Discovery and significance of water-gas pressure pulsation effect within karst cavity

Through the generalization of geological model of collapse, aphysical experimental model was designed to explore the changeof water-gas pressure within the karst cavity under the conditions of both openand closed systemswhen groundwater level declined. The experimental results show that, (1) When the karst cavity is of a closed system, negative pressure with regular fluctuations appears during the declining process of groundwater. Their periodicity and amplitude of fluctuations relate well to the initial water level. (2) Once the airtight systemsuddenly turns into openone, a sudden change of water-gas pressure within karst cavity occurs. This change value could reach 3 times of original value. (3) The periodical high-frequency vibration of water-air pressure is acting on the cavity roof during the declining process of groundwater and has the characteristics of pressure pulsation.(4) The change of water-gas pressure caused by the decrease of water level under closed condition can be described by a linear function of time variable. The slope of the function is affected by the section area of karst cavity and the outlet. The intercept of the function is closely related to initial water level. The effect of high-frequency vibration of water-air pressure on overburden needs further studies,which will contribute to the formation mechanism of karst collapseand breakthroughs in prevention research.