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Graded gravel is a typical filler for railroad subgrade and the procedures for designing and evaluating it are crucial. The current specifications only stipulate the physical indicators of graded gravel material groups and the mechanical indications following on-site compaction. The lack of indoor mechanical standards makes it impossible to predict the on-site construction. Furthermore, the specification specifies various varieties and vast ranges of gradation, making it difficult to construct a skeleton structure. The current specification uses the heavy compaction method (HCM) and static compaction method (SCM) for the test method of graded gravel, which are no longer compatible with the current vibration compaction molding process. In this work, the effects of grading types, compaction coefficients, and water content conditions on the mechanical properties of the subgrade surface grading gravel were studied. Then the correlation between the field and indoor mechanical indexes was investigated and the K30 predictive index of graded gravel was proposed and verified by combining it with the test section. The results show that compared with HCM and SCM, the correlation between vertical vibration compaction method (VVCM) and the field was greater than 90%. Compared with standard graded gravel, the California bearing ratio (CBR), Rc , and E0 of the strongly embedded skeleton compact gradation (VGM) graded gravel can be increased by 55%, 162%, and 171%, respectively. When the compaction coefficient increases by 1%, the CBR, Rc , and E0 can be increased by 12%, 28%, 31%, respectively. Compared with graded gravel with the optimal water content, the CBR, Rc , and E0 of dry graded gravel can be increased by 7%, 94%, and 14%. The proposed CBR1 design standard, Evd acceptance standard, and graded gravel design method can better predict the K30 index on-site. [ABSTRACT FROM AUTHOR]

To control the cement-stabilised crushed gravel (CSCG) shrinkage crack and improve the road performance, analysing the composition of CSCG structure on performance influence law and cut-off of coarse and fine aggregate, the strong interlocking skeleton gradation (SISG) of CSCG based on vertical vibration test method (VVTM) was proposed and its performance was verified. The mechanical strength prediction equation of CSCG was established. The results demonstrate that 4.75 mm was the demarcation point of coarse and fine aggregates. When the coarse aggregate forms a stable framework and cement stone is completely filled in the framework, it can form SISG and reduce the shrinkage deformation. In particular, SISG includes coarse aggregates having sizes of 19–31.5, 9.5–19, and 4.75–9.5 mm in a mass ratio of 50:30:20, a fine aggregate grading I value of 0.65, and a coarse-to-fine-aggregate ratio of 65:35. The maximum dry density, CBR value, unconfined compressive strength, and splitting strength of SISG increased by ∼1.3%, 9%–17%, 4%–12%, and 4%–8%, respectively, compared with the gradation median values obtained based on the Chinese standard. Furthermore, the error between the simulated CBR values and the measured values was <7%. The proposed mechanical strength prediction equations exhibit high reliability. [ABSTRACT FROM AUTHOR]