Eccentric Casing System
  • Eccentric Casing System
  • Eccentric Casing System
  • Eccentric Casing System
  • Eccentric Casing System

Eccentric Casing System

Casing advancement system for overburden drilling

Eccentric casing systems are specialized drilling tools used in complex ground conditions such as gravel layers, colluvial deposits, and running sand formations.

They effectively prevent borehole collapse and buried-bit incidents, ensuring drilling quality and construction efficiency.

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Structure
Structure
  • Pilot bit
  • Reaming
  • Guide Device
  • Casing shoe
  • DTH hammer
  • Steel casing

An eccentric casing drilling system typically consists of a DTH hammer, eccentric casing drilling assembly, casing shoe, and casing. The eccentric drilling assembly is generally composed of a pilot bit, eccentric reaming bit, centralizer, and locking/unlocking mechanism.

Working Principle
  • Working Principle
  • Working Principle

During drilling, the eccentric drilling assembly is lowered through the casing into the casing shoe. When the drill rotates forward, the eccentric bit automatically swings out under bottom-hole friction and creates a borehole larger than the casing’s outer diameter under the DTH hammer’s impact. At the same time, the centralizer shoulder pushes the casing shoe, allowing the casing to advance synchronously with the drilling process to stabilize the borehole.

Once the required depth is reached, the drill string is rotated in reverse by a specific angle, causing the eccentric bit to retract. The drilling assembly can then be withdrawn through the casing.

Advantages of Eccentric Casing Systems

Compared with concentric casing systems, eccentric systems can achieve the same finished borehole diameter using a smaller casing size, reducing material cost while increasing penetration rate and lowering compressor fuel consumption. Concentric systems enter the ground at full diameter, making them more difficult to advance through boulders or hard rock and more prone to casing extraction problems or casing breakage. Eccentric systems avoid these issues, offering a more reliable and efficient solution in challenging ground conditions.

Applications

Eccentric casing systems are widely used in drilling operations across hard, broken, loose, and otherwise complex ground formations. Typical applications include geohazard mitigation, hydropower works, urban high-rise foundation support, and road and railway construction.

Operation Guidelines

Before lowering the assembly, inspect all connections and ensure the eccentric bit can rotate freely. During drilling, monitor casing advancement and cuttings discharge; perform strong air flushing every 0.3-0.4 m of penetration. When drilling is complete or the pilot bit needs replacement, first clean the hole, then reverse rotate at low speed to retract the eccentric bit before lifting the assembly.

Technical Parameters
Model Casing OD, mm Casing min. ID, mm Reaming diameter, mm Casing shoe min. ID, mm Pilot bit max. OD, mm DTH hammer
SPM70A-70-89 89 77 98 71 70 SPM70
SPM90-85-108 108 94 114 86 85 SPM90/90-I
SPM335-85-108 108 94 114 86 85 SPM335
SPM335-90-114 114 101 118 91 90 SPM335
SPM335-100-127 127 114 136 103 100 SPM335
SPM110-120-146 146 130 156 121 120 SPM110/110- I
SPM4.5-120-146 146 130 156 121 120 SPM4.5
SPM340-120-146 146 130 156 121 120 SPM340
SPM350-140-168 168 152 185 142 140 SPM350/SPMS50
SPM350-145-178 178 152 185 146 145 SPM350/SPMS50
SPM350-150-183 183 152 198 152 150 SPM350/SPMS50
SPM360-165-194 194 185 210 166 164 SPM360/S60
SPM360-186-219 219 201 240 187 186 SPM360/S60
SPM380-203-245 245 221 270 206 203 SPM380/S80
SPM300-241-273 273 257 300 242 241 SPM380/S80
SPM380-285-325 325 308 365 286 285 SPM380/S80
SPMS100-285-325 325 308 365 286 285 SPMS100
SPMS100-305-355 355 327 390 307 305 SPMS100
SPMS100-325-377 377 347 400 326 325 SPMS100

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.