Difficult formations such as gravel, boulders and even stiff clay and sand, require specialized drilling techniques. HANJIN DRILLING utilizes a very cost-effective drilling method called Down-Hole Casing Advance (OVERBURDEN SYSTEM). This technology allows drilling and casing of the borehole to occur at the same time even while going through varying lithologies.
OVERBURDEN SYSTEM utilizes an eccentric reamer bit to drill a hole large enough for casing to advance behind it. As the bit on the hammer rotates, the reamer swings out around the eccentric shaft of the bit. The reamer enlarges the hole and allows the casing to be advanced while you drill. The drill cuttings are removed from inside the casing by the airflow that is created at the surface which is used to drive the down hole hammer. Once in bedrock, the drill string is rotated in the opposite direction causing the bit to "fold-in" allowing it to be pulled from the casing. A standard bit is then used to drill into bedrock.
This drilling technology can be used with standard air rotary drill rigs and also in with hollow stem auger equipment. An auger can be used while drilling through unconsolidated formations and when refusal is met, the rig can be retrofitted with a down-hole hammer and casing to drill through more difficult formations. This eliminates the need to mobilize a larger, more costly rig to complete the boring or well.
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