開口節理の成因とシーティング節理の地理的出現頻度について

概要

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Open joints are paticular concern for engineering geologists, since they deteriorate elasticity and impermiability of rock mass. Their genesis has not been discussed in detail up to the present, presumably due to a limited number of the outcrops. In this study, the open joints are investigated in tunnels at mainly four dam project sites, with regards to topography and geology. The reached conclusions are as follows. 1) Open joints are oriented nearly parallel to the ground surface and exist only at shallow depth, so that they can be regarded as a variety of sheeting joints. 2) Open joints occur in the rock mass when the chemical weathering induces remarkable volume increase, and release of confining pressure at alternating beds causes differential rebound. 3) As far as “Green tuff region” in Japan is concerned, open joints, i.e. sheeting joints are of general occurence. 4) The rock mass with open joints is accompanied by landslide topography, although the rock mass without open joints is not, therefore the open joints are assumed to be prerequisite condition for landslide. 5) Vertical open joint at ridge top is presumably the origin of “ridge top depression”.
社団法人東京地学協会の論文