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中国三峡地域では、ダム貯水による斜面変動が活発になっている。本研究では，貯水による斜面安定性への影響を解明するために，活発的に変動している樹坪地すべりにおいて，伸縮計を用いて斜面変動の連続観測を行なった。地下水存在状態を解明するために，1m深地温探査を行った。その結果、斜面内部の地下水の分布は斜面変位に直接関係していることは分かり、また、計13台の伸縮計の観測結果より，斜面変動の様子が概ね把握できた。, The Three Gorges Dam construction on the Yangtze River in China is the largest hydro-electricity project in the world. After the first impoundment in June 2003, many landslides occurred or reactivated. Shuping landslide is one of the most active landslides among them. In this paper, the deformation of the Shuping landslide monitored by GPS, extensometers, and crack measurements are summarized. Also, for the investigation of the groundwater situation, 1m-depth ground temperature measurement was conducted, and the groundwater veins were estimated. Based on the monitoring data and exploration results, a deformation model of the landslide caused by impoundment of reservoir was proposed.

To estimate chemical weathering rate of granitic rocks, natural waters in a very smallbasin in the Rokko mountains have been collected weekly over a six-year period (1980-1985). The XRD indicates that kaolinite is the main product of plagioclase alteration inthe weathered granitic rocks. The water compositions are plotted in the field of stabilityof kaolinite in a phase diagram for the system Na-SiO2-Al2O3-H2O. This fits the XRDevidence that the main product phase is kaolinite, and it indicates that solution/kaoliniteequilibrium may play a role in controlling the water compositions. The amount of kaoliniteproduced by CO2-bearing water reacting with granitic rocks is estimated as 35.1 g/m2/year, and the total amount of weathering rocks is estimated as 55.3 g/m2/year.

The variation with time in the concentrations of dissolved chemical species and the dischargeof ground waters in the Kushibayashi area, Shiga Prefecture were investigated from Oct. 1972 toNov. 1973 in order to obtain the basic data for estimate of the amounts of clay minerals produced byweathering processes through the chemical compositions of ground waters in this area.The authors have examined the relationships among the chemical species contents of the waters, and between the chemical species contents and discharge of the waters. And the following have beenattained: (1) A clear negative relationship is observed between sulfate and bicarbonate contents inthe waters drainaged from the layer about 5 m depth under ground surface, (2) a good correlationis observed between discharge and bicarbonate and sodium contents, respectively, and (3) the trans-ported amount of bicarbonate ions increases with an increase in discharge but suddenly the increasingrate of transported amount changes after a definite discharge and the slpoe in the graph trends tobecome steep in the order 1 m, 5 m, and 10 m depths under ground surface.A hypothesis on the mechanism of this phenomenon is also presented.

In order to estimate the partial pressure of dissolved carbon dioxide gas in natural watersof landslide areas, the following approximate formula is obtained: log Pco2='log〔HCO3￣〕 -pH+7. 8 at water temperature range, 0-30°, by using hydration equilibrium of carbondioxide gas and the first dissociation equilibrium of carbonic acid, and assuming that individualion activity coefficients are unity. The authors have examined the relationships among thecalculated dissolved carbon dioxide gas, bicarbonate contents and pH in the ground watersampled from various landslide areas. The following have been obtained: (1) The modevalue of partial pressure distribution of carbon dioxide gas is found at 10~ atmosphere inlandslide areas, but at 10-3. I atmosphere in granitic areas, (2) A possibility of distinctionbetween stream and ground water from water quality is found by using a pH-HC03-Pco2diagram, and (3) The solubility of biotite, chlorite, Ca-feldsper and K-mica is oversaturatedwith respect to that of calcite in landslide areas.

The landslide at the Otobaru area, Beppu City, occurred twice in 1943 and 1969. A partof this area, even now, is affected considerably by thermal activities.Variations in chemical and isotopic compositions of waters from the Otobaru area and itsvicinity were investigated from 1977 to 1983 and 1986 to 1987.The results are as follows: (1) electric conductivity data suggest that the two kinds oflow-concentration water and high-concentration water exist in the landslide area, (2) theexistence of two groundwater aquifer in the landslide area and its vicinity is inferred fromtritium data, (3) variations in chemical composition of waters from the horizontal borehole areaccompanied by the rise and decline of water table, (4) the waters from the landslide area andits vicinity are in equilibrium with montmorillonite, (5) the most waters under 10 1 atm. Of Pco2are saturated or supersaturated with calcite, and (6) there is no detectable contribution ofgeothermal water to the waters from the landslide and its vicinity.And our hypothesis on the mechanism for the formation of calcium sulfate type water isalso presented.

In this paper we describe an experimental study on the behavior of the groundwater inthe Kamisaga landslide area, Tokushima Prefecture, Shikoku District. The investigations havebeen carried out since 1974 and still are continued. The points of discussion about thevariation of the groundwater in this landslide area are as follows;1) the actual conditions of the water bearing stratum, 2) the variation of the groundwater level on the rainfall, 3) the variation of the discharge from the ground on the rainfall, 4) the volume fluctuations of the actual water bearing mass, 5) the volume of drain water effective for prevention of landslide.

