In engineering construction, rock bolt structure is an essential support and reinforcement measure, which is widely applicable under various geological conditions. The choice of rock bolt structure is not only related to the safety and stability of the project but also directly affects the project cost and construction progress. However, in actual projects, due to the influence of various factors such as geological conditions, project scale, and design requirements, selecting an appropriate rock bolt structure has become an important issue that engineers must face.
Types and characteristics of rock bolt structures
Rock bolt structures have many types according to different classification standards. Common classification methods include anchoring method, stress state, material type, etc. The following is a brief introduction to several common rock bolt structure types and their characteristics:
Prestressed anchor
Prestressed anchors are mainly composed of free sections and anchoring sections. The free section refers to the part that passes through the unstable slope body, and the anchoring section refers to the part located in the stable slope body. The primary function of prestressed anchors is to reduce the downward force of the soil and improve the stability of the soil.
Tensile anchor
Tensile anchors mainly rely on the anchoring section to provide sufficient pull-out force to ensure the application of prestress. The anchoring section generally uses cement mortar to consolidate the anchor cable body to the stable part of the rock mass. According to whether the tension section is bonded or not, there is a full-length bonded and free-type.
Bond type
First, use pneumatic drilling or water drilling to drill the full-length, perform grouting on the anchoring section, and then perform grouting on the tensioning and tensioning sections, which can also be called secondary grouting anchors. The feature of this form of support is that the prestress is maintained even if the anchor head fails.
Free type
First, use pneumatic drilling or water drilling to drill the full-length, then grouting or grouting while drilling, and tension after grouting, also known as secondary grouting anchor. There is no need to add casing outside the anchor rod in the anchoring section, but it is necessary to add casing outside the tensioning section. The anchor rod in the tensioning section is not directly bonded to the anchor body or surrounding rock mass and will not be affected when it expands and contracts freely.
Pressure anchor
The stress mechanism of pressure anchors is different from that of tension anchors. The tensile load is directly transferred to the drill bit through the unbonded hollow anchor body, causing the grouting body to change from the traditional tensile stress state to compressive stress. Suitable for thin rods with large heads. This kind of support structure has a good anti-corrosion effect.
Split set
The split set consists of a rod body and a tray. Its mechanical characteristics are in the three-way prestressing force applied to the surrounding rock; it can provide support resistance immediately after installation, which is conducive to timely control of the deformation of the surrounding rock; the anchoring force increases with time; the anchor rod can still maintain a high anchoring force after rock displacement.
Self-drilling anchor bolt
Self-drilling anchor bolt consists of six major accessories, a hollow anchor bar, a drill bit, a coupler, a plate, a nut, and a centralizer. It integrates drilling, grouting, and anchoring into one, with a simple construction process, high construction efficiency, and good anchoring effect, which can effectively solve the problems of easy collapse and difficult hole formation during drilling. Therefore, it applies to a wide range of geological conditions, such as siltstone, miscellaneous fill, strongly weathered rock, pebble layer, and conglomerate layer.
Hollow bar
The hollow bar consists of a rod body, a plate, a nut, and a coupler (optional). After the slurry of the hollow bar is solidified, the nut can be tightened to increase the resistance of the supporting plate. A pressure zone can be formed at the rock layer close to the supporting plate, which is beneficial to control the initial deformation of rock mass after excavation and prevent broken rock blocks from falling.
Factors affecting the choice of rock bolt structure
Choosing a suitable rock bolt structure requires comprehensive consideration of many factors, including geological conditions, project scale, design requirements, construction conditions, etc.
- Geological conditions: different rock types, rock integrity, and ground stress states will affect the choice of rock bolt structure.
- Project scale and design requirements: large-scale engineering projects usually require higher load-bearing capacity and stability and need to choose anchor structures with greater load-bearing capacity. At the same time, the support parameters and safety factors in the design requirements will also affect the choice of rock bolt structure.
- Construction conditions: these include construction site, construction equipment, construction period, and other factors. When selecting a rock bolt structure, we should fully consider the constraints and influence of construction conditions. For example, when the construction site is narrow and construction equipment is limited, it may be necessary to choose simple construction and lower-cost rock bolt structures.
- Economic considerations: different models of rock bolt structures may have differences in material costs, construction costs, maintenance costs, etc. Therefore, when selecting a rock bolt structure, we should consider its cost-effectiveness and long-term economic benefits.
Selection process and method of rock bolt structure
Selecting the appropriate rock bolt structure requires following definite processes and methods. The following is a brief rock bolt structure selection process:
- Clarify project requirements and goals: including support scope, support period, support effect, etc. It helps provide clear guidance for subsequent rock bolt structure selection.
- Collection and analysis of geological data: collect geological data of the project location, including rock type, rock integrity, ground stress state, etc. Conduct a detailed analysis of these geological data.
- Develop a preliminary plan: based on factors such as geological conditions, project scale, and design requirements, develop a preliminary rock bolt structure plan. This solution can include multiple rock bolt structures for subsequent comparison and optimization.
- Comparison and optimization of plans: comparative analysis of different rock bolt structures in the preliminary plans and evaluation of their suitability, load-bearing capacity, stability, economy, etc. Based on the comparison results, refine and fine-tune the plan to determine the ultimate rock bolt structure type and parameters.
- Construction design and implementation: following the optimized scheme, carry out a detailed construction design. Including determining the length, diameter, spacing, and other parameters of rock bolts, selecting grouting materials, and determining the grouting process. Subsequently, implement construction according to the design to guarantee construction quality.
- Monitoring and maintenance: after the construction is completed, regular monitoring and maintenance of rock bolts will be carried out. Monitor the changes in the force state and other parameters of rock bolts, and discover and deal with potential safety hazards promptly. At the same time, necessary maintenance and reinforcement work is carried out on the rock bolt structure based on the monitoring results to ensure its long-term safety and stability.
Conclusion
Choosing the appropriate rock bolt structure is a critical step to ensure the safety and stability of the project. During the selection process, we must consider many factors. By analyzing these factors in detail and following scientific selection processes and methods, we can select the most suitable type of rock bolt structure. It not only helps to improve the project’s overall performance but also ensures the economic and social benefits of the project. Therefore, it is crucial for relevant engineering personnel to master the selection skills of rock bolt structures and flexibly apply them in actual projects. As technology continues to advance and experience grows, we anticipate witnessing more innovative and efficient anchor structure solutions in the future. These advancements will contribute to the ongoing development of engineering.
