Abstract: Recently, the construction project department for the 220 kV supporting transmission line of the Shanghai-Kunming Passenger Dedicated Line, undertaken by Hunan Provincial Power Transmission and Transformation Engineering Company, made a bold attempt and successfully introduced new equipment—the water jet drilling rig—effectively improving rock foundation pit excavation efficiency and adding new momentum to the project's foundation construction.

Application of the water jet drilling rig in rock foundation pit excavation

    The line is located in the Zhijiang and Xinhuang areas of Huaihua City, where the foundation pit soil is mostly red rock and sandstone. The original plan was to use blasting construction, but this type of rock soil can disperse the energy generated by blasting, so blasting has little effect on it. In addition, blasting cannot be used near live lines and residential areas, so only an air compressor driving a pneumatic pick could be used for excavation, but construction efficiency was low. “Near the residential area, we have a 14-meter-deep rock foundation pit. From the start of construction until now, we have been chiseling with a pneumatic pick, and in more than 30 days we have dug only 10 meters deep,” one construction team leader said with deep feeling.
    With the year-end approaching and progress hindered, the company's on-site project department felt tremendous pressure. After searching everywhere for advanced construction methods for excavating red rock and sandstone foundation pits and repeatedly discussing various schemes, the project department finally decided to introduce a water jet drilling rig for foundation excavation.
    This was a completely new attempt. A task force formed by technical personnel from the project department stayed at the construction site to explore the equipment's operation, and their only operating experience came from online videos. After many studies and tests, the equipment finally began drilling recently. As the drill bit rotated rapidly, bowl-sized stone columns were successfully removed from the foundation pit one after another. “Hard work pays off.” The successful use of the new equipment was nearly three times faster than traditional pneumatic pick chiseling, which excited everyone on site. It is believed that before long, once the equipment is used proficiently, the efficiency of rock foundation pit excavation will be even more remarkable.