Abstract: With the rapid expansion of the urban boundary, the original mountainous area has become the urban construction land after the site preparation, which will form many deep fill areas. The later construction of pile foundation is prone to problems such as borehole forming difficulties. This article presents a case history of a municipal road project. The difficulty of drilling large diameter piles located in deep fill soil area is relatively high, and multiple borehole caving occur during the construction. Therefore, a relatively stable and reliable high-pressure rotary jet grouting pile foundation assisted drilling process is proposed. Relevant tests were conducted on site, and the results showed that the use of borehole forming auxiliary technology effectively solved the problem of difficulty of borehole forming for large-diameter pile foundations in deep fill soils. After the completion of pile foundation pouring, the effect was satisfactory. This article conducts experimental investigation on the structural parameters and related arrangements of auxiliary drilling technology through on-site experiments and proposes targeted relevant parameters.

Key words: Large Fills, Borehole Caving, Rotary Boring and Dry Operation, HighPressure Rotary Jet Grouting