航空写真による軟弱地盤の判読〈第1報〉

―微地形の系統的おび計測的分析による判読法の適用について― (1)

抄録

The term soft ground is used to describe areas which are composed mainly of unconsolidated muddy deposits and organic materials, and are found in recent alluvial lowlands. Such areas are causing much trouble during the construction of buildings and civil engineering structures. Ground subsidence due to the taking up ground water, and damage to structures are frequent in such areas.
The basic concepts and techniques used to interpret engineering soils bythesy stematic and morphometric analysis of micro-geomorphology of recent alluvial lowlands using aerial photographs, and their applicability to engineering soil surveys, above all in soft ground conditions, are discussed in this paper.
(I) Basic concepts, problems and techniques of interpretation
1) The methods and techniques of micro-geomorphological analysis are a most important part of interpretation proces singeological, soil and other land surveys by aerial photographs. But we are not satisfied to know the types of landforms alone. In order to interpretsurface materials or soils, geology, it is necessary to establish the system that we can infer these land conditions from the analysis of micro-geomorphology.
In the regions which have boen intensively utilized such as alluvial lowlands of Japan, it is better to interpret surface materials or soils by the analysis of micro-geomorphol ogical features than by the analysis of photographic tone and density. The latter should be analyzed in connexion with micro-geomorphological features of lowlands.
2) The first step to interpre tengineering soils is delimitation of the “micro-landform units” which should be closely related with the physical properties of the soil parent materials. In order to delimitate the “micro-landform units”, the principles and techniques of“ landform type” analysis on aerial photographs which have been developed and systematized by Nakano (1955, 1962^a) and his collaborators (1964) can be applied. These unies are better suited for mapping the surface distribution ranges of soft ground.
The“micro-landform units” which are classified on photographs, and are thought to be the basic terrain units to infer engineering soils, their photographic chracteristics and their relationship to surface materials or parent material of soils are arranged in Table 1-2.
The second step is to group these units into the “landform areas” depending upon the distribution pattern of these units, the geomorphological agents, their topographic locations and other criteria. “Landform areas”grouped by these criteria are one of the terrain units used to examine the geomorphological development or the sedimentary environment over the area during recent years. Considering these factors, the types of soft ground and their occurrence in a“ landform area” can be roughly interpreted using aerial photographs.
“Landformm areas” which can be expected in alluvial lowlands of Japan, main “microlandform units” which are distributed in each“landform area”, and relationship to the occurrence of soft ground are shown in Table 1-3. Fig. 1-1is a chart showing the procedure for engineering soil surveys and soft ground investigations during the preliminary or reconnaissance stage. Detailed relationship between landforms and the distribution of soft ground is tabulated in Table 1-4. (to be continued next number)