| Summary: | 碩士 === 國立成功大學 === 土木工程學系專班 === 91 === This research implemented a measure device to survey the slope at Jia-Xian ~ Tian-Chi section of the southern cross-land highway. Totally we selected 47 appropriate locations as the measure points to install these devices which were safe, economical, quick-installed and easy-maintained. Passing through the rain season from May to September in 2002, these devices got the accurate occurring time of the slope failure caused by the rain wash. Totally we got the data, occurring time of slope-failure, from 25 locations. These slope failures all belonged to the small scale of the shallow layer failure. Comparing the Central Weather Bureau’s rainfall data and our occurring time of the slope failure, it revealed that there was the close relation between the shallow layer failure and the rainfall situation.
The result revealed:
(1) The slope failures happened for 1 ~ 2 times at 25 out of 47 measure points, so that the total frequency counted to 32 times. Among these happenings, there were 17 slope failures occurred within 2 hours after the highest rainfall intensity occurred. It was 53% among total slope-failure frequency. Within 2~5 hours after the highest rainfall intensity occurred, there were 7 slope failures happened; it occupied 22%. Beyond 5 hours after the highest rainfall intensity occurred, there were 8 slope failures happened; it was 22% among the total frequency. This result was the same as 池谷浩’s research.
(2) The failures whose slope angles were above 70 degrees occurred 13 times; it was 40.6% among the total happenings. The failures whose slope angles were between 60 and 70 degrees occurred 10 times; it was 31.2%. The failures whose slope angles were between 50 and 60 degrees occurred 9 times; it was 28.2%. It revealed that when the rain fell, the slope was steeper, the slop failure happened easier.
(3) When the accumulation of rainfall depth was within 80mm, the slop failure happened 23 times; it occupied 51.06% among totally slope-failure happenings. It revealed that at the southern cross-land freeway, the probability of slope-failure occurrence was high if the rainfall depth reached 80mm at the slope of high potential failure.
(4) When the highest rainfall intensity reached 20mm/hr, there were probably a half of slopes failed. It showed that the probability of slope failure occurrence was high if the rainfall intensity reached 20mm/hr at the slope of high potential failure.
(5) Classifying the type of stratum among the 32 slope failures, the slope type belonged to the sandy-shale layer was 18; it was 56% among the total. The slope type belonged to the sandy layer was 7; it occupied 22%. The slope type belonged to the shale layer was 7; it also occupied 22% among the total.
(6)The failure of slop happened 17 times within 2 hours after the highest rainfall intensity occurred. In these failure happenings, the failures whose slope angle above 70 degrees occupied 8 out of 17 times, and the percentage was 47%. The failures whose slope angles between 60 and 69 degrees happened 4 times; it was 23.5%. The failures whose angles between 50 and 59 degrees happened 5 times; it was 29.5% among the total happenings. It showed that after a torrential rain, the slope was steeper, the slope failure happened easier.
(7) We put the data of all measure points in a coordinate plane which was used the highest rainfall intensity as the y-coordinate and rain depth accumulation as the x-coordinate. From the plane, we chose 40mm as the rain depth accumulation and 20mm/hr as the highest rainfall intensity to create a linear equation: y + 2x = 40. Except one extraordinary point, all data points were located above this line in the coordinate plane. Hence, it was the critical line of shallow layer failure at Jia-Xian ~ Tian-Chi section. On the other hand, this critical line would be a criterion for announcing the road-damage warning.
(8) In this survey, we also considered the distance between slop-failure measure point and the rainfall observatory. The distance within 5 km was 56.5% among the total. The distance between 5 km and 10 km was 41%. The distance above 10 km was 3%. Therefore, the reliability of data was higher if the distance between the measure point and the observatory was within 10 kilometer.
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