Abstract:

In order to study the water infiltration and self-weight collapse deformation characteristics of Jingyuan loess with large thickness under the condition of immersion, a field immersion test without water injection holes was carried out in the self-weight collapsed loess site of Jingyuan North Station along the Zhongwei−Lanzhou Railway. The surface and underground collapsible deformation, cracks, water content and vertical stress in the soil around the test pit were monitored and analyzed. The water diffusion, self-weight collapsible characteristics and vertical stress in the soil were studied, and the regional correction coefficient β₀ value and wetting angle were discussed. The results showed that: the change of volumetric water content was divided into four stages: immersion stabilization (two), rapid increase (one) and slow increase (one). In the immersion process, the vertical infiltration of water was accelerated and the radial diffusion was slowed down at 21 m, and the final shape of the wetting front was presented as elliptical. According to the water content test results of exploratory wells and boreholes, the maximum wetting angle was calculated to be 41°. The self-weight collapse process of loess in the site went through three stages: severe collapse, slow collapse and consolidation stabilization. At the end of the test, a total of 13 ring cracks were developed, and the farthest point of the cracks was 26 m from the edge of the test pit. According to the laboratory test and field test results, it was suggested that the regional correction coefficient should be corrected along the depth of the soil layer, and the β₀ value was taken as 1.05 within 0−10 m and 0.95 within 10−27 m. In the depth range from the surface to 21 m, the foundation soil was saturated and fully collapsed. The vertical stress in the soil increased linearly along the depth, and the vertical stress in the soil was close to the saturated self-weight stress. The foundation soil below 21 m failed to collapse entirely, and the vertical stress in the soil decreased gradually. The research results could be applied to the later construction of Zhongwei−Lanzhou Railway and provide a reference for other regional engineering projects.

Key words: large-thickness loess foundation, water immersion test, collapse deformation, regional correction coefficient β0, water diffusion, vertical stress in soil