Abstract
A collapse of a tunnel face by seepage water often occurs in sandy ground. In previous studies, a resistance of sandy ground against seepage water was studied in view of soil mechanics. In addition, it was conceivable that the resistance of sandy ground against the seepage water was influenced by geological conditions. However, the influence of geological conditions was not studied. Therefore to understand geologic factors on the resistance of sandy ground against the seepage water, we examined soil physical properties and observed facies and microscopic structure of undisturbed sandy samples obtained from Pleistocene sand layers. The resistance of the sandy ground against the seepage water had good correlation with the clay content, the coefficient of uniformity and the cohesion. As a result of examining geological factors concerning to these physical properties, it became clear that the coefficient uniformity was related with sedimentary environment. Moreover the cohesion was different by the amount of clay minerals and cement materials covering up sand fabrics, and it was affected by the diagenesis. We concluded that sedimentary environment and diagenesis influenced the resistance of the sandy ground against the seepage water.
