Common Failures For Hollow Anchor Bar Tunnel Construction

Time:2022-11-26From:sinorock View:

Anchor bolt is one of the important supporting methods to maintain the stability of surrounding rock and ensure construction safety during tunnel construction. To a certain extent, it can also function as part of a permanent support structure after construction is completed. Therefore, how to ensure and check the construction quality of anchor bolts, and how to strengthen quality control and management is very important.

Common Failures For Hollow Anchor Bar Tunnel Construction

1. Incorrect water-cement ratio. On-site test personnel and supervisors should measure the consistency of cement slurry and make sure it meets the design requirement. If the water-cement ratio is not up to standard, it is mostly due to the use of less cement, or cement agglomeration and uneven mixing.

2. Horizontal angle of anchor rod set. At present, drill jumbos are mostly used for drilling. The height and direction of the drill jumbos cannot be adjusted. Ordinary drill jumbos are long and often push up to the top platform. In this way, the hollow anchor bars at the position above the spandrel are easy to drive into the rock and soil at a horizontal angle, and cannot be perpendicular to the excavation contour line, resulting in a very common phenomenon of roof leakage at the vault position.

3. Large positioning deviation of the hollow anchor bars, and insufficient hole depth. The construction personnel did not lay out the lines, mark, and fix the points by themselves according to the regulations, but drilled holes by intuition, resulting in a large deviation in the hole position. The site shall be randomly inspected, and the number shall not be less than 10% of the total bars.

4. Insufficient grouting. Insufficient grouting is mainly because the grout stopper is not tightly plugged, resulting in large pores and insufficient pressure. Or because the drill holes are not blocked in time after the grouting was terminated, causing the grout to flow back.

Construction Process Management

1. Staffing

To ensure the construction quality of hollow grouting anchors, at least two construction workers and one tester should be assigned to each hole during construction. The whole process of on-site hole positioning, drilling angle, row spacing, drilling depth, anchor rod insertion, grouting mix ratio, and grouting situation should be monitored.

2. Raw material inspection

The construction site laboratory should conduct a sampling inspection of materials in time, and determine whether they can be used in engineering entities according to the sampling inspection results. During the construction process, the tester should also continue to track the pile number and location of each batch of materials to accumulate original data for traceability.

3. On-site equipment testing

On-site management personnel should be equipped with: LED rechargeable searchlights, steel tape measure, spirit level, consistency meter, mold testing, and other equipment, and the drawings should be carried with them for future reference.

4. Inspection of cement slurry consistency

When the water-cement ratio is 0.4-0.5, the consistency of the cement slurry should be 28-30 seconds (need to be determined by test). During the construction process, the tester should often check the consistency of the slurry, and if it does not meet the requirements, should immediately find out the cause and correct it on the spot.

5. Inspection of the grouting process

The pressure of the grouting should be kept at 0.3MPa.

When the grouting pump is turned off, the grouting phenomenon between the plug and the surrounding rock should stop in a short time and no more grout leakage, otherwise it proves that the grout-stopping effect of the plugs does not meet the requirements, and re-positioning and grouting are required.

Summary

Hollow anchor bars are used more and more in tunnel construction. The selection of high-quality hollow anchor bars and standardized construction are important factors to ensure the safety of tunnel construction. As a professional anchor bolt manufacturer, the self-drilling hollow anchor bar from Sinorock has a good supporting effect and has been applied in many tunneling projects. Welcome contact: sinorock@sinorockco.com.

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