Blast fracturing usually is used to enhance formation permeability.

Photo courtesy of the Geological and Mining Engineering and Sciences Department of Michigan Technological University.

Blast fracturing is performed by placing high explosives in open bedrock boreholes and then detonating the explosives to create subsurface fractures. Standard drill and blast practice is used, including delayed firing and linear blasthole alignments (typically single- or double-line). Blastholes are drilled through the soil overburden and into the underlying bedrock. Blasthole spacing depends on the particular formation being treated, but typically ranges from three feet to five feet. Relatively large rock volumes are fractured during a single detonation. Water gel explosives typically are used since they are water-resistant.

Blast fracturing is used principally to enhance the permeability of the geologic formations. The technology is applied by creating a blasted-bedrock zone or a blasted-bedrock trench of fractured rock that is positioned transverse to movement of a contaminant plume. Either linear or radial configurations are used depending on site requirements. Plume capture, control and treatment is accomplished by installing pumping wells within the trench. Following creation of the fractured zone, liquid supplements can be introduced to further enhance remediation. Emplacement of granular supplements such as iron powder into blast-fractured zones currently is under study.

Blast fracturing relies on self-propping of the geologic formation in a manner similar to many pneumatic fracturing applications. The basis for self-propping is the Cubic Law, which demonstrates that fluid-flows through open fractures can be substantial.

For site remediation, all reported cases of blast fracturing have been applied to bedrock formations, especially hard rock such as crystalline granite and gneiss and competent sandstone and dolomite. Blast fracturing has most commonly been applied in the saturated zone, although vadose zone and perched zones also can be treated.