| Though digital photos are routinely taken for slope inspection along national road in Hokkaido、 they are not systematically applied for the prediction、 location or volume estimation of failures. The authors made the applicability study for such digital photos for road slope management. For the purpose、 two methods were studied. One is a background differencing technique in which changes are identified by superimposing photos taken by digital camera with the same angle in different times. Another is a variation measuring technique in which temporal changes are checked using terrain models prepared by a 3D-photo measurement system. Obtained results were as follows. (1) Though photographing positions are marked with paint or guide piles、 it is occasionally lost by snow fall and sediment cover or deleted paint. To clarify the allowable error for the cases、 we took a series of photos of which the photographing position was intentionally moved from the true point for a slope of 60m distance. As a result、 difference identification was found to be possible when the distance moved was until 10m. (2) To examine the accuracy of failure location、 photos were taken five times over a period of two years and three months for a slope of abandoned road where rock falls frequently have occurred. As a result、 many true rock falls were distinguished as the differences identified by the background differencing technique by eliminating those caused by change of light and vegetation. (3) To estimate the failure volume of a slope、 photogrametry was used to make terrain models from several photos、 and the failure volume was calculated as 57m3 from the difference between prepared terrain models before and after the failure. |
