Strain Changes Caused by the Change of the Water Level of the Reservoir

Abstract

The relation between ground-strain changes observed with laser extensometers at the Amagase Observatory and the change of the water level of the Amagase Reservoir existing near the observatory has been investigated. As results, when the water level in the reservoir drops from an elevation of 70 m to an elevation of 60 m, the horizontal and vertical components of laser extensometers installed in normal directions to the axis of the tunnel show remarkable changes of ground-strains, i.e. the extension of about 2×10⁷ and contraction of about 1×10^-7, res pectively. Horizontal components along the axis of the tunnel are not so much affected by the change of the water level. In order to explain these observational results, we consider a seepage model of the ground water in the porous medium : According to the sudden change of the water level of the reservoir, only the normal stress in the direction across the tunnel may be produced in the vicinity of the tunnel and then remarkable changes of ground-strains may be observed across the tunnel.