reach up to 30 m below ground level. Further, various orientation of the created
fractures may be expected depending on the depth. In the case of the usual depth
(ca 30 m below ground level), subhorizontal crack orientation may be expected
(as described above).
• Plasticity: In highly plastic and cohesive materials with a high proportion of
clayey minerals, plastic deformations of the geological material may take place
during the fracturing. The likelihood that a fracture will form due to cracking of
the geological material is reduced. Plasticity of the material is connected with the
amount and type of the present clayey minerals (an increased plasticity is shown
by unconsolidated geological materials with clayey mineral content >30%).
Plastic materials change volume with a change of water content. Generally,
plastic geological materials with a low water content behave better during the
fracturing than geological materials with a high water content. In plastic geological materials, there is greater likelihood that the created crack would be closed
back so it is recommended that the created cracks are filled with a proppant.
• Secondary structures: They are further important factors influencing the crack
direction and speed of its formation. They particularly include natural layering,
cracks in the rock, foliation areas, and, optionally, the presence of root channels
and/or anthropogenic disturbances of the rock block (old excavations, boreholes,
underground lines, etc.). Secondary structures in the geological bedrock may
behave as preferential ways. They may play a dominant role in spreading pressure
changes in the material, and they usually reduce the fracturing efficiency. While
planning the locations and depth of the fractured areas, these structures should be
taken into account.
• Groundwater level: The geological environment may be fractured regardless of
the fact whether it is in a saturated or unsaturated zone. Groundwater presence
slightly influences the course of the work and the behavior of the environment
after the fracturing. For example, in the case of pneumatic fracturing, the presence
of water in the geological material increases tightness of the environment
preventing penetration of gases, and, thus, higher reach of the fracturing may
be expected.
32.5 Fracturing Feasibility Risks
During planning and implementing the procedures based on geological environment
fracturing, it is necessary to take into account several important factors that could
influence the further remediation process.
• Risk of contaminant mobilization due to fracturing: Geological environment
fracturing causes an increase in its permeability, and thus also increase in the
environment ability to transport contamination that showed low mobility, or was
out of reach of flowing groundwater, before the fracturing. Increase in permeability of the geological environment as well as simplification of access to the
contaminant are the aims of the described methods. Therefore, it is recommended
32 Tool III: Fracturing for Enhanced Delivery of In Situ. . .
629
fractures may be expected depending on the depth. In the case of the usual depth
(ca 30 m below ground level), subhorizontal crack orientation may be expected
(as described above).
• Plasticity: In highly plastic and cohesive materials with a high proportion of
clayey minerals, plastic deformations of the geological material may take place
during the fracturing. The likelihood that a fracture will form due to cracking of
the geological material is reduced. Plasticity of the material is connected with the
amount and type of the present clayey minerals (an increased plasticity is shown
by unconsolidated geological materials with clayey mineral content >30%).
Plastic materials change volume with a change of water content. Generally,
plastic geological materials with a low water content behave better during the
fracturing than geological materials with a high water content. In plastic geological materials, there is greater likelihood that the created crack would be closed
back so it is recommended that the created cracks are filled with a proppant.
• Secondary structures: They are further important factors influencing the crack
direction and speed of its formation. They particularly include natural layering,
cracks in the rock, foliation areas, and, optionally, the presence of root channels
and/or anthropogenic disturbances of the rock block (old excavations, boreholes,
underground lines, etc.). Secondary structures in the geological bedrock may
behave as preferential ways. They may play a dominant role in spreading pressure
changes in the material, and they usually reduce the fracturing efficiency. While
planning the locations and depth of the fractured areas, these structures should be
taken into account.
• Groundwater level: The geological environment may be fractured regardless of
the fact whether it is in a saturated or unsaturated zone. Groundwater presence
slightly influences the course of the work and the behavior of the environment
after the fracturing. For example, in the case of pneumatic fracturing, the presence
of water in the geological material increases tightness of the environment
preventing penetration of gases, and, thus, higher reach of the fracturing may
be expected.
32.5 Fracturing Feasibility Risks
During planning and implementing the procedures based on geological environment
fracturing, it is necessary to take into account several important factors that could
influence the further remediation process.
• Risk of contaminant mobilization due to fracturing: Geological environment
fracturing causes an increase in its permeability, and thus also increase in the
environment ability to transport contamination that showed low mobility, or was
out of reach of flowing groundwater, before the fracturing. Increase in permeability of the geological environment as well as simplification of access to the
contaminant are the aims of the described methods. Therefore, it is recommended
32 Tool III: Fracturing for Enhanced Delivery of In Situ. . .
629