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Abstract A series of model tests are developed to investigate the effect of pneumatic fracturing with or without vacuum pressure. The model test results indicate that pneumatic fractures are concentrated on jet in horizontal direction，and the dissipation of excess pore pressure is divided into fast dissipation stage and slow dissipation stage. The results also show that the number of fractures is decreased with vacuum pressure. The maximum excess pore pressure is increased with air injection pressure，and decreased with vacuum pressure. The fast dissipation stage lasts for 20–30 minutes and dissipation pressure is about 70% of maximum excess pore pressure. The dissipation rate is increased with vacuum pressure. According to the test results，the instantaneous and low- pressure pulse is suggested in the process of vacuum preloading.
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Received: 13 August 2013
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2014, Vol. 33 
