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| Model test on treatment of collapsible loess foundation of metro tunnels#br# |
| ZHANG Yuwei1，2，SONG Zhanping1，2，WENG Xiaolin3，DUAN Yuxin1，2#br# |
| (1. School of Civil Engineering，Xi¢an University of Architecture and Technology，Xi¢an，Shaanxi 710055，China；2. Shaanxi Key Laboratory of Geotechnical and Underground Space Engineering，Xi¢an University of Architecture and Technology，Xi¢an，Shaanxi 710055，China；3. School of Highway，Chang¢an University，Xi¢an，Shaanxi 710064，China) |
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Abstract Collapsible loess is sensitive to water，and floating collapsible foundation of loess tunnels is easy to cause lining cracking and other diseases. In order to guide the design of tunnel foundation treatment in loess areas，in this paper，a ground immersion model test device was developed relying on a loess metro tunnel project，the model test of surface triaxial mixing piles treating tunnel foundations was systematically carried out，and the effects of two main factors including the pile spacing and the treatment depth on treatment results were evaluated through monitoring the mechanical deformation characteristics of the tunnel structure. The results show that，the smaller the pile spacing is，the smaller the change values of the lining bending moment，axial force and earth pressure caused by foundation soaking are，while that，as the pile spacing is reduced to a certain value，the further reduction of the pile spacing will not increase the foundation treatment effect obviously. The larger the foundation treatment depth is，the more obvious the stress control of the lining structure caused by foundation soaking is. When the treatment depth reaches a certain value，however，the stress change of each point of the tunnel lining caused by soaking is not obvious，so the treatment depth only needs to reach the threshold value with a allowed amount of residual collapse. It is also indicated that the sensitivity of the stress of the tunnel structure to the treatment depth is greater than the pile spacing. When the treatment depth of the foundation reaches the threshold value，further reducing the pile spacing has no obvious effect on the treatment effect. Therefore，when dealing with the collapsible foundation of tunnels，it is suggested to first consider ensuring sufficient treatment depth of the foundation，following the principle of “long better than dense”.
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2020, Vol. 39 
