Dr. NGUYEN Anh Dung, VSSMGE
Before the 1960s, most of the constructions in Vietnam were small- to medium-size scale subjected to low to medium loading conditions; consequently, monitoring work was not paid much attention and limited to mainly topographic surveilling. It is possible that the first proper monitoring equipment was installed in Vietnam during the construction of the hydroelectric dam in Thac Ba, Hoa Binh. It was a simple Casagrande piezometer utilized to monitor ground water level at the downstream slope or at the low permeability core of the dam.
From the 1990s, as the economy in Vietnam has grown rapidly, numerous large scale constructions such as skyscrapers, mega dams, large factories, and highways were and will be built on various ground conditions. Design and construction of foundation structure for the modern infrastructures, buildings etc become more and more challenging as they not only grow in scale (e.g. height, depth and area) but also locate in complicated grounds such as soft soils, fractured weathered rock, in seismic areas etc. To meet the increasing demand of modern constructions, innovative foundation techniques as well as sophisticated quality assurance and quality control system are required. To the present date, monitoring work becomes an essential requirement during construction and operation of major structures.
In Vietnam, monitoring system is probably most utilized on dams of reservoir for hydroelectric plants and irrigation structures in which various types of monitoring equipment are used. The types of reservoir dams constructed in Vietnam are rather diverse including earth fill dams, concrete face rockfill dams, concrete dams, roller compacted concrete dam, and arch dam. For dam structures, monitoring during operation is as crucial as monitoring during construction to detect any abnormality and then prevent dam failures.
Monitoring equipment is diverse, ranging from the simplest type such as standpipe piezometer, settlement plate, inclinometer etc to more complex electrical or magnetic types such as vibrating wire indicator, convergence meter, tiltmeter, magnetic extensometer, MEMS, VW Data Recorder etc. Horizontal movement of the dam crest is automatically monitored using Robotic Total Station equipment. There are several well-known producers of monitoring equipment in the world, such as Geokon, Roctest, RST, Slope Indicator, ACE Instruments… Monitoring for small structures with short construction time and a small number of monitoring equipment is typically carried out manually with portable readout unit. However, for medium to large structures with long construction / operation duration, numerous amounts of monitoring equipment and fast recording cycle, measurement data are automatically collected and delivered to a centralized system using fiber optic or Wi-Fi for a convenient manner of management and assessment. Currently, Vietnam has one collection center (ADAS) which belongs to Vietnam Electricity Corporation (EVN) to store data from the five hydroelectric power plant located in the Northwest provinces, including Hoa Binh (1.900 MW), Son La (2.400 MW), Lai Chau (1.200 MW), Huoi Quang (520 MW) and Ban Chat (220 MW), with about 3000 sensors connected to an automatic recording system with monitoring frequency of 1 observation per hour.