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.