Common quality problems in rock bolts construction

 In the current tunnel support systems, as a very effective support method, rock bolt has been widely used in recent years. Rock bolt can not only stabilize the surrounding rock in the construction process, but also play a role as a part of the permanent support structure after the construction, so it is very important to ensure the construction quality of rock bolt. However, the current construction situation in China has the following quality problems:

1. The water cement ratio is not correct and cement dosage is insufficient. Field testers and supervisors should often measure the consistency of cement slurry to avoid the problem of less cement, caking or uneven mixing.

2. Rock bolt is set at a horizontal Angle. Due to most rock bolts are set up using drilling rigs. The direction of the drilling rig cannot be adjusted, and the rock drill is often pushed against the drill rig platform. Mean time, rock bolt above the arch shoulder is easy to be made into a horizontal angle, and cannot be made vertical with the excavation contour line, which makes the phenomenon of roof leakage in the arch part very common.

3. The positioning deviation of rock bolt is large and the hole forming depth is insufficient. Construction workers by intuition, not in accordance with the provisions of the line, marking, fixed point, resulting in large deviation hole position. Spot check should be random, the frequency is not less than 10% of the rock bolt total number.

4. The number of anchor rods is insufficient. A check should be made before grouting of rock bolt, and a check again after all grouting is completed. Finally, construction workers should be counted again before the initial spray. The site manager must be familiar with the design drawings and the number of rock bolts to be set in each cycle.

5. No grouting or not full grouting. Non-grouting means is inserting the anchoring agent into the grouting port of rock bolt, resulting in a false grouting phenomenon. Check whether there is grouting overflow around the stop plug of the orientation, or judge whether the grouting has been done by tapping the rod body through sound. Grouting is not full mainly stop grouting plug is not tight, resulting in a too large pore, insufficient pressure. Or stop grouting, the anchor port is not blocked in time, resulting in cement slurry backflow.

The above quality problems seriously affect engineering safety and must be eliminated. The constructors must strictly follow the standardized operating procedures to carry out the construction, and the on-site management should also conduct supervision and inspection. Only in this way the rock bolt can perform as an effective form of support to ensure construction safety.

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