PREDICTION OF COLLAPSE OF UNDERGROUND CAVITY FROM GROUND SURFACE DISPLACEMENT AND ITS COUNTERMEASURE AGAINST INTERNAL EROSION

Abstract

 This research aimed at studying the method to predict cavity collapses from observed ground surface displacement caused by development of the underground cavity. We investigated the relationship between the dimension of a cavity and that of the ground surface displacement by conducting a series of large-scale hydraulic experiments. The amount of the ground surface displacement has been shown to have high correlations with the development of an underground cavity. It was also clarified that the collapse of the cavity tends to occur within the area where the ground surface displacement ensued at the timing when suction around the cavity became lower by rising ground water level. This research further studied systematically the geotechnical filter’s deterrent effect against internal erosion so as to establish the effective countermeasure. As a result, it was verified that the geotechnical filter keeps sufficient deterrent effect under strong hydraulic forces under conditions where the median particle diameter ratio is less than 25 and the uniformity coefficients are larger than 3 for both sand and geotechnical filter.