黄土地层浸水湿陷对地铁隧道影响试验研究

黄土地层浸水湿陷对地铁隧道结构的影响是较为突出的岩土工程问题之一,为深入研究黄土层湿陷变形对隧道衬砌结构的影响机制,通过改进长安大学离心机浸水装置和监测设备,系统开展了浸水条件下湿陷性黄土层对地铁隧道结构影响的离心模型试验,试验结果表明:地铁隧道周边黄土浸水湿陷会导致土层重度增加,隧道拱顶土层内部拱效应因湿陷而消散,土层自重压力增加且完全由隧道结构承担,从而会导致隧道结构受力和变形不利,传统的深埋隧道结构设计理论需考虑湿陷条件下拱顶土压力的不利增长因素;地铁隧道基底下黄土地基的浸水湿陷会明显诱发隧道结构的附加作用应力,但一定厚度的非湿陷性黄土或有效处理过湿陷性黄土层抵御下伏土体湿陷变形的能力不容忽略,非湿陷土层厚度越大,对于抵御湿陷变形的能力越强;隧道基底土层不均匀浸水湿陷会导致隧道拱顶部呈现受拉状态,底部呈现受压状态,隧道拱顶所承受的附加应力更大,约为拱底附加压应力的3倍,隧道基底的自重湿陷变形对隧道顶部衬砌结构所造成的破坏更严重。

Experimental research on influence of loess collapsibility on subway tunnels

The influence of immersion collapse of the large-thickness loess layer on the subway tunnel structure is one of the prominent problems in geotechnical engineering problems. To study the problem in depth, centrifugal model tests are carried out by considering two factors (collapsible loess layer around the tunnel and collapsible loess layers with different thicknesses of tunnel bottom) with the improved centrifugal field immersion devices and test monitoring equipments. The test results show that the immersion collapse causes effective severe increase of the collapsible loess layer around the tunnel, and the arching effect of soil inside the tunnel vault disappears due to collapse. The weight of earth pressure on the tunnel structure increases significantly, which has bad influence on force and deformation of tunnel structure. The traditional design theory of deep-buried tunnel should consider these negative factors. The capacity of non-collapsible loess with a certain thickness and collapsible loess layer which are treated effectively against the deformation caused by the collapsible soil layer below tunnel should not be ignored. The greater the thickness of the foundation treatment, the stronger the ability to resist the deformation caused by the collapse. The thickness of the rest collapsible layer of tunnel structure base should be considered in the design of collapsible loess composite foundation.