Self Drilling Anchor Bolt VS Long Pipe Shed, Which Is Better to Support the Tunnel?

In recent years, as a new type of support system, self-drilling anchor bolts have been more and more widely used in various geotechnical anchoring projects. For a long time, long pipe shed support has been the preferred solution in tunnel support projects. However, as more and more tunnel support projects become more and more difficult, it seems difficult for long pipe sheds to meet the increasingly complex geological conditions, especially for geological conditions such as soft and broken surrounding rocks and strongly weathered rocks. The support scheme is difficult to construct, so there are more and more construction cases of self-drilling anchor bolts as tunnel support pipe sheds.

self drilling anchor bolt system
Self-drilling anchor bolt, also called self-drilling rock bolt, self-drilling hollow bar, or sda bolt, contains a hollow bar, a drill bit, a coupler, a plate, a nut, and a centralizer. There are two types of hollow bars, R thread and T thread. And various drill bits are available according to the different conditions. There are several features that help to make self-drilling anchor bolt of our most reliable solutions, the most notable being the 'all-in-one' tool, or simultaneous grouting. 
So, self-drilling rock bolt support or long pipe shed support, which is the best choice for tunnel advanced support? Below, we compare the advantages and disadvantages of self-drilling bolt support and long pipe shed support from the construction process.

self drilling anchor bolt system
Self-drilling bolt construction process
1) Before construction, check whether the hollow bolt body and related accessories and rock drilling and grouting machinery are normal, and after ensuring that they are normal, connect the rock drilling equipment to the self-drilling bolt correctly;
2) Determine the drilling position and drilling angle;
3) Start the drilling construction according to the predetermined position and angle, rinse the inner hole of the self-drilling anchor rod with water, then connect the rotary grouting adapter to the end of the anchor rod, and grouting while drilling, if a single self-drilling anchor rod The length cannot meet the design requirements, and the length of the connection socket can be used;
4) After drilling to the design depth, the drilling rig can be operated to make the self-drilling anchor rod go up and down and reciprocate to ensure that the thickness of the slurry around the drill rod is uniform;
5) Finally install the backing plate and nut.

self drilling anchor bolt system
Long tube shed construction process
1) Use reinforced concrete arch to make the guide wall of long tube shed;
2) Accurately measure the plane position, inclination angle and extrapolation angle of the orifice tube and number them one by one;
3) Use the electric drilling rig to drill according to the predetermined position. During the drilling process, ensure that the drilling elevation angle is between 1° and 1.5°, and the maximum subsidence and left and right offset of the drilling rig do not exceed 1% of the length of the steel pipe;
4) After drilling a hole, pull out the drill pipe, and then push into a steel pipe. During drilling, the deflection should be measured in real time. If it exceeds the design requirements, the deflection should be corrected in time;
5) Connect the hollow steel pipe to the grouting pump for grouting; before grouting, the grouting field test should be carried out, and the grouting parameters should be determined according to the actual situation according to the test to ensure that the slurry diffusion radius is not less than 0.5 meters.
From the construction process of the above two construction schemes, we can clearly see that the construction process of the long pipe shed is much more complicated and more difficult than the self-drilling bolt. Moreover, in the case of loose geological engineering, the long pipe shed support cannot be formed into holes, and only self-drilling anchor bolts can be used for construction.
Self-drilling anchor bolts have many other advantages as a tunnel advance support pipe shed.
The length of the self-drilling bolt is easier to adjust: it can be cut off at any position or lengthened by connecting sockets, and it has good sealing performance and will not leak slurry;
Self-drilling anchor bolts can be applied to most geological structures, especially weak, broken and other difficult pore-forming geology, such as fault fracture zone, weathered rock, gravel soil stratum, sand and pebble stratum, etc.;
The construction method of self-drilling anchor bolts is simple: when drilling and construction in different geology, the installation methods and construction methods of self-drilling anchor bolts are almost the same and do not require professional technicians;
Self-drilling anchor bolts have high construction efficiency: self-drilling anchor bolts use the bolts as drill pipes and grouting pipes, which will not be retracted after drilling into the stratum, reducing construction procedures, improving construction efficiency and shortening construction period.
So, it is apparently we can see that the self-drilling anchor bolt is much better than a pipe shed when supporting the tunnel.

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