Self-drilling hollow grouting anchor successfully applied in slope support of hydropower station

During the excavation and support construction of high slope hydropower station, in order to speed up the project progress and protect the vegetation. The main idea of construction is to reduce the amount of excavation works and strengthen the slope support.

The maximum excavation height of the right bank slope in Yunnan Lazhai Hydropower Station is 238m. Slopes are steep. The highest slope exceeds 170m of the dam, and there are broken rocks and soil accumulations at the top. During construction, there were problems such as seriously collapsed holes, stuck drills, and slow construction progress. Self-drilling hollow grouting anchor integrates drilling, injection, and anchoring, and does not need to be taken out after drilling, which avoids the phenomenon of hole collapse. The cement slurry entered through the hollow pipe and quickly solidify to provide anchoring force in time and ensure the surrounding rock complete and stable. The self-drilling anchors is suitable for complex terrain conditions especially weak and broken surrounding rocks. It can change the surrounding rock conditions and achieve ideal supporting effects. Therefore, self-drilling anchor system was adopted for support to speed up the construction progress and ensure the construction quality.

Strict control of the drilling process is a key process to realize the integrated function of self-drilling anchor bolts. There are 3 aspects that you need to pay attention:

1、Before drilling, check whether the hollow bar and the holes of drill bit are unimpeded to avoid blockage by foreign objects.
2、Because the construction area contains cataclastic rock or loose soil, the debris generated during drilling is difficult to discharge. In addition to thoroughly clean the borehole with high-pressure air, you can also wash the holes with water. The water can cool down the drill bit simultaneously, which further improves the drilling quality.
3、Due to the different topography and layer structure, the high slope of the Lazhai Hydropower Station was divided into multiple areas during construction, and 3 drilling depths of 6-9m, 9-12m, and 12-15m were set. In order to facilitate the construction, the single length of the self-drilling bolt is usually 3 meters. During drilling, the coupler was used to lengthen the hollow bar and achieve the design depth. The coupler and the tool connecting drill rig and hollow bar have high torque and easily damaged, which should increase inventory to ensure the project progress.

The use of self-drilling hollow grouting anchors and strict control of construction procedures have enabled the completion of the high slope support project of Lazhai Hydropower Station. The success of the project confirmed that self-drilling hollow grouting bolts not only improve the overall stability of weak and broken surrounding rock through pressure grouting but also not affected by the collapse during drilling, which has great significance for guiding the construction of similar projects. 

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