某地铁深基坑工程，工程主体分布于富水上软下硬的复杂地质条件，设计选用三轴搅拌桩作为止水帷幕并要求三轴搅拌桩进入风化岩层，隔断基坑内外的透水层，搅拌桩如何进入风化岩是一个值得研究的技术难题。通过对三轴搅拌桩的机械选型、设计三轴搅拌桩钻头的结构形式、适用此地质条件下的施工参数等方面进行详细研究，实现三轴搅拌桩止水帷幕在泥质粉砂岩中的成功施工，达到彻底隔断透水层的目的。主要研究结论如下： 1）富水上软下硬复杂地质条件下可以选用三轴搅拌桩作为止水帷幕； 2）三轴搅拌桩入岩后，在类似地质条件下可选用钻孔桩+三轴搅拌桩代替地下连续墙作为围护结构体系，以节约投资。

The deep foundation pit under study is located in waterrich composite ground consisting soft strata at the upper part and hard strata at the lower part. Threeaxis mixing piles are designed as the waterstopping curtain of the foundation pit. The threeaxis mixing piles are required to extend into the weathered rock so as to isolate the impermeable strata. Therefore, extending the threeaxis mixing piles into the weathered rock is a technical challenge to be studied. In the paper, analysis is made on the type selection of machines for the threeaxis mixing piles, a new type of drill bit is designed for the drilling machine, and construction parameters suitable for the geological conditions are studied. Conclusions drawn are as follows: 1) Threeaxis mixing piles can be used as the waterstopping curtain for foundation pits located in waterrich composite ground consisting soft strata at the upper part and hard strata at the lower part; 2) Because threeaxis mixing piles can be extended into weathered rock, “bored piles + threeaxis mixing piles” may be used as retaining structures in geological conditions similar to those mentioned above to replace the diaphragm walls so as to reduce the investment. 