Abstract
Due to the thick soil layer, short backfill time, and low degree of consolidation of the soil‐rock mixture backfill in Chongqing city, metro train tunnels passing through this type of strata are prone to large settlements during operation, which greatly affects the stability of the tunnel and the safety of metro train operations. In response to this problem, the dynamic triaxial test of the soil‐rock mixture backfill under cyclic loading was carried out to study the dynamic characteristics of the soil‐rock mixture backfill under cyclic loading. The effect of initial consolidation degree, effective consolidation confining pressure, and rock content on the stiffness softening of soil‐rock mixture backfill was analyzed. The results show that the initial consolidation degree, effective consolidation confining pressure, and rock content are all important factors affecting the stiffness of soil‐rock mixture backfill under cyclic loading. As the number of cycles increases, the lower the initial consolidation degree and effective consolidation confining pressure, the faster the attenuation of the softening index, and the larger the amplitude. As the rock content increases, the softening index increases and the stiffness of the backfill changes from softening to hardening. Based on the test data, the softening‐hardening model of the soil‐rock mixture is established, which is in good agreement with the field test results. This study can provide a reference for predicting and controlling the postconstruction settlement of the metro tunnel in the soil‐rock mixture backfill.
Highlights
Soil-rock mixture backfill is a nonuniform loose soil media system with a certain rock content, which consists of high strength rock, fine soil, and pores with a certain engineering scale
The stiffness softening model of the soil-rock mixture was established based on the cyclic triaxial test data and compared with the field test data. e results of the study can provide a reference for the calculation and control of post-work settlement of metro trains in the backfill area of SRM
With the increase in the cycle number, the stiffness of the soil-rock mixture tends to be stable. erefore, this paper only suggests using the segmental function to model the stiffness of soil-rock mixture under high rock content under metro train loading
Summary
Soil-rock mixture backfill is a nonuniform loose soil media system with a certain rock content, which consists of high strength rock, fine soil, and pores with a certain engineering scale. E reduction in the strength and stability of the soil-rock mixture will cause large deformation of the surrounding rock of the metro tunnel in the backfill area [1,2,3]. Fan et al [14] used the Advances in Materials Science and Engineering discrete element method to study the strength degradation and failure mechanism of soil-rock mixture at different frequencies, dynamic stress amplitudes, and durations. There are few studies on the stiffness variation rule of soil-rock mixture under the cyclic load of actual metro trains. Most of the previous studies only considered the influence of factors such as effective consolidation confining pressure, consolidation ratio OCR, cyclic dynamic stress ratio, and vibration frequency of cyclic loading. Erefore, based on the previous studies, the author investigated the stiffness variation of soil-rock mixture under the actual metro cyclic loading. The stiffness softening model of the soil-rock mixture was established based on the cyclic triaxial test data and compared with the field test data. e results of the study can provide a reference for the calculation and control of post-work settlement of metro trains in the backfill area of SRM
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