Tilt Measurement of Rock Mass around Underground Oil Caverns

To monitor the stability of the tunnel and the underground oil caverns, a continuous ground tilt observation was carried out using highly precise down-hole tiltmeters. The ground tilt due to earth tides, atmospheric pressure variation, and earthquakes could be measured clearly. These tilt components were separated from raw data, and the resumption to the former position after tilting by short-term events were observed by applying this analysis. It was confirmed that variation of the tendency to secular fluctuation of the ground tilt is possible by down-hole tiltmeters.