Abstract
Sandy pebble stratum is a typical discrete particle unstable stratum, mainly consisting of sand and pebble. However, the effect of coarse-grained content on the stability of stratum is not clear. This paper defined the sandy pebble soil of different coarse-grained content in Chengdu City, Sichuan Province, China as the research object. Research on macro-mesomechanical properties of sandy pebble soil of different coarse-grained content was carried out using the method combining the indoor large-scale triaxial test of coarse-grained soil with the discrete element numerical triaxial test. The research results showed that the stress-strain curve of sandy pebble soil exhibited strain softening with the increase of coarse-grained content; when the confining pressure was the same, the stress peak increased and the strain when the peak was reached decreased gradually with the increase of coarse-grained content. It revealed the functional relationship between coarse-grained content and mechanical indexes of sandy pebble soil such as internal friction angle and cohesion. The internal friction angle and cohesion of sandy pebble soil linearly increased with the rise of coarse-grained material; it proposed the particle discrete element micro parameters of sandy pebble soil of different coarse-grained content, including contact modulus, friction coefficient, particle stiffness ratio, contact bond strength. The research results provided the theoretical support for the new design and construction of sandy pebble stratum project.
Highlights
Sandy pebble soil is widely distributed in various regions of the world, and its mechanical properties are further complicated by the randomness of geometrical distribution of pebble and discreteness of particle
The sandy pebble stratum widely distributed in Chengdu City, Sichuan Province, China has a great impact on the construction safety of tunnel and underground engineering(Wei et al, 2008; OmaraShahestan and OmaraShastani, 2017), so the study on strength characteristics and stability of sandy pebble soil has been paid increasing attention (Si et al, 1990; Hejazi et al, 2017)
Geng Li(2011)simulated the triaxial test process using PFC3D, and analyzed the effect of particle micro parameters on the strength of coarse-grained soil, it researched on only a gradation of soil, so the conclusions were not representative
Summary
Sandy pebble soil is widely distributed in various regions of the world, and its mechanical properties are further complicated by the randomness of geometrical distribution of pebble and discreteness of particle. Many scholars believed that the physical and mechanical properties of sandy pebble soil of different coarse-grained content such as cohesion, internal friction angle and permeability had a great impact (Wei et al, 2008; Yasin et al, 2017).Most of them conducted studies on macromechanical properties of sandy pebble soil using the triaxial test and direct shear test but lacking micromechanical parameters of the composite structure of sand and pebble particles. Xu Xiaofeng (2013) et al established the calculation model of discrete element simulation of four kinds of gravelly soils of different coarse-grained content, and analyzed the effect mechanism of coarse-grained content on the macro-micromechanical properties of gravelly soil, the micro parameters obtained were only suitable for a confining pressure, so it was not accurate enough. The particle gradation of sandy pebble soil used in the test is shown in Table 1 and Figure 2
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