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Flexible excavation scheme for single-arm and double-curve-arm rock drilling rigs at tunnel intersections
Release time:
2026-09-21
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Summary:
In tunnel construction, the in‑tunnel junctions—where cross passages, adits, and inclined shafts connect to the main tunnel—feature highly variable spaces and frequent abrupt changes in cross‑section. Traditional hand‑held pneumatic rock drills are poorly suited to these conditions, resulting in significant drilling‑pattern deviations and slow workflow transitions. The introduction of rock‑drilling rigs hinges on precise control of excavation parameters and well‑organized operational sequences, enabling mechanized equipment to effectively address complex cross‑sections. Single‑arm rigs excel in maneuverability, allowing flexible reorientation at branch points and rapid withdrawal; dual‑arm rigs, with their innovative boom design, offer superior adaptability for step‑excavation methods and the construction of tunnels with irregular profiles. When used in combination, these two types can form a coordinated working system.
I. Technical Challenges in Intersection Construction and Corresponding Mitigation Strategies
During construction of the No. 3 adit at the Yue Longmen Tunnel on the Cheng–Lan Railway, where the auxiliary tunnel transitions into the main line at a crossing, the unique “day”‑shaped intersection cluster—shaped by the track structure—posed significant challenges. Leveraging the advantages of mechanized equipment such as rock‑drilling rigs and wet‑spraying robotic arms, and by optimizing the excavation sequence and the initial support system at the crossing, a novel “rapid” construction technique was developed. Compared with conventional methods like “slope climbing” or “pilot tunnels,” this approach shortens the construction schedule and delivers improved economic benefits. This case demonstrates that the key to crossing‑section construction lies in the seamless coordination of work steps: the higher the drilling and blasting accuracy of the rig and the more agile the vehicle‑turning maneuvers, the more promptly the support can be installed.
II. Adaptability of the Hyperbolic-Arm Boom Structure to Irregular Cross-Sectional Configurations at Intersections
Traditional rock‑drilling rigs used in tunnel cross‑section construction are primarily constrained by their straight‑arm design, requiring frequent relocation of the rig and adjustments to blast‑hole orientation when transitioning between upper and lower headings. By contrast, the double‑curved‑arm rig incorporates two articulated joints along its boom, enabling operations below the horizontal plane and accommodating drilling in both upper, middle, and lower headings—thus effectively addressing the limitations of conventional equipment in fully supporting bench‑method excavation. In areas where the cross‑section transitions between different shapes, the double‑curved‑arm configuration can adapt to multiple profile types, facilitating invert excavation and overcoming the inability of traditional rigs to perform invert‑only operations. Moreover, this rig offers an extensive working envelope, with a maximum reach exceeding 16 meters, allowing it to conform to the complex geometry of tunnel intersections and to drill simultaneously in multiple directions—such as the crown, side walls, and invert—thereby achieving three‑dimensional, intersecting drilling.
Compared with double‑arm rigs, single‑arm platforms offer greater flexibility in scheduling during intersection construction. Some single‑arm platforms feature rubber‑tired undercarriages, enabling rapid relocation when used in non‑metallic mining applications and enhancing their maneuverability in narrow intersections. The DJ2E intelligent dual‑arm rock‑drilling rig boasts a compact footprint and highly agile steering; it can operate in minimum cross‑sections of 4.5 m × 4.5 m and is suitable for intersection‑level construction tasks such as cross passages, pilot tunnels, and inclined shafts in medium‑size road and railway tunnels.
III. Improved Accessibility of the Inverted Arch Section and Lower Bench
In intersection tunneling, excavating the invert and drilling the lower bench are areas that traditional equipment struggles to reach. The dual‑curvature boom was designed to extend below the horizontal plane, thereby overcoming the limitation of conventional rock‑drilling rigs in working on the invert. In three‑bench excavation at intersections, the dual‑curvature boom rig first completes drilling in the upper and middle benches, then repositions to drill the lower bench, addressing the challenge of conventional rigs being unable to tackle the lower bench. This single machine can perform full‑section drilling, from the crown down to the invert. This capability makes it particularly well suited to situations involving abrupt changes in cross‑section, where core soil must be preserved, or where layered blasting is required.
In the transition section of intersection structures, the initial support system must be promptly advanced. After completing drilling for excavation holes, the double‑arm boom rig can use its own boom to install system anchor bolts and toe‑anchoring holes, enabling a single machine to perform multiple tasks and reducing equipment‑changeover time. The single‑arm rig also demonstrates excellent suitability for auxiliary anchor bolt installation and advance pipe‑shed operations at intersections, with a drilling depth exceeding 4 meters, thereby meeting the drilling requirements for reinforcing the intersection’s support segment.
