| The relation was analyzed between the amount of dust released at the time of machine digging and geological condition from the questionnaire. As a result, the following became clear.(1)With the fractured rock mass in a sedimentary rock, more dust was released from the rock mass of higher unconfined compression strength such as sandstone, slate and shale than those of lower unconfined compression strength such as mudstone.(2) From the viewpoint of the degree of mineral crystallization of a rock, more dust was released at the abyssal rocks with the crystalline structure such as granite, and gabbro than at the igneous rock with the amorphous substance such as rhyolite, andesite, and basalt.(3) Even if rock quality such as crystalline rock is a hard metamorphic rock, the rock mass exfoliates easily because of schistosity development, and the amount of dust comparatively decreases.(4) The dust increases with harder rock mass such as igneous rock (granite and gabbro), and sedimentary rock (sandstone, slate and shale), as part of the massive structure. In other words, more dust is released from the massive rock mass that is prone to brittle fracture with the unconfined compression strength is more than 100MPa. |
