Ring Bit With Pilot Bit - Tube Umbrella Forepoling Drill Bits For Tunnel Pre Support
Our tube umbrella combined drill bit assembly (ring bit matched with pilot bit) is specifically engineered for 89mm forepoling steel pipes, featuring premium tungsten carbide inserts designed for soft stratum tunnel advance support operations.
Product Specifications
| Component |
Specification |
| Outer ring drill diameter |
71mm |
| Tungsten carbide inserts for ring bit |
Two groups of 3*11mm wear resistant carbide tips |
| Net weight of ring bit |
3.4kg |
| Central pilot drill diameter |
100mm |
| Tungsten carbide inserts for pilot bit |
6 pieces of 3*11mm impact resistant carbide blocks |
| Net weight of pilot bit |
2.05kg |
| Matching standard pipe |
89mm tunnel forepoling pipe |
Working Principle
This paired ring and pilot drill set serves as the core fitting of self-drilling forepoling systems, enabling simultaneous borehole drilling and pipe installation. The ring drill component is permanently welded onto the front end of the primary forepoling starter pipe, acting as the casing shoe for pipe penetration. The drill rod fitted with a pilot bit runs through the inner cavity of the forepoling pipe and locks tightly with the ring bit via built-in locking mechanism.
Construction workflow: Lock the drill rod in line with preset drilling angles to start boring. The front pilot drill carves out the central hole and transfers percussive force evenly to the surrounding ring bit. Once drilling reaches target depth, reverse the drill rod to disengage the lock assembly, then pull the drill rod backward out of the bore. The forepoling pipe and welded ring bit stay fixed inside the drilled hole after rod retraction, completing full one-step pipe embedding.
Borehole straightness is critical for both construction quality and total project expenditure. Thanks to the coordinated design of central pilot positioning and peripheral ring reaming, our tube umbrella drill kit delivers ultra-smooth drilling with minimal deviation, guaranteeing perfectly straight boreholes for subsequent grouting and support installation.
Core Performance Advantages
- Precise straight borehole forming: Central pilot positioning eliminates drilling deflection, avoids pipe sticking and secondary rework, improves overall construction precision
- Outstanding cost efficiency: Integrated drilling pipe laying simplifies site procedures, shortens construction periods and lowers labor machinery operating costs
- Exceptional durability: High strength tungsten carbide inserts withstand heavy impact and abrasive strata, extending service life in broken rock, soft clay and mixed loose ground
Application Range
This matched pilot and ring drill kit is universally adopted for tunnel umbrella arch advance support operations in weak unstable strata.
The central pilot bit takes charge of central hole boring and percussive energy transmission, while the integrated ring bit casing shoe unit (welded to starter pipe front) completes circumferential reaming. Linked by a reliable locking system, the two drill parts work synchronously to carve boreholes and push support pipes into soil simultaneously.
It fits multiple engineering scenarios including highway tunnels, railway tunnels, municipal underground passageways, mine laneway excavation and urban underground foundation reinforcement, making it an indispensable drilling tool for safe soft ground tunneling construction.
