A STUDY ON INVESTIGATIONS OF THE MECHANISM OF HOT-SPRINGS LANDSLIDE OCCURRENCE

在大分县别府市，涌现出了大量喷泉质量和氛围特别好的温泉，泉源（洞）达2847个，日流量达13.7040万升。因此，别府市是温泉观光胜地，无论是源的数量，还是排放量都在日本名列前茅。豆瓣区是著名的酸性硫化氢喷泉和绿转喷泉温泉区。但是，该地区是一个温泉滑坡区，从其特殊的地质特征条件和附近地区所谓的solfatic粘土的组成来看，该地区的滑坡活动。由于处于温泉区的特殊环境，地下水的pH值、温度等性质与一般滑坡区有很大的不同，即使进行对策研究，也需要引起重视。此外，在对滑坡边坡进行稳定性检测时，采用经验法是目前的一种状态。在此基础上，对Myouban滑坡区进行了现场调查，明确了温泉滑坡的发生机理，并在影响滑坡稳定性的因素中采用不同的边坡稳定性分析和强度参数，计算了该滑坡的安全系数。得到的结果如下所示。1)地下水位变化大，全年上升幅度尤其大，至雨季及6月中旬开始的9月台风期上升幅度较大。2)地下水处于高温、低pH、高电导率等高腐蚀环境下，且随钻孔不同趋势不同。3)滑移面附近的粘土接受不同季节水温、pH、电导率的变化历史，其变化范围为水温24 ~ 29℃，pH3 ~ 4.5，电导率10 ~ 30ms /m。4)用反计算法计算强度参数时，下滑移面下，“费勒纽斯法”得到的内摩擦角ⅱ比Bishop法的内摩擦角ⅱ增大约1.3℃。少

A lot of hot springs where the fountain quality and atmosphere were especially done spring up in Beppu City, Oita Prefecture, and the numbers of sources (hole) are 2, 847-places and amount of discharge is 137, 040 kiloliters a day. Thus, Beppu City is hot-spring sightseeing spot of the top of Japan in both, the numbers of sources, and amount of discharge. Myouban district is a famous hot-spring area in the acid hydrogen sulfide fountain and the green turn fountain. But, that area is a hot-spring landslide area where the landslide activity is seen from having peculiar geological features condition, and the composition of a near region of a so-called solfataric clay. Properties of groundwater including the pH and the temperature are greatly different from usual landslide areas because it is under a peculiar environment of hot-spring area, and even if it undertakes the examination of the countermeasure, the attention is required. Moreover, when the stability of the landslide slope is exam … More ined, it is a current state that experienced method is used.Then, we performed the site investigations at Myouban landslide area to clarify the occurrence mechanism of the hot-spring landslide and calculated the safety factor of the landslide using different slope stability analysis and strength parameters in factors influenced on the landslide stability.The result of obtaining is shown as follows. 1) The groundwater level is large the change, and rises especially greatly through year until the rainy season and the typhoon time of September from the middle of June. 2) Properties of groundwater are under the high corrosion environment like a high temperature, a low pH, and a high electric conductivity, etc., and the tendency is different according to the bore hole. 3) Clay in the vicinity of the slip surface receives the history of a different water temperature, the pH, and the electric conductivity by the season, and the range is water temperature 24-29℃, pH3-4.5, and electric conductivity 10-30mS/m. 4) When having calculated the strength parameters by the back calculation method, the internal friction angle ¢ obtained by the "Fellenius method" grows by about 1.3℃ than the ¢ of the Bishop method under lower slip surface. Less