Construction Technology of Self-drilling Long Rock Bolts with Jumbo Drill Rig
Abstract
In tunnel excavation, underground mining and underground engineering construction, surrounding rock support is the core procedure to ensure construction safety and structural stability. For broken, weakly cemented and soft fractured rock strata, conventional rock bolt construction faces prominent problems such as hole collapse, difficult bolt penetration and low anchoring efficiency. To solve the above construction pain points, this paper introduces the construction technology of self-drilling long rock bolts matched with jumbo drill rigs. This technology integrates drilling, bolt feeding and grouting into one continuous process, omitting traditional procedures including hole cleaning and separate bolt installation. Combined with the full-automatic positioning and high-precision drilling advantages of hydraulic jumbo drill rigs, it realizes mechanized, high-efficiency and high-quality anchoring construction. This paper elaborates the working principle, construction preparation, detailed construction process, key quality control points, construction advantages and engineering application effects of this technology, providing reliable technical references for similar underground surrounding rock support projects.
1. Introduction
With the rapid development of infrastructure construction and underground mineral resource exploitation, tunnel engineering and deep mining projects are gradually expanding to deep and complex geological areas. Surrounding rock conditions become more complex, featuring frequent fractured zones, loose rock mass and high groundwater seepage. Traditional separate drilling and anchoring construction easily causes hole wall collapse after hole forming, which makes it impossible to place long rock bolts in place, seriously restricting construction progress and threatening underground operation safety.
A self-drilling long rock bolt is a hollow integrated anchoring component integrating drill bit, hollow bolt rod and connecting sleeve. It cancels the procedure of pulling out the drill rod after hole forming, and completes drilling and anchoring synchronously. The full hydraulic jumbo drill rig, as a mature underground mechanized construction equipment, has accurate positioning, powerful rotary-percussive drilling capacity and multi-station simultaneous operation functions. The matching application of jumbo drill rigs and self-drilling long rock bolts perfectly adapts to complex weak surrounding rock working conditions. Compared with manual and semi-mechanized anchoring methods, this technology greatly reduces manual operation risks, shortens construction period and improves overall support safety. Therefore, it has been widely promoted in modern tunnel and underground mine support projects.
2. Overview of Core Equipment and Working Principle
2.1 Introduction to Core Construction Equipment
2.1.1 Jumbo Drill Rig
The hydraulic jumbo drill rig adopted in this construction is specially designed for underground narrow working spaces. It is equipped with flexible hydraulic drilling arms, high-power rotary-percussive drilling systems and automatic positioning systems. The equipment can realize horizontal, vertical and arbitrary angle drilling according to surrounding rock design requirements. Meanwhile, it supports long-distance continuous drilling, which meets the construction demands of long rock bolts with a single length ranging from 6m to 12m. Its automatic feeding function avoids manual bolt transportation and installation, reducing personnel exposure in high-risk surrounding rock areas.
2.1.2 Self-drilling Long Rock Bolt
The self-drilling long rock bolt consists of an alloy drill bit, full-thread hollow anchor rod, connecting sleeve, stop-grouting plug, backing plate and nut. The hollow inner cavity of the bolt rod serves as a grouting channel. During construction, cement mortar can be directly injected into rock fractures through the bolt inner cavity to realize integrated drilling and grouting. For ultra-long anchoring requirements, multiple sections of bolt rods can be connected via standard connecting sleeves to meet customized anchoring depth demands without secondary hole expansion.
2.2 Basic Working Principle
The drill arm of the jumbo drill rig is accurately positioned to the designed anchoring hole site. The drilling head is connected with the tail of the self-drilling rock bolt, and the drill bit at the front end of the bolt directly impacts and cuts the rock mass. The bolt rod advances forward synchronously with drilling, replacing the traditional drill rod. After reaching the designed anchoring depth, high-pressure grouting is carried out through the hollow channel of the bolt rod without withdrawing the bolt. Cement slurry fills the gaps between the bolt rod and hole wall as well as internal rock fractures. After the slurry solidifies, the bolt, grout and surrounding rock form an integral bearing structure, which effectively restrains surrounding rock displacement and prevents rock mass loosening and collapse.
