Collapse deformation evaluation method of loess tunnel foundation
SHAO Shengjun1，2，CHEN Fei1，SHAO Shuai1
(1. Institute of Geotechnical Engineering，Xi'an University of Technology，Xi?an，Shaanxi 710048，China；2. Shaanxi Key Laboratory of Loess Mechanics and Engineering，Xi'an University of Technology，Xi?an，Shaanxi 710048，China)
Abstract：When tunnel passes through a self-weight collapsible loess stratum，lining structure of loess tunnel may be destructed by the additional collapse deformation of loess upon water immersion. In this paper，the surrounding pressure of loess tunnel，the characteristics of the self-weight collapse deformation of collapsible loess tunnel foundation，and the destruction of lining structure caused by the collapse deformation of foundation are discussed. Firstly，a calculation method for the additional stresses of foundation soil under the surrounding pressure and weight of lining structure and under soil self-weight stress of both sides of tunnel was proposed. The collapsible compression stress is obtained by the additional stresses adding the soil weight under foundation. Secondly，the relationships between the structural index and physical index，between the structural index and structural yield stress，and between the ratio of void ratio to initial void ratio and the ratio of compressive stress to structural yield stress were used to establish a calculation method for the collapsible coefficient and self-weight collapsible coefficient of loess by comparing the confined compression curves of loess in natural moisture content and in saturation. According to the fact that the loess at the different depths has the different threshold values in the region with thick layer of self-weight collapsible loess，the self-weight collapsible deformation of the site and the collapsible deformation of the tunnel foundation are derived. Finally，the different collapsible deformations of tunnel foundation，the stress fields and plastic region of lining structure were analyzed numerically. The larger the settlement difference is，the more extensive the range of plastic region is. Three grades of collapse deformation of tunnel subgrade，0–5，5–10 cm and more than 10 cm are proposed according to the control standard of railway bed.
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2017, Vol. 36 
