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.