3. Complete Construction Process
3.1 Pre-construction Preparation
Geological survey and scheme optimization: Detect on-site surrounding rock grade, fracture development degree and groundwater distribution, and confirm bolt diameter, length, spacing and grouting pressure parameters. Formulate targeted construction schemes for water-rich fractured strata.
Equipment inspection and commissioning: Check the hydraulic system, drilling impact power and positioning accuracy of the jumbo drill rig; test the tightness of the grouting pump and pipeline to avoid slurry leakage during construction. Inspect the appearance and thread integrity of self-drilling bolts to ensure no damage during installation.
On-site safety clearance: Remove loose dangerous rocks on the tunnel face and side walls in advance, set up safety warning areas, and guarantee safe walking and operating space for the drill rig.
3.2 Accurate Positioning of Drill Rig
Drive the jumbo drill rig to the designated construction position, adjust the support legs to fix the equipment stably. Operate the hydraulic drill arm to align the drilling center with the preset anchoring hole position strictly according to the design angle and depth. The positioning error is controlled within ±20mm to ensure the anchoring effect meets design requirements.
3.3 Integrated Drilling and Bolt Feeding
Start the rotary-percussive drilling system of the drill rig. The front alloy drill bit cuts the rock mass, and the hollow bolt rod advances continuously. Compressed air is delivered through the inner cavity of the bolt to discharge rock slag out of the hole in real time. For long bolts exceeding the single-section length, stop drilling after reaching the limit length of a single rod, connect the next section of bolt via a connecting sleeve, and continue drilling until reaching the designed depth. This process eliminates hole cleaning and secondary hole repair procedures required in traditional construction.
3.4 High-pressure Grouting Operation
After drilling is completed in place, keep the bolt fixed inside the hole without pulling out. Connect the grouting pipeline to the bolt tail, install a stop-grouting plug at the hole opening to prevent slurry backflow. Adopt graded cement mortar with a reasonable water-cement ratio for continuous high-pressure grouting. Grouting pressure is controlled at 2.0MPa to 3.5MPa according to surrounding rock fracture conditions. Stop grouting immediately when dense slurry flows out stably from the hole opening.
3.5 Installation of Accessories and Maintenance
After grouting is finished, install the backing plate and nut quickly before the initial setting of cement slurry, and apply appropriate pre-tightening force to make the backing plate closely fit the rock wall. Conduct natural curing for 24 to 48 hours. No excavation or blasting operation shall be carried out near the anchoring area during the curing period to ensure the grout reaches designed bonding strength.
4. Key Quality and Safety Control Measures
4.1 Construction Quality Control
Strictly control drilling angle and depth deviation to avoid irregular bolt arrangement affecting overall supporting force.
Match grouting pressure and water-cement ratio according to actual groundwater conditions; increase grouting pressure appropriately for water-rich fractured strata to ensure full filling of fractures.
Check the connection tightness of bolt sleeves one by one to avoid bolt separation under impact load after construction.
Conduct regular drawing tests on finished rock bolts to verify anchoring bearing capacity meets design standards.
4.2 On-site Safety Control
All operators must receive professional training on jumbo drill rig operation and underground construction safety before taking posts.
Stop drilling immediately if abnormal rock burst or severe slag spraying occurs during construction, and resume operation after eliminating hidden dangers.
Keep ventilation systems running continuously during underground construction to ensure qualified air quality in the working face.
