Finite Element Based Design of Unreinforced Unpaved Roads Resting on Deformable Marginal Soil Subgrade

Unpaved road comprises around 80 to 85% of global road network, and has to pass over marginalized subgrades in many instances. Traditional design practices of unpaved roads consider the road structure to be in rigid condition with a subgrade layer purely cohesive in nature. The strength characteristics of such subgrade is represented by the undrained cohesion of the subgrade. However, a large portion of Indian unpaved road network rest on marginalized subgrade soil. Under quasi-static vehicular loading condition, it is idealistically assumed that the individual components (aggregate and subgrade) would not undergo failure under the transfer of stress generated by surface loads. However, such design approach results in conservativism that ultimately increases the overall cost of the construction. To overcome these constraints, a finite-element (FE) based study is conducted to model unreinforced unpaved road resting on c-φ soil subjected to a typical combination of axle loads and tire pressures. The study considers the individual failure of the subgrade and aggregate under construction and vehicular load respectively. Step-by-step design philosophy is developed to assess the least shear strength parameters of the individual components required to prevent failure considering coupled stress-deformation effects.