3 Reasons Why Self-Drilling Rock Bolts Can Replace Cables

Rock bolts have been used more and more in the field of geotechnical engineering, among which self-drilling hollow rock bolt support is an important reinforcement technique in geotechnical engineering. The self-drilling hollow bolt combines drilling, grouting, and anchoring into one process. It has the characteristics of high construction efficiency and is of a good anchoring effect. It is suitable for different kinds of geological conditions, especially the conditions that are hard to drill holes. According to the construction situation, it can replace conventional rock bolts, anchor cables, and other products.

In the construction of the foundation support of Shuangshan Station of Qingdao Metro Line 3, the technical application of self-drilling rock bolts successfully replaced anchor cables. Shuangshan Station is located on the west side of Heilongjiang Road at the intersection of Heilongjiang Road and Hefei Road in Sifang District, Qingdao City. The main body of the station is constructed by the open-cut method, and the support structure initially adopts three forms, namely: bored piles + steel pipe inner support system, bored pile + anchor cable system, and hanging foot pile. Among them, the following problems occurred during the construction of the anchor cable system at the end of the large mileage end of Shuangshan Station and the right line of K13+686.396 ~ K13+740.796:



1) Due to the complex geological conditions and the development of rock fissures, during the drilling process, the air leakage in the stratum is serious, so that the rock powder in the hole cannot be blown out of the hole, which often causes the stuck. Once stuck, it must result in construction delaying. What’s worse, if this situation can’t be handled properly, the hole will collapse.

2) After the holes are formed, it is very easy to collapse, and the adjacent holes are easy to string holes, which makes it difficult to place the anchor cable.

3) The boundary between the soil layer and the rock layer in the construction site is obvious. When the anchor cable penetrates to the boundary point, the guide cap cannot move forward in the direction of the original hole, so the anchor cable cannot be fully inserted.

4) Poor geological conditions, many rock fissures, abundant groundwater, and insufficient anchor cable grouting.

In view of the above situation, the construction party decided to replace the anchor cable with a self-drilling anchor rod for testing. Through construction, the self-drilling rock bolt effectively solves the problems of easily collapsed holes, insufficient grouting, stuck drilling, and low rework efficiency. Compared with the anchor cable, the self-drilling rock bolt has the following advantages:

Self-drilling rock bolt is mainly composed of a hollow bar, a coupler, a sacrificial drill bit, a nut, a plate, and a centralizer. The anchoring system has the characteristics of drilling, grouting, and anchoring simultaneously. During drilling, a high-pressure pump can be used to grout through the hollow channel of the bolt, and the grout can fill cracks, and consolidate rock mass and soil layer. The surface of the bolt body is full-length threaded, which can make the mortar and the bolt better bond, and effectively avoid the phenomenon that the grouting is not full. And the bolt body does not need to be pulled out after drilling, so the problem of easy-to-collapse holes is also solved.



The self-drilling rock bolt system integrates drilling, grouting, and anchoring together. The casing pipe is omitted in the construction. Compared with the construction technology of drilling, insertion, and grouting of the conventional bolt and anchor cable greatly improves the construction efficiency. Shorten the construction period and reduce the overall cost of construction.

Compared with the conventional drill pipe, the self-drilling hollow bolt is equipped with a variety of drill bits, which can be selected according to the properties of different rock layers and soil during construction. Choosing a suitable drill bit for drilling can avoid sticking and achieve better results.

The application of self-drilling rock bolt has successfully solved the technical difficulties that holes are not easily formed in the broken rock mass of Qingdao Metro Shuangshan Station, ensuring the safety of foundation construction and the progress of subway construction. Since the quality and progress of the project are guaranteed, the frequency and cost of rework and rush work are reduced, and the project investment is saved. It is successfully verified that the self-drilling rock bolt can effectively replace the prestressed anchor cables and general steel bars, and it is a reliable new anchoring technology with wide application prospects.