5. Technical Advantages Compared with Traditional Construction Technology
Comparison Items | Traditional Separate Drilling and Anchoring Technology | Jumbo Drill Rig + Self-drilling Long Rock Bolt Technology |
|---|---|---|
Anti-hole-collapse Capacity | Poor, easy hole collapse in broken rock | Excellent, no need to pull out drill rod, avoid hole collapse fundamentally |
Working Procedures | Multiple procedures: drilling, rod pulling, hole cleaning, bolt feeding, grouting | Integrated process, simplified working steps |
Manual Demand | Large manual participation, high operation risk | High mechanization, few on-site workers |
Construction Efficiency | Low, long single-hole construction time | Improved by more than 40%, shortened overall construction period |
Anchoring Integrity | Easy to have cavity inside the hole, poor bonding effect | Full-hole grouting, tight combination of bolt and rock mass |
Comparative Analysis on Application Effects Between Three-arm Drill Jumbo and Hand-held Rock Drills in Tunnel Construction
Abstract
Drilling operation is one of the most critical working procedures in tunnel excavation and underground engineering construction, which directly determines the construction progress, surrounding rock support quality, personnel safety and overall project cost. At present, hand-held rock drills and three-arm full-hydraulic drill jumbos are two mainstream drilling construction equipment widely used in domestic and overseas tunnel projects. Hand-held rock drills feature low procurement cost and flexible operation, while three-arm drill jumbos represent mechanized and intelligent construction equipment for modern tunnels. This paper systematically compares the two types of equipment from five core dimensions including construction efficiency, construction safety, hole-forming quality, comprehensive construction cost and applicable working conditions based on actual tunnel engineering cases. The research results verify that three-arm drill jumbos have overwhelming advantages in large-section, long-distance and high-risk tunnel construction. Meanwhile, this paper clarifies the reasonable application scenarios of the two devices, providing scientific references for equipment selection and construction scheme optimization of tunnel engineering projects.
Keywords: three-arm drill jumbo; hand-held rock drill; tunnel construction; construction efficiency; construction safety; mechanized construction
1. Introduction
With the rapid advancement of railway, highway and municipal tunnel infrastructure, tunnel construction is gradually developing towards large cross-section, deep burial and complex geological conditions. Traditional manual drilling construction relying on hand-held rock drills can no longer meet the requirements of modern tunnel projects for high efficiency, high safety and standardized construction. The three-arm full-hydraulic drill jumbo, as core intelligent tunnel construction equipment, integrates automatic positioning, multi-station simultaneous drilling, hydraulic power drive and precise angle adjustment functions. It has been widely popularized in large-scale tunnel projects in recent years.
Nevertheless, many small and medium-sized tunnel projects still adopt hand-held rock drills due to limited project budget, narrow construction space and short construction cycle. In order to select matching drilling equipment more reasonably according to actual project conditions, this paper carries out an in-depth comparative study on the practical application effects of the two drilling devices in tunnel sites, analyzes their respective strengths, defects and suitable scenarios, so as to help construction units reduce construction risks and improve overall engineering benefits.
2. Overview of Two Kinds of Drilling Equipment
2.1 Hand-held Rock Drill
The hand-held rock drill is a small pneumatic or hydraulic drilling tool driven by compressed air. It is light in weight, easy to carry and operate, with low purchase cost and no requirement for large walking space. Usually, construction workers hold the equipment manually to complete blasthole drilling and anchor hole drilling. Its disadvantages are obvious: high manual dependence, strong vibration during operation, serious dust pollution, limited drilling depth and low drilling accuracy. It belongs to typical semi-mechanized construction equipment and is mostly used for small-section tunnels, local repair drilling and short-distance tunnel projects.
2.2 Three-arm Drill Jumbo
The three-arm drill jumbo is a special full-hydraulic mobile drilling platform designed for underground tunnel working conditions. It is equipped with three independent hydraulic drilling booms, which can realize simultaneous drilling operation at three different positions. The equipment supports automatic hole position positioning, fixed-depth drilling and automatic rod changing. The whole drilling process realizes unmanned operation in the working face, and construction personnel only need to operate equipment outside the dangerous area. It is suitable for large-section highway tunnels, railway tunnels and mine roadway excavation projects with high requirements for construction progress and safety.
