黄土隧道地基湿陷变形评价方法探讨

 隧道穿越自重湿陷性黄土地层时，可能遭受浸水作用下地基湿陷变形的附加作用而产生结构破坏。针对隧道衬砌结构的湿陷性黄土地基，结合隧道围岩及地基的自重湿陷变形特征，首先，提出浅埋隧道围岩压力、衬砌结构自重荷载构成基底压力和隧道两侧基底面分布土层自重共同作用下地基土的附加应力计算方法，以及考虑地基土自重应力的湿陷压缩应力计算方法。其次，在基本物性与构度、构度与结构压缩屈服应力、孔隙比和初始孔隙比比值与压缩应力和结构压缩屈服应力比值关系的基础上，建立自重湿陷系数和湿陷系数的计算方法。依据大厚度自重湿陷黄土场地不同埋深范围黄土具有不同自重湿陷系数门槛值的特征，得到了场地的自重湿陷变形和隧道地基的湿陷变形的计算方法。最后，通过数值计算分析，模拟隧道地基湿陷变形不同沉降差作用下衬砌结构应力场和塑性域发展，随着不均匀湿陷变形的增加，隧道衬砌结构塑性区范围不断增大，并结合铁路路基沉降控制标准，建议隧道地基湿陷变形0～5 cm为一级、5～10 cm为二级、大于10 cm为三级。

Collapse deformation evaluation method of loess tunnel foundation

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.