The deformations on the cut slope of road have been surveyed in the Chichibu Tertiary basin.These are caused by the mechanical weathering on the slope surface.Consequently, the slope surface recedes in parallel or inclines steeply and it has been in an unstable condition for a long period. The process of the recession can be connected with the number of years since the formation of the cut slope according to the rock types respectively.Further, in the model experiment by means of sand slope, the process could be observed continuously.Moreover, it was found that the various mechanical properties and weathering properties of rocks were in close relation to each other.
There are two types of groundwater in the Korea.One is the groundwater containedin the unconsolidated rock system, the other is the groundwater existing in the consolidated rock system.In this report only the latter type of groundwater is discussed. Geologically the Korean Peninsula is a part of Continental China.In terms of geogical time the ages concerned with the formation of sedimentary rocks range from the Pre-Cambrian Era to the Tertiary Epoch of the Cenozoic Era.In Palaeozoic deposits there are many limestone beds, and Mesozoic deposits oftentimes contain limy shales.Groundwater in sedimentary rocks is usually contained in limestones or limy rocks. Groundwater can also be found in igneous rocks and metamorphic rocks which are derived from old sedimentary rocks. Groundwater in the sedimentary rocks is fissure and stratum water, and in igneous rocks and metamorphicrocks only fissure type water exists. Results of the study made by drilling wells in various types of rocks, the following facts are made clear: In consolidated sedimentary rocks largest quantity of groundwater is found and next in quantity comes the groundwater from granite.On the contrary, the groundwater in metamorphic rocks is found in smaller quantity than in any other rocks. With respect to water quality, the groundwater in granite and metamorphic rocks isbetter than the groundwater in sedimentary rocks.The groundwater in dike rocks is also good.Anyway all the groundwater from these rock systems is good for agricultural use and drinking purpose. In the Korea the shallow groudwater is easily affected by the surface water and gets polluted.The deep groundwater on the contrary is not easily influenced by the surface water body and has the advantage of constant temperature. In developing the groundwater to meet the demand for water, unpolluted and with constant temperature, it is necessary to investigate carefully on these points.
Strong acidic water is flowing out from the old-Nishiazuma Mine Field and it is due to water pollution of the Matsukawa river whose water can't be used for irrigation. A disposition method of the strong acidic water was studied by field survey, with some laboratory tests and investigations for the acidification and neutralization of andesite rocks. As the results, PH value of the strong acidic water indicates from 1.4 to 3.4 and it's water flow is less than 0.273 m3/sec at the present condition. However, it will be possible to decrease less than 0.150 m3/sec in it's flow by means of protection of permeation of rain water under the ground surface near the old mine field. The old mine field is located near Ohgasayama Daichi plateau whose geological circumstance consists of tertiary tuff breccia which is covered unconformably by pyroxene andesite. On the part of this plateau, once there was a disposition area for the strong acidic water, the pyroxene andesite have got acidified up to about 50 m in depth under ground, where PH value indicates 4.0-5.0. But, rocks in deeper layer than the above and distant area from acidified area point out 7.0-8.0 in PH value. The result of infiltration test by two test wells in above mentioned area shows that the coefficient of permeability ‘K’ is 10-4-10-6 m/min and it is supposed that the boundary of strata is main water way of groundwater. The result of experiment in laboratory shows that the water changes to PH value 4.3 in the first 12 hours when the strong acidic water of PH value 1.4 touchs fresh rocks in this area and in 6-10 days it, which has been the most promoted in neutralization, become PH value 4.8. The disposition process of the stong acidic water is carried out as follows: 1) a pipeline has been laid between the water's comeout point and the treatment site where a lot of wells are provided; 2) the water in question transferred through a pipeline flours into the wells for permeation without any artificial pressure; 3) the contaminated water injected into the wells is neutralized in the andesite and give off again; 4) it flows into Yazawa river and Matsukawa river. The treatment water has no effect on the river, for it is almost neturalized.