3. Detailed Comparison of Application Effects in Tunnel Construction
3.1 Construction Efficiency Comparison
In terms of single-hole drilling speed, the gap between the two devices is small under shallow drilling conditions. However, considering overall working efficiency including hole layout, position adjustment and multi-hole construction, the three-arm drill jumbo has far better performance.
In actual tunnel working face construction, one three-arm drill jumbo can complete 90 to 120 blast holes within 3 hours for a standard tunnel excavation cycle. In contrast, to finish the same quantity of drilling work, at least 8 sets of hand-held rock drills and corresponding construction workers are required, and the whole working period takes more than 5 hours. Besides, the three-arm drill jumbo realizes integrated operation of walking, positioning and drilling, saving a lot of time for manual position adjustment. Continuous operation data shows that the overall construction efficiency of three-arm drill jumbo is improved by more than 55% compared with traditional hand-held rock drills.
3.2 Construction Safety Performance Comparison
Construction safety is the biggest advantage of three-arm drill jumbos. When using hand-held rock drills, operators need to stand directly below the tunnel working face for long-time manual operation. They are exposed to multiple safety hazards including falling loose rocks, tunnel collapse risks, high-frequency vibration injury and high-concentration dust. Long-term operation will also cause occupational diseases such as vibration-induced white finger and pneumoconiosis for workers.
For three-arm drill jumbos, all drilling work is completed by mechanical arms automatically. Workers operate the equipment in a safe area far away from the tunnel face, completely avoiding direct contact with dangerous working areas. Meanwhile, the equipment is equipped with automatic dust removal devices and safety protection support legs, which can effectively prevent rock fall accidents. Statistical data from tunnel construction sites show that the safety accident rate of drilling procedures using three-arm drill jumbos is close to zero, while manual hand-held drilling accounts for more than 60% of minor safety accidents in tunnel sites.
3.3 Hole-forming Quality Comparison
Hole-forming accuracy directly affects blasting effect and subsequent surrounding rock support quality. Restricted by manual operation errors, hand-held rock drills are difficult to control drilling angle and drilling depth stably. The deviation of blast hole angle is usually greater than 3°, and inconsistent hole depth often leads to over-excavation or under-excavation of tunnel sections, increasing subsequent concrete backfill cost.
The three-arm drill jumbo adopts laser automatic positioning system, with drilling angle deviation controlled within ±0.5° and accurate fixed-depth drilling. Uniform blast holes ensure smooth tunnel excavation outline, reduce tunnel over-break rate by more than 80%, and greatly save backfill concrete materials and construction time. In anchor bolt construction matching self-drilling rock bolts, high-precision holes also significantly improve overall surrounding rock supporting effect.
3.4 Comprehensive Construction Cost Comparison
Hand-held rock drills have low initial procurement cost and simple maintenance, so the early investment is low. But it requires a large number of on-site workers, resulting in high labor costs. In addition, poor hole-forming quality leads to extra consumption of explosives, drilling rods and concrete backfill materials, bringing higher invisible construction costs.
Although the three-arm drill jumbo has high equipment purchase and maintenance costs in the early stage, it greatly reduces labor input, material waste and accident compensation costs in the whole construction cycle. For long-cycle and large-section tunnel projects, the comprehensive construction cost can be reduced by about 18% compared with manual drilling. Only for ultra-short and small tunnel projects, hand-held rock drills have slight cost advantages.
3.5 Applicable Working Condition Comparison
Evaluation Item | Three-arm Drill Jumbo | Hand-held Rock Drill |
|---|---|---|
Tunnel Cross-section | Medium and large cross-section tunnels | Small cross-section, narrow roadway |
Construction Cycle | Long-term, continuous excavation | Short-term, partial remedial work |
Geological Condition | Hard rock, fractured surrounding rock | Soft rock, simple geological stratum |
Space Requirement | Large working space required | No strict space limitation |
