Subgrade Contact Pressures under Rigid Pavements

Subgrade contact pressures under rigid pavements were analyzed using the finite element method for concrete slabs on liquid and elastic subgrades. It was found that when the maximum bending stress in the slab is made in agreement in the two analyses, the deflections and subgrade contact pressures are much greater for elastic than for liquid subgrades. Although initial bending stresses in the concrete slab are well below the concrete strengths, excessive subgrade pressures undoubtedly cause large permanent deformations in the subgrade soil, possibly increasing the stresses in the concrete slab rapidly and eventually leading to early failure of the concrete pavement. The computation of large subgrade pressures at slab edges only in pavements with weak subgrade soil supports the Corps of Engineers design practice of reduction of pavement thickness for pavements with high subgrade k values, although bending stresses in the concrete slab are only slightly affected by variations in k values. Once initial cracking in the concrete slab has occurred, the large contact pressures at slab edges computed for concrete pavements on weak subgrade must have escalated multiple cracking in the concrete slab. The subgrade contact pressures under rigid pavements should be experimentally measured to verify the results computed by the finite element method.