三轴搅拌桩入岩施工技术

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。

Construction Technology for Three-axis Mixing Piles

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. 