Significance of bearing capacity of clayey subgrade in flexible pavement design

Clays as subgrades pose serious problems to flexible pavements built over them as they retain moisture for a longer period and possess low strength. Excessive settlements along the wheel tracks on pavement surface and bearing capacity failures in the subgrade soil are often observed in the flexible pavements constructed over such subgrades. So, the present status of flexible pavements in clayey subgrades necessitates investigation into the design procedure. The present paper is intended to assess the adequacy of flexible pavement design thickness based on CBR method against possible risk of shear failure in subgrade soil. A design methodology for flexible pavements based on safe bearing capacity (SBC) of subgrade soil has been presented for evaluating the safety of pavements against shear failure risk. The pavement thickness designs have been carried out in clays of different compressibility from CBR and proposed SBC methods. Two case studies have also been presented wherein shear failure of subgrade has been noticed. Detailed discussion has been made and conclusions have been drawn for efficient design of flexible pavements.