植生からみた岩盤の風化深度判定とその土木地質学的意義

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The authors engaged in trial researches to grasp correctly weathering process through inspection into forest physiogomy in Chichibu mountainous district, from the view point of both forest pedology and plant ecology. They considered that weathering evidences would be represented by the soil cover thickness of grounds. Generally speaking, a tree keeps its habitat in soil cover, the thickness of which is determined by land shapes, parent rocks and the duration term of weathering process etc. Accordingly it is not so difficult to estimate soil cover thickness by the prevailing species of trees in a district, if the root length of a tree correlates to soil cover thickness. Pinus densiflora, for instance, grows up on sterile lands, such as summits, ridges and steep slopes of mountains, or barren grounds in the relics of landslides and slope failures, because it sustains a thinner soil cover and need more sufficient insolation, while Criptomeria japonica and Chamaecyparis obutusa require a wellfed soil, sufficient water supply and suitable drainage condition, therefore they grow up often on a mountain foot and a tablus slope, where weathering process into such a deeper layer as the afforestation of both kind of the trees is possible. Quercus serrata, Acer Mono and Prunus jamasakura luxuriate in an intermediate zone between the above-mentioned two extreme plant communities, bacuase soil developes to an average grade in this plant zone which occupies an extensive area as a natural forest, consisting of deciduous and latifoliate trees. The authours could estimate approximately the thickness of soil cover of places, where each kind of the foregoing plant community was found, because they witnessed the fact that the penetrating depth of a main root corresponds to 1/5-1/7 of a trunk height. In order to prove the above-mentioned fiied observation, the authors undertook several field experiments, such as test pits, boring works and seismic prospectings on the 37 locations in Chichibu mountainous district, arriving at such conclusion that the thickness of soil cover (=y) interrelates to the ratio of σ/Vp(=x) as an exponential function, that is, [numerical formula] The constants have been determined through calculation by the method of least square, as follows: y=1.758×10^<-0.00817x>…(2) <<thickness of weathering earth>>y=7.007×10^<-0.0626x>…(3) <<depth down to the fresh rock base>>Finally the authors have reviewed the utility of the formula and the graph-3, in regard to application to engineering geology.
一般社団法人日本応用地質学会の論文
1975-03-30

植生からみた岩盤の風化深度判定とその土木地質学的意義

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