Abstract: This study determined the reasonable treatment range of utility tunnel foundation in self-weight collapsible loess with large thickness. Meanwhile, the regularity of the compacting effect on the foundation was revealed with various treatment depths, and the infiltration law and settlement characteristics of composite foundation after immersion were analyzed. With different depths of lime soil (pure soil) compaction piles, the foundation treatment experiments were conducted on the collapsible loess with large thickness. Moreover, post-work immersion tests were carried out by embedding TDR moisture meter and layered settlement instrument. The results show that with increasing the treatment depth of composite foundation, the impermeability of composite foundation, compacting effect and dry density of soil between piles all increase. The external water presents distinct multistage infiltration in composite foundation, including four stages basically. The deformation of wetting soil between piles decreases with the increase of the foundation treatment depth. Besides, it shows obvious five stages. According to the research results, under the condition of effective waterproof measures, the reasonable treatment range is summarized as follows: the treatment depth should be controlled in the range of 9-12 m, and the treatment width should be controlled within 2 m extended from each side of tunnel.

Key words: self-weight collapsible loess with large thickness, utility tunnel foundation, compaction piles, reasonable treatment range, post-work immersion test, infiltration law