Construction Sequence of Sinorock Self-drilling rock bolts

by Hollow Bar Web Designer

With either self-drilling rock bolts installation method, gaps between the lagging and the retained ground must be backpacked to ensure good contact. Prior to placing subsequent lagging a spacer, termed a “louver”, is nailed to the top of the lagging board at each end of the lagging. This louver creates a gap for drainage between vertically adjacent lagging boards.

The size of the gap must be sufficiently wide to permit drainage, while at the same time disallowing the retained soil to fall out from behind the boards. Typically, placing vertically adjacent lagging boards in close contact is considered unacceptable, however, some waterproofing methods may require that the gap between the lagging boards be eliminated. In this case, the contractor must provide an alternate means to provide drainage.

Concrete lagging has been used, but its use may be problematic due to difficulties in handling and very tight tolerances on the horizontal and vertical positioning of the soldier beam to ensure easy installation of standard length concrete lagging. Trimming of concrete lagging is very difficult and field splicing is not possible. Also, the concrete lagging near the anchor location may crack during anchor testing or stressing.

Top-down installation of self-drilling rock bolts continues until the excavation reaches a level of approximately 0.6 m below the design elevation of a ground anchor. At this point, the excavation is halted and the ground anchor is installed. Deeper excavation (i.e., greater than 0.6 m) below the level of a ground anchor may be required to allow the anchor connection to be fabricated or to provide equipment access. The wall must be designed to withstand stresses associated with a deeper excavation.

The anchor is installed using appropriate drilling and grouting procedures, as previously described. When the grout has reached an appropriate minimum strength, the anchor is load tested and then locked-off at an appropriate load. Excavation and lagging installation then continues until the elevation of the next anchor is reached and the next anchor is installed. This cycle of excavation, lagging installation, and ground anchor installation is continued until the final excavation depth is reached.

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