Abstract: A series of pneumatic fracturing model tests are performed using a new developed laboratory apparatus to investigate the effect of air pressure and overburden load on pneumatic fracturing. The results indicate that the injection of high-pressure air into soil induces pneumatic fractures, which accelerate the dissipation rate of excess pore pressure. Before the air injection is stopped, the width of fracture reaches maximum and the fracture closes gradually when the air injection is stopped. The width of residual fracture is about one percent of the maximum width of fracture. The results also show that influence area of pneumatic fracturing and width of fractures are relating with air pressure and overburden load. Air pressure has more significant influence than overburden load. The influence area of pneumatic fracturing is related hyperbolically with air pressure; however, the width of fracture has a positive linear correlation with the air pressure, and has a negative linear correlation with the overburden load.

Key words: pneumatic fracturing, air injection pressure, overburden load, influence area, width of fractures