Frost-heave characteristics of saturated lean clay fillers by orthogonal test design considering the static surcharge

With the increase in speed and axle load of heavy-haul trains in China, the frost heave of subgrades in seasonally frozen regions is increasingly becoming hazardous to operation. Nevertheless, the effect of the quasi-static surcharge of heavy-haul railways on the freezing characteristics of subgrade fillers has not yet been completely understood. In this study, frost-heave L9(34) orthogonal tests were conducted in open and closed systems, considering the static surcharge, dry density, and step-cooling path, to investigate the freezing characteristics of the lean clay. The external water supply creates a shallow frozen depth and a terrific frost heave for high-frost-susceptibility lean clay. The analytic hierarchy process, combined with the L9(34) orthogonal test, can quantitatively calculate the impact weights of the test factors on the frost index. The impact weights of the step-cooling path on the frozen depth and frost heave ratio were both maxima in the two systems. The impact weight of the dry density increases with the water supply, accompanied by a decreasing impact of the static surcharge. The static surcharge, which increased with the axle load, did not play a crucial role in the three test factors. The optimal level of the static surcharge for the frost heave ratio is 60 kPa, and the optimal level of the step-cooling path varies with cold temperature owing to water supply. The impact weight and optimal-level combination results of the test factors show that practical and reasonable countermeasures should be adopted in the engineering field.