ROCK BAHAVIOR MEASURED BY MEANS OF BOREHOLE STRAIN GAUGES DURING A LARGE UNDERGROUND CAVERN EXCAVATION

Abstract

The vertical strain measurement in a rock mass was carried out by means of borehole strain gauges during progressive excavations of an underground powerhouse cavern, measuring 24m wide, 46.6m high and 134.5m long at 280m below the ground surface. Through the measurement, the following phenomena have been clarified, such as the irregular distribution of the compressive strain, the behavior of the strain increment at the loosened region, the effect of geological structure including discontinuities, and the effect of support system.