Abstract
The relationship between the ground strain change and the water level variation in the bore-hole of the volumetric strain meter is investigated. At Shizuoka, the strain appears in the dilatational sense with rise of water level, whereas at Aziro, uplift of the groundwater table results in contraction.
The latter sense of correlation can be attributed to the increase of groundwater loading on the local rocks. On the other hand, the correlation as observed at Shizuoka is explained by the increase of pore pressure due to rising of groundwater level, which decreases stress in the rock surrounding the strainmeter and causes volumetric strain expansion.
The theoretical correction of the observed strain for variation of the underground water table is difficult, because the water level in the bore-hole does not necessarily represent the water table which controls the local stress affecting the strainmeter.