In the first report1) we discussed on the behavior of the groundwater in the Kamisaga land-slide area. In this paper we describe the same points of discussion about the variation of thegroundwater in this landslide area from a few experimental data on 1977. The results in agreementwith the those of the first report were obtained experimentally. The correlation was observedbetween the volume fluctuation of the actual water bearing mass and the 7 days rainfall.

The electric prospecting was conducted through the vertical sounding, based on the electricresistivity methods which consist of three-electrode, four-electrode and Schiumberger methods.The results are summarized as follows.1) The results of vertical sounding are unable to discriminate of the geology composed of baserock and detrital material layer in the shattered zone type landslide area.2) The relationship between the ground water level and the resistivity value are not recog-nized obviously.3) Landslide surface is detected by internal strain-meter in several depth and also electric dis-continuity layer is divided into several layers composed of different resistivity values. Accor-dingly, it seems that the discussion of the relationship between discontinuity of electric resistivityand landslide surface is meaningless.4) The influence of rainfalls is not clearly shown to the resistivity values of grounding elec-trode.

地すべり移動と地下水は密接な関係があり, 地下水の合理的な調査法を見出すことは重要なことである・現在地すべり地の地下水を調査する方法は, 薬品を用いた地下水追跡法であるが, 既設ボーリソグや湧水点間の流通を確認して地下水経路を推定するのが最も一般的に用いられているようである。この方法によれば地すべり地内のボーリング孔・湧水点の数によって調査地域が限定され・地すべり全域にわたる地下水の情報を得るのは困難である。地すべり全域にわたる地下水の情報をうる手段があれば・さらに精査する場合や排水工事を行う場合の有力な指針になるであろう。地すべり全域にわたる地下水の情報を得る手段は現在開発されつつあるがP, 筆者等はこの方法とは別に, 電気探査法を利用して, 地すべり地の地下水について清報がえられるかどうか検討した結果, ある程度のことが解ったので報告する。, The low apparent resistivity values according to the distribution map in landslideareas detained by the horizontal exploration using the resistivity method were consideredto be a locality containing underground water in the tertiary type landslide areas. Thelow apparent resistivity values were measured to be under 30 (2-in according to be datawich which the writers got by resistivit metod.This locality containing underground water in landslide area will contribute to theprecious underground water serveys, what we call tracer method; underground waterlogg, when we obtain the information of the underground water in landslide areas.

We have investigated conditions of underground water streaming in the MataunoyamaLandslide area by tracer method, but we do not get the information on systematic undergroundwater vein. Then, as one of the methods for this problem, we carry out the undergroundwater survey by the horizontal measurements of underground temperature distribution.As the result of it, information on systematic underground water vein is gotten.In view of this fact, we consider that the method is useful for underground water veinsurvey.

It was cleared by the existing investigated results that the underground water was existent asthe vein-stream condition in and around the landslide area. By the results, the author was awarethat it was very difficult to obtain the information which was concerned with the existent locationof the underground water vein-stream using the present tracer method. As it was considered agood method that the existent location of the underground water vein-stream was assumed inadvance before earring Out the present tracer method, and the presnt tracer method was carried out, the author try to use the underground temperature survey which utilized at the hot-spring surveyaccording to assumed the existent location of the underground water vein-stream. By the results, itwas cleared that this survey method obtained excellent results.

Ground water flow may be generated in sloping soil layer laid on semi-pervious rock surfacewhen the infiltration of rain water exceeds in the downward leakage of water out of rock surface.This flow brings about the increase of shearing stress and decrease of compressional stress betweensoil particles through the drag force in the direction of flow and pressure gradient of pore water, respectively, and may result in slope failure. This paper is a theoretical report considered aboutthis type of failure. Taking account of the distribution of stress force, sloping layer is divided intotwo region, the one is upper layer (I) in wet condition due to the infiltration and the other is lowerone (II) influenced by ground water flow. According to the Mohr's theory of failure, the forma-tion of slip surface may be initiated in the layer (II) if it is occurred. At first, the necessary condi-tion of its formation is considered and, secondly, the drawing method of slip line is derived in activeand passive failure based on the conception of the limiting state of static equilibrium.

The variations with time in the concentrations of dissolved elements and the discharge of theground waters in the Kamenose landslide area in Osaka Prefecture were investigated from July 1972to January 1973 in order to obtain the basic data for the study of estimate of the amounts of clayminerals produced by weathering processes through the chemical compositions of ground waters inthis area.The authors have examined the relationships among the chemical species contents of the waters, and between the chemical species contents and discharge of them. The following have been attain-ed: A clear negative relationship is observed between sulfate and bicarbonate contents, a clearpositive relationship between ea]cium and bicarbonate contents in the waters of the drain tunnel, sul-fate content increases and bicarbonate content decreases with the increasing discharge of bore holewaters in the tunnel at high altitude, and the concentrations of sulfate and bicarbonate ions werescarcely changed in spite of the increasing discharge at low altitude.

The authors have carried out hydrological survey and chemical analysis of groundwaters in the Matsushiro landslip area from September 1966 to October 1967.Water balance and chemical composition of the waters in the area show that the groundwaters are gushing not from the deep origin and not affected by precipitation.There are several types of time change in the chemical composition characteristic ofspecified regions, but there is a general tendency that the concentration of CaCla increasedmost remarkably with time.