Overburden drilling systems are used when soil and subsurface conditions are not considered to be highly stable. These systems use casings as part of the drilling process to ensure that the drilled hole remains stable. The information below shows the number of overburden drilling systems sold by drilling equipment suppliers worldwide. Note that some specifications described in the following content may not be the same as the specifications followed by your agency. Always check with your State agency’s standards and specifications when using these guidelines.