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Summer 2002
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In Japan, GIS Helps Assessment of Asphalt Deterioration for Dam and Reservoir Construction

With its excellent waterproof property, asphalt has been widely used in a variety of construction fields such as road and building infrastructure construction and, especially, dam and reservoir construction. However, longtime exposure to sun and weathering causes numerous wrinkles and fissures to appear on the surface of the asphalt mastic at the top of the asphalt facings, causing deterioration that leads to numerous problems.

 
Numerous wrinkles and fishures on the asphalt surface are quickly extracted as ArcView polyline data.

Near the Kizyou town, Miyazaki Prefecture of Japan, the Kyushu Electric Power Cooperation, Inc., is constructing the Ommaru water pumping storage power generation station high on Dyama Mountain. A large water reservoir will be constructed and asphalt concrete will be used as a waterproof coat on the reservoir surface.

When in operation, the reservoir water level will be lower in the daytime due to power generation, and the asphalt mastic on top of the asphalt facing will undergo natural weathering and deterioration. This deterioration is a serious issue for both safety and power generation. Is there a way to quickly diagnose the aging condition of the asphalt mastic?

Researchers from the power cooperation are taking digital photographs of the asphalt mastic at different times while under intense sun and accelerated weathering conditions. The photos can then be used to identify the pattern of wrinkles and fissures and analyze the relationship between their distribution patterns and the strength and permeation of the asphalt mastic. A series of laboratory and field observation tests has been conducted and much data obtained.


A large water pump storage power generation station is now under construction near the Kizyou town, Miyazaki Prefecture of Japan.
 

For this procedure to be effective, it was necessary to create a method of converting the results (e.g., the identified wrinkles and fissures captured on the digital photos) into vector data.

The research group of the Kyushu Electric Power Cooperation, Inc., chose the Spatial Analyst extension of ArcView to establish a quick way to diagnose the asphalt coat aging problem. Because the red-green-blue (RGB) color index for wrinkles and fissures is different from the other aspects of the asphalt, it was possible to extract the wrinkles and fissures from the picture. An ArcView extension was developed using Avenue, the ArcView development language, for automatic identification implementation.

This ArcView extension uses four steps: picture load, data conversion, wrinkle area identification, and wrinkle polyline extraction. All the digital photo pictures are loaded into ArcView and then converted to GIS grid data. By simply using the computer mouse to click on specific wrinkles or fissures on the screen, the value for wrinkles and fissures can be automatically determined.

This is similar to the method called "supervised classification" in the remote sensing process. After the value for a wrinkle or fissure is determined, the area can be identified and the central line is then extracted using the thin process and converted into a polyline. The length and area of the wrinkle are calculated and added as the attribute of the polyline. Finally the polyline data is sent to another analysis program called "fractal analysis" to find the characteristic value of the wrinkles/fissures distribution pattern being studied.

The relationship between the wrinkle distribution pattern and the strength and permeation of the asphalt coat has been established based on test data from field observation and the laboratory.

In practical use, a digital photo is snapped when the reservoir water level becomes lower, recording the surface condition of the asphalt mastic. By using the ArcView extension, the complicated wrinkle distribution can be quickly extracted and analyzed for its characteristic value. From a relationship curve thus derived, the strength and permeation index of the weathered asphalt mastic can be automatically determined. This ArcView diagnosis method provides a convenient and effective way for helping manage the daily safety of the dams and reservoirs.

For more information, contact Toshiharu Sasada (e-mail: toshiharu_sasada@kyuden.co.jp) or Guoyun Zhou (e-mail: zhou@ies.kyushu-u.ac.jp).

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