Abstract
The effect of underground water on the borehole volumetric strainmeter is investigated by conducting continuous measurement of the underground water level in the borehole at Yugawara, Kanagawa Pref., central Japan.
The dilatational change soon appears after the rising of the underground water level, but about two days later, the strainmeter begins to show the compressional sense. The former feature may be explained by the effect of underground water that decreases stress in the rock surrounding the strainmeter, which brings about the expansion of volume strain. On the other hand, the latter is explained by the increase of load due to the rising of the underground water level to the rock underneath the water table.
Characteristics of strainmeter response to the change of the underground water level exhibit seasonal variation, which may indicate the change of transfer function due to difference of the underground condition.
