sors were designed to connect to the core of the monitoring system — Trimble 4D Control monitoring software. Trimble 4D Control software collects, processes, visualizes and analyzes the data of all monitoring sensors installed at the Victoria Dam and populates the results in real-time through an intuitive web interface. The software also issues alarms automatically whenever the system detects movement outside of user determined, acceptable parameters and sends status reports at user defined intervals. 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 instru- mentation 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
13
august 2020
csengineermag.com
Made with FlippingBook Annual report