地すべり地における地表変位測量デ-タを用いた円弧すべりの解析
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概要
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Recent field surveying technique composed of electro-optical distance-meter and theodolite has enabled rapid and precise measurement of distant objects. To apply this technique to landslide monitoring, i. e., displacement observation of marked objects in landslide area, surveying station is constructed on safe and stable ground apart from the landslide realm. At this station, main terrain of the landslide should be observed, and surveying of the marked objects is carried on with an interval of several days or weeks corresponding to velocity of the landslide movement.<BR>Change of three dimensional coordinates of the marked objects is furnished by succeeding surveyed data, so that behaviour of the landslide is detected by trajectory of marked objects on a horizontal or several vertical planes. Observing trace of each marked point on the horizontal projection plane, areal extent and main moving direction of landslide is distinguished. On a vertical projection plane parallel to the main moving direction, entire traces of marked points are examined.<BR>When the traces show a tendency of concentric circles, we can treat the landslide as rotational movement. To find rotational center of concentric circles on the vertical projection plane, two analytic approaches, geometrical method and least square method are considered. In numerical analysis, least square method shows better convergence than geometrical method, but the latter has simplicity in computation.<BR>In general, on vertical projection plane parallel to main moving direction of rotational landslide, shape of sliding surface analogizes with circle. Then using the above mentioned center of concentric circles and an obvious position of failure on main sliding surface, head scarp, toe buldge, sheared position in borehole etc., a circle is drawn on the vertical projection plane, which shows projected shape of main sliding surface of the landslide.<BR>As an applicative example, landslide occurred at Komoro in Nagano prefecture in August, 1981 is analyzed, and remarkable notes are stated.
- 公益社団法人 日本地すべり学会の論文