| Crushed rock aggregate (CRA) are widely used in transportation constructions including railway ballast, pavement material and dam fillings. With the development of highway and railway in cold regions like Qinghai-Tibet plateau, CRA has been successfully utilized in Crushed Rock Subgrade (CRS). Because of the porosities between particles, heat convention can happen to cool the subgrade and protect the underlying frozen ground. In order to ensure sufficient porosities, large sized and uniformly graded aggregate has been generally adopted, which may reduce the stability of the subgrade. Intensive studies have been performed, both experimentally and theoretically, on the cooling effect of crushed rock subgrade, such as determining the optimal gravel size and laying position, and many researchers at the same time focused on the mechanical behavior of the well-graded CRA, however less attention was paid on the mechanical characteristics of uniformly CRA.Supported by the National Natural Science Foundation of China (No.41371081) and the National 973 Project of China (No.2012CB026104), researches on the cooling mechanism and mechanical behavior of CRA were first reviewed and summarized in this paper, large scale direct shear tests, large scale triaxial tests and Particle Flow Code (PFC) calculations were then conducted to study the strength, deformation and degradation behavior of CRA. The results can provide reference for further research and guidance for the design and construction of CRS in cold regions. The main scope of this paper can be summarized as follows:(1) Based on the large-scale temperature-controlled direct shear system, the strength, deformation and degradation response of CRA was studied, the influence of many factors was investigated. The results showed:the strength envelope of CRA was nonlinear; shear dilation was always observed after the initial compression; the relative breakage potential can be employed to evaluate the degradation of CRA. The dry density of the aggregate, fines content, moisture content and test temperature were all proved to have profound influence on the shear strength of CRA.(2) PFC was utilized to establish the direct shear Discrete Element Method (DEM) model of CRA, which was validated by comparing the simulation results with experimental results, the micro-mechanical properties, including the distribution and evolution of contact forces and displacement vectors were then investigated.(3) Many triaxial tests were conducted to further study the strength behavior of CRA, and PFC triaxial shear test models were also established. The influence of micro-parameters on the macro-response of CRA was discussed.(4) The influence of void ratio on the shear strength of CRA was investigated, and effective void ratio es was proposed to evaluate the void states of gap-graded aggregate. With the clump logic in PFC2D, a randomly-shaped particle generation method was proposed, and the Angularity Index (AI) was modified and adopted to evaluate the influence of particle shape on the shear strength quantitatively. The results showed:the shear strength and apparent friction angle increased with AI and decearsed with void ratio and es.(5) The permanent deformation and resilient response of CRA under cyclic loading triaxial shear condition was studied both experimentally and numerically. The results showed the permanent deformation increased with the amplitude and frequency of the cyclic load but decearsed with confining pressure; with decreasing crushed rock content, permanent deformation increased while resilient modulus Mr decreased; permanent deformation also deceased with AI while MR saw an opposite trend. |
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