IV. Enhancement of Throughflow in the Narrow Section of Intersections through Sliding-Arm Design
At the junction where branch tunnels connect to the main tunnel, the cross‑sectional width is limited and turning radii are constrained, so the equipment’s maneuverability directly affects site‑transition efficiency. The dual‑sliding‑arm computer‑controlled rock‑drilling rig features a pioneering sliding‑arm boom design that significantly reduces the machine’s overall length, enabling it to accommodate various cross‑section types and navigate tight curves—such as those found in inclined shafts, transverse drifts, and pilot tunnels. Coupled with a double‑layer advancing beam, this sliding‑arm configuration overcomes the limitation of conventional drilling rigs, which struggle to adapt to diverse cross‑sections when using different excavation methods. The shorter machine length also allows for in‑place U‑turns within the intersection, facilitating rapid workstation repositioning via rail‑ or trackless transport systems and helping to establish a compact construction rhythm of “driving–supporting–excavating.”
V. Optimization of Construction Organization and Practical Experience in Rapid Intersection Construction
In intersection‑group tunneling, optimizing the excavation sequence at each intersection enables seamless integration of operations such as excavation, support installation, and initial shotcrete application, thereby significantly reducing the cycle time. The key to rapid intersection construction lies in first using a rock‑drilling rig to perform centralized drilling, followed by a single simultaneous blast, while concurrently carrying out muck removal and initial support. This approach eliminates the labor‑intensive delays inherent in conventional methods, where small cross‑sections require repeated entries and exits and frequent dismantling and reassembly of support frames.
Based on experience with blast‑hole drilling using rock‑drilling rigs, once the equipment is in position, the hole‑layout coordinates should first be precisely projected onto the rock face using a laser positioning system. Drilling should then commence from the bottom‑plate holes, with support personnel promptly removing debris and marking the locations of blast holes. When multiple rigs operate in tandem, single‑arm and double‑curved‑arm rigs can be paired: the double‑curved‑arm rig focuses on anchor bolt holes in the upper bench and arch crown, while the single‑arm rig handles auxiliary holes in the lower bench and sidewalls. By appropriately dividing the drilling zones, the overall drilling cycle can be shortened by 20% to 35%.
With the support of advanced geological forecasting, tunneling at intersections should differentiate between weak surrounding rock and hard rock, employing either the bench method or the full-face method accordingly. The double‑arm boom rig exhibits strong adaptability to two‑stage and three‑stage construction in weak surrounding rock, effectively preventing collisions between the boom and the excavation face and enhancing drilling accuracy. In hard‑rock intersection sections, a dual‑rig simultaneous‑drilling approach can further shorten the drilling cycle, enabling seamless integration from excavation to support.
VI. Control of Hole-Placement Accuracy Ensures the Formation of Intersection Profiles
As the intersection represents a stress‑concentration zone in tunnel structures, the smoothness of the excavation profile directly affects the stress state of the support system. Rock‑drilling rigs equipped with laser positioning and automated hole‑layout systems require hole‑position deviations no greater than 3 cm, borehole parallelism errors below 2°, and blast‑hole bottoms to lie on the same cross‑section with a deviation of no more than 10 cm. Computer‑controlled rock‑drilling rigs employ high‑precision positioning to shape the excavation geometry at intersections, effectively minimizing over‑ or under‑excavation and controlling the geometric dimensions of the transition sections. Remote‑control operation allows operators to monitor drilling conditions from a safe distance and adjust the drilling orientation in real time, thereby meeting the stringent directional accuracy requirements imposed by the complex contour of the intersection.
During intersection construction, peripheral blast holes are evenly spaced along the contour at turning points, with each hole inclined outward by 3° to 5° to create a pre-splitting face, thereby minimizing disturbance to the surrounding rock mass in the intersection zone. High‑quality smooth‑surface blasting can achieve a residual hole mark rate of over 90%, effectively ensuring the structural integrity of the intersection’s support system. To meet these precision requirements, the hyperbolic‑arm rig must feature self‑balancing and angular‑display capabilities, enabling automatic correction of the drilling direction along the curved sections of the intersection.
VII. Recommendations for Equipment Configuration and Selection
When selecting construction equipment for intersection tunneling, the following configuration options can be considered. First is the “dual‑boom main unit plus single‑boom auxiliary” combination: the dual‑boom carriage handles the primary full‑section drilling tasks, while the single‑boom carriage performs supplementary drilling and support‑hole operations in the narrow branch passages of the intersection. This setup offers greater flexibility in step‑method intersection tunneling. Second is the single‑machine sliding‑boom carriage configuration: for conditions where the cross‑section width of a side tunnel is severely constrained, a sliding‑boom design should be prioritized, leveraging its short overall length and small turning radius to carry out drilling within limited spaces.
Overall, the increased range of motion of the drilling boom and the enhanced accuracy of hole placement enable the rock‑drilling rig to perform multiple operations at intersections, including drilling, charging, and anchor‑bolt installation. In large‑scale construction of intersection clusters, by carefully planning the excavation sequence and optimizing the rig’s operational workflow, tunneling efficiency can be significantly improved, providing a practical benchmark for mechanized tunnel construction.
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