Mechanical responses of subgrade with natural hard crust through an accelerated laboratory loading test on pavements model

Abstract

Natural Hard Crust (NHC) with a certain thickness in the North China Plain may be used as an embankment’s bearing layer. However, the mechanical responses of pavements with NHC are not fully understood under cyclic loading. To solve this problem, an accelerated laboratory loading test on the pavements model was conducted to estimate their stress-strain-resilient modulus behaviors. This paper describes the test procedure followed and results obtained on the Soft Soil Layer (SSL) covered with NHC considering vehicle weight, vehicle speed, thickness of NHC, and Compression Modulus Ratio of NHC to SSL (CMR). The results show that vehicle weight is the precondition for the occurrence of strain hardening or strain softening in pavements with NHC. In contrast, vehicle speeds have little effect on the mechanical response of pavements. CMR and the ratio of NHC’s thickness to embankment height are the two important factors to control the plastic deformation of pavements with NHC. The accumulated responses of pavements with NHC can be described by the shakedown approach. It is desirable to consider the direct usage of NHC as a bearing layer without any foundation treatment when CMR is greater than 3.37 and the ratio of NHC’s thickness to embankment height is higher than 2. The magnitude of NHC’s load spreading effect plays an important role in the acceleration or retardation of stress dissipation in SSL layer at different stress states, which may cause the enhancement of strain hardening or strain softening effect in SSL layer.

Keywords

• Accelerated laboratory loading test
• Natural hard crust
• Cumulative vertical plastic strain
• Resilient modulus
• Cyclic loading
• Shakedown