湿陷性黄土隧道的工程性质分析

黄土隧道往往具有特殊的湿陷性黄土围岩和干旱半干旱气候地区特殊的地形地貌及地质环境，对隧道结构构成了潜在的不利影响。在对湿陷性黄土隧道修建和运行中工程特性认识的基础上，首先，根据地形地貌、地层结构、侵蚀发育、地下水条件和黄土浸水水源，进行了隧道的岩土环境等级和浸水等级划分，以及湿陷性黄土隧道的环境等级划分。其次，给出了隧道黄土地基湿陷变形量的计算分析方法，依据黄土地基湿陷变形不均匀沉降对衬砌结构的作用影响，以及列车运行对路基沉降变形的控制标准和建筑地基湿陷变形对结构的作用影响，确定了隧道湿陷性黄土地基等级的划分标准。最后，考虑到现行《湿陷性黄土地区建筑规范》适用的局限性，结合湿陷性黄土隧道的工程特点，针对隧道施工过程中围岩稳定性和湿陷变形对衬砌结构影响的两个重要问题，相应的提出了隧道地基湿陷性变形的评价方法和围岩压力的确定方法；由竖向压缩应力系数确定湿陷压缩应力，结合试验得出的湿陷系数计算隧道下地基土在实际压缩应力条件下的湿陷变形量。在考虑黄土结构性的条件下，利用太沙基公式计算隧道围岩压力，得到了围岩压力随黄土构度的变化关系。

Engineering properties of collapsible loess tunnel

The collapsibility of loess and, the arid and semi-arid climate, complicated landform and topography, and particular geological environment in loess zone potentially have adverse effects on the structure of loess tunnel. Based on the engineering properties of collapsible loess tunnel in the process of construction and operation, this paper presented classification standards for the geotechnical environment, water-immersion environment, and integrated environment of loess tunnel, according to different landform, topography, stratigraphic structure, erosion degree, subsurface water, and surface water source conditions. Furthermore, computed analysis method for the collapse deformation of loess tunnel foundation was proposed. According to differential settlement of loess foundation acting on lining structure, control standard of subgrade settlement during train movement, and influence of collapse deformation of building foundation on structure, classification standard for the foundation of collapsible loess tunnel was put forward. Moreover, considering the application limitation of present “Code for Building Construction in Collapsible Loess Zone” and the engineering properties of collapsible loess tunnel, assessment method for the collapse deformation of loess tunnel foundation and computed method for confining pressure were presented, respectively, corresponding to the stability of surrounding rock during construction and the influence of collapse deformation on lining structure. Collapsible compression pressure can be determined by the coefficient of vertical compression pressure, and the collapse deformation of tunnel subsoil thus can be calculated with the experimental coefficient of collapsibility. Introducing structural index in the Terzaghi equation of surrounding rock pressure, relationship between surrounding rock pressure and structural index was analyzed.