In today’s civil engineering field, rock bolts penetrate deep into the ground to reinforce the rock and soil mass, improve its load-bearing capacity and stability, and provide safe and reliable support for various buildings. Rock bolt support, as an effective reinforcement technology, has found widespread application in diverse geotechnical projects.
What is a rock bolt?
Rock bolts are a fundamental part of tunnel support in contemporary coal mines. They reinforce the surrounding rocks of the tunnel and play a supporting role. It is attached to the engineering structure at one end, and the other end is deep in the stratum, which is a tensile member. The whole anchor contains an anchoring section and a free section, which consists of a pallet, anchor, nut, and washer.
The supporting function of rock bolt
Suspension effect
The suspension function employs rock bolts to suspend a weak or unstable upper stratum directly from a more robust existing roof above it. Alternatively, rock bolts link loose rock blocks, often resulting from tunnel excavation to the intact and solid rock outside the loosened area. This method serves the purpose of preventing the potential collapse or falling of these loose rock blocks. In essence, the suspension function of rock bolts contributes to maintaining stability and safety in underground or excavation environments by securing weaker or potentially hazardous rock formations.
Composite beam function
The composite beam function involves leveraging the tensile force generated by rock bolts to create a composite beam structure for support. Its essence is to increase the friction between the layers by squeezing the layers considered as stacked beams through the pre-tensioning stress of the rock bolts. At the same time, the rock bolt also provides a definite shear resistance to prevent dislocation between layers. The rock bolt acts as a similar rivet, combining multiple thin rock layers into a unified composite beam. In this scenario, the anchored rock layer takes on the characteristics of a composite beam. This approach ensures that all anchored layers maintain synchronous deformation, significantly enhancing the bending stiffness of the roof rock layer.
Carving effect
It refers to the presence of one or more sets of non-continuous surfaces within the surrounding rock. The purpose is to use anchors that traverse these non-continuous surfaces to hinder or diminish the movement of the surrounding rock along these gaps or fractures. In essence, the anchoring process helps prevent or reduce displacement or shifting of the rock mass along these specific non-continuous surfaces, contributing to enhanced stability and support in geotechnical applications.
Extrusion reinforcement
This action forms a cone-shaped compression zone with the rock bolt head and fastening end as the apex. For example, if the rock bolts are arranged radially at certain intervals along the perimeter of the arched tunnel, under the action of prestress, the cone-shaped compression zones formed around each rock bolt overlap and connect, forming a continuous compression zone in the surrounding rock. Let it maintain its stability and withstand the ground pressure and the organization of the upper part of the surrounding rock loosening and deformation.
Reduced span effect
If the unstable roof rock layer is considered to be a superposition beam supported in two gangs, depending on the rock bolt suspended in the old top for the fulcrum, the installation of the rock bolt is equivalent to the place to play a point column to increase the fulcrum and reduce the span of the roof, thus reducing the bending stress and deflection of the roof rock layer, maintaining the stability of the roof and rock, so that the rock is not easy to deform and damage.
The supporting function of rock bolts does not exist in isolation. It is a comprehensive function that complements each other. It is just that under different geological conditions, the status of a type supporting function is different.
Rock bolt support form
Single rock bolt reinforcement of the rock body to form a local stress bubble around the rock bolt, group rock bolt reinforcement, as long as the spacing is appropriate, the stress bubbles overlap each other to form a uniform stress band within the rock body that is the bearing circle reinforcement zone. Rock bolt support should depend on the rock’s hardness, integrity, joints, ground stress, service life, and whether by dynamic pressure and other factors to determine a reasonable form of rock bolt support.
Currently, the commonly used rock bolt support combinations include rock bolt (cement pallet) + metal mesh; rock bolt (steel pad pallet) + steel strip; rock bolt (steel pad pallet) + steel beam; rock bolt truss; rock bolt (cement pallet) + anchor cable; it can also include rock bolt shotcrete (anchor shotcrete), anchor cable, and other combinations, the specific use the form of support depends mainly on geological conditions.
Currently, the most widely used anchors include resin anchors, self-drilling anchor bolts, split sets, etc.
Conclusion
The core of rock bolt support lies in the artificial reinforcement of the fractured rock mass, enabling it to generate reaction forces while undergoing displacement until a stress balance is formed. As an effective geotechnical reinforcement technology, it improves the stability and safety of the project by strengthening the geotechnical structure. With the continuous advancement of science and technology and the deepening of engineering practice, rock bolt support technology will continue to innovate and develop, providing safer and more reliable support for various geotechnical projects.
