Resilient modulus of unsaturated silty sand subgrade

Farhad Salour

In flexible pavement structures, moduli of unbound granular layer materials and subgrade soils play an important role in the overall performance of the pavement system. The mechanical behaviour of the unbound layers is conventionally studied by conducting repeated load triaxial (RLT) tests in which the material is characterized using the total stress approach. However, most of the unbound layer materials in pavement structures are often in partially saturated states and even experience short and long term variation in the degree of saturation conditions. Therefore, a more realistic approach in assessment of the mechanical behaviour of the unbound layer materials is to take into account the partially saturated conditions by incorporating pore-suctions (i.e., matric suction) in the material behaviour models. In unsaturated soil mechanic, matric suction is widely used to describe the moisture retention characteristics of the soils. Different approaches have been proposed to use the principles of unsaturated soil mechanic and incorporate the effect of pore-suctions into the resilient modulus modelling. This paper intends to summarize some of the proposed models. Additionally it presents an experimental resilient modulus study- on two silty sand subgrade soils using suction-controlled RLT tests. It further investigates the capability of the different models in capturing the resilient modulus behaviour of the unbound subgrade soils and their variation due to seasonal changes in the pore-suctions (moisture content).

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