What Is Rock Bolting in Construction?

Time:2022-06-28From:sinorock View:

Rock bolting is a new technique to reinforce the unstable conditions in tunnels, slopes, mines, and foundations. It not only keeps the people and equipment safe but also ensures the construction term.

Rock bolts are not only used in mines, but also in engineering technology to reinforce the main body of slopes, tunnels, and dams. The bolt is a tension member that goes deep into the stratum. One end of the bolt is connected to the engineering structure, and the other end is deep into the stratum. The whole bolt is divided into a free section and an anchored section. The free section refers to the transmission of the tensile force at the bolt head to the anchor area, whose function is to prestress the bolt.

Rock Bolt Types

Swellex Rock Bolt

Swellex rock bolt is also called hydraulic expansion bolt. It consists of end sleeves, retaining rings, liquid injection ends, trays, and other accessories. Put the steel pipe into the bolt hole and expand it with high-pressure water. During the expansion process, the swellex rock bolt is permanently deformed, the wall of the bolt is completely fitted with the irregular hole wall of the drill hole, and the rock mass is reinforced by the friction force and self-locking force generated along the entire length of the bolt.

Expansion Shell Rock Bolt

An expansion shell rock bolt consists of an expanded shell anchor head and a hollow bolt. Usually, an expanded shell anchor head is made of high-strength steel.

The expanding shell rock bolt generates the anchoring force through the extrusion friction between the expanding shell and the inner wall of the bolt hole and can apply to prestress to fix the hollow bolt body in the center of the anchor hole.

expansion shell rock bolt

Cable Bolts

The cable bolts are that when anchored in the side holes in the suspension bridge, the main cable is divided into many strands of steel bundles and anchored respectively. These steel bundles are called cable bolts. The cable bolt is a prestressed steel strand that is fixed on the slope surface through the outer end, and the other end passes through the sliding surface of the slope and anchors in the stable rock mass under the sliding surface. The friction resistance keeps the structural surface in a compressed state to improve the integrity of the slope rock mass, thereby fundamentally improving the mechanical properties of the rock mass, effectively controlling the displacement of the rock mass, promoting its stability, and achieving the purpose of improvement of bedding and landslides and the dangerous rocks and dangerous rocks.

cable rock bolt

Self-Drilling Rock Bolts

The self-drilling rock bolt is composed of a hollow anchor bar which is divided into r thread and t thread, a drill bit, which is sacrificial, a coupler to connect two hollow bars to extend the length, a nut, a plate, and a centralizer. It can combine drilling, grouting, and anchoring in one process. The self-drilling anchor bolt system is safe, efficient, and convenient. It is suitable for broken rock, loose soil, and geological conditions where is difficult to drill holes. It helps to ensure the anchoring effect in complex ground conditions and achieve the best construction result.

self drilling rock bolt

Rock Bolt Installation Procedure

Swellex Rock Bolt

Drill a hole

Pull out the drill rod

Put the swellex rock bolt in the drill hole

Grout water to swell the rock bolt to generate friction

Expansion Shell Rock Bolt

Anchor hole ventilation inspection

drilling

Inserting the shell bolt

preload rock rod

Install Slurry Stopper, Backing Plate, and Nut

Tensioning and grouting

Cable Bolts

Drilling

During the drilling process, high-pressure water is used for flushing, and there is no stagnant water, stone powder, and gravel in the hole.

During the drilling process, if the hole collapses due to the weak and broken stratum, consolidation grouting can be carried out to solidify the wall. When drilling in the loose body of the accumulation slope, in order to prevent the hole from collapsing, the casing should follow when drilling.

Fabrication

Cut off the source of corrosion, avoid direct contact with harmful substances, and prevent moisture and corrosive gas impregnation

Installation

Before the cable bolt is inserted into the hole, re-check the through-hole of the drilled hole, and clean up or deal with the collapsed hole and dropped block.

The cable bolt that has been derusted, cleaned, and checked without any quality problems shall be slowly pushed into the hole manually. Ensure the straightness and integrity of the steel strand.

Grouting

After the cable bolt is inserted into the hole, grouting is carried out in sections, and grouting is performed once every 4 to 5 casings are pulled out.

Self-Drilling Rock Bolts

Confirm the drilling position

According to the designed vertical and horizontal spacing of the bolt, the anchor rod is positioned, and the anchor rod body is directly used as the drill rod when drilling. Confirm the drilling position according to the design drawing, and then align the drill bit with the hole.

Clean up the hollow bolt body

Before drilling, check whether the drilling rig and grouting machine are operating normally, and check whether the water hole of the drill bit and the interior of the bolt are unobstructed. Supply water to the anchor rod, and start drilling after the water flows out of the grouting hole of the drill bit. If there is any blockage, it should be cleaned first.

Drill and Grout

Before drilling, fix the anchor rod with the gripper, adjust the drilling rig afterward to make the drilling angle meets the design requirements, and then release the gripper. During the drilling process, the rod body and the grouting hole are washed with pressurized water or cement slurry prepared according to a certain water-cement ratio through the screw grouting machine, and the anchor rod is repeatedly rotated to ensure that there is no residual slag in the entire drilling hole. Grouting provides protection.

The screw grouting machine is used for grouting to achieve the effect of simultaneous drilling and grouting. When using pure cement slurry or 1:1 mortar, the particle size of the sand should not be greater than 1.0mm, and the water-cement ratio should be controlled at 0.4~0.5. Open the grouting valve and start grouting into the hole through the self-drilling hollow bolt, and stop grouting after the orifice returns to the grouting for about 1 minute.

Install the backing plate nut

After the grout is solidified, install the backing plate on the exposed section of the self-drilling hollow bolt close to the surface of the rock and soil body. The anchoring force of the hollow bolt body can be transferred to the backing plate by applying pre-tightening force, and the backing plate can be pressed to the rock. To prevent the deformation of the rock mass, it is fixed with the corresponding nut to transmit the pressure.

Conclusion

The above are the details of different rock bolt types and the rock bolt installation procedure. Above all, we can see that the self-drilling rock bolt is the most convenient one to support the broken and loose conditions.

Return The List