Concentric Casing System
  • Concentric Casing System
  • Concentric Casing System

Concentric Casing System

Casing advancement system for overburden drilling

DTH drilling tools used together with concentric casing systems enable an integrated drilling mode in which drilling and casing advancement occur simultaneously. The concentric casing system can drill at any angle, including horizontally, to depths over 100 m.

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As a highly efficient drilling assembly, the system consists of the following components:

Concentric Casing System
  • Pilot bit
    (featuring large internal flushing ports and front-facing discharge grooves)
  • Ring bit
    (with an internal locking profile that connects to the pilot bit)
  • Casing shoe
    (used to connect the pilot bit to the casing)
  • Casing
Concentric Casing System

The casing shoe is welded to the casing, while the pilot bit and ring bit are locked together using a bayonet-type coupler, which uses matching slots and lugs that twist together to lock the pilot bit and ring bit securely in place. Driven by the DTH hammer, the locked pilot bit and ring bit rotate together to drill a hole sized for the casing. During drilling, the casing shoe and casing remain stationary and do not rotate with the bit. Once the target depth is reached, a slight reverse rotation unlocks the coupling, allowing the pilot bit, hammer, and drill string to be retrieved through the casing. The ring bit and casing shoe normally remain in the hole for casing support, but with special designs they can also be retrieved using the same method.

Advantages of Concentric Casing Systems
  • Simple structure:
    The concentric bit has no complex eccentric opening or closing mechanisms, with fewer components, lower failure rates, and easier maintenance.
  • High stability:
    The bit maintains reliable concentricity with the casing, reducing deviation during drilling and making it suitable for applications requiring strict verticality, such as foundation piles and anchor holes.
Applications

Concentric casing systems are suitable for relatively stable formations without hard interlayers or large boulders. Typical uses include:

  • Drilling cast-in-place piles in foundation construction
  • Excavation support in soft soils (e.g., soil nail walls, anchor holes)
  • Creating cutoff walls in hydraulic engineering
  • Core drilling in geological exploration where an intact borehole wall is required
Technical Parameters
Model Casing OD, mm Casing min. ID, mm Max. wall thickness, mm Reaming diameter, mm Compatible DTH hammer Max. bit pass-through diameter, mm
SPMTX35A-85-114 114 101 7 120 SPM35A 85
SPMTX35A-95-127 127 108 9 135 SPM35A 95
SPMTX45A-115-146 146 126 10 152 SPM45A 115
SPMTX55A-140-168 168 148 10 171 SPM55A 140
SPMTX55A-145-178 178 158 10 185 SPM55A 145
SPMTX55A-152-183 183 163 10 191 SPM55A 152
SPMTX65A-165-194 194 174 10 206 SPM65A 165
SPMTX65A-185-219 219 199 10 235 SPM65A 185
SPMTZ65A-205-245 245 232 6.5 258 SPM85A 205
SPMTX85A-220-273 273 249 12 285 SPM85A 220
SPMTXS100-265-305 305 281 12 325 SPMS100 265
SPMTXS100-279-323 323 299 12 345 SPMS100 279
SPMTX112A-311-355 355 331 12 375 SPM112A 311
SPMTX112A-350-406 406 381 12.7 428 SPM112A 350
SPMTX112A-391-457 457 432 12.7 480 SPM112A 391
SPMTX112A-420-508 508 476 16 520 SPM112A 420

The rock drilling tools are compatible with handheld rock drills, drilling jumbos, surface rock drills, and rock drill and splitter commonly used in international engineering machinery.

Mining applications require high wear resistance and fracture toughness. Durable alloy spherical-button bits are commonly used, suitable for drilling hard rock and medium to large-diameter blast holes.

Tunnel drilling typically uses cross bits or small spherical-button bits paired with lightweight rock drills to improve maneuverability and excavation efficiency.

Surface mining blast-hole drilling commonly uses large-diameter spherical-button bits and extended threaded rods, paired with medium- or heavy-duty rock drills to ensure hole diameter and depth.

Small blasting operations typically use multi-sided rods and flat-edge ballistic button bits, suitable for handheld rock drills to quickly create shallow holes.