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L-1 Appendix L. Rigid Pavement Structure Model Subroutine The subgrade subroutine will produce subgrade modulus that is both stress and moisture dependent. The base course subroutine will produce a modulus that is anisotropic stress and moisture dependent. It will also calculate the shear strength of the base course on its interface with the bottom of the concrete surface layer. The outputs from subgrade and base course subroutines can be fed into the subroutine for pavements structure model to determine the equivalent thickness of concrete and base course. The pavement structure subroutine outputs the models including: ï· Degree of bonding model. ï· Slab-base equivalent thickness model. The interface shear bonding, , is the ratio of in-situ shear stress in the base course on the slab-base interface and the shear stress in the base layer on the interface when full shear is transferred. The formulation of the degree of bonding is given: (L.1) where is the degree of bonding; is the shear stress in the base course on the slab-base interface; and is the shear stress in the base layer on the interface when full shear is transferred. Table L.1 presents the inputs to the degree of bonding model. Table L.1. Input Variables into Degree of Bonding Model. Input variables Description Unit Moduli Layer Moduli (slab and base) psi thickness layer thickness (slab and base) in PRatio layer Poissonâs Ratio (slab and base) load applied load lb saturated volumetric water content % OMC Optimum moisture content % PI plasticity index Gs specific gravity b width of slab in The equivalent thickness is calculated using the moment of inertia of the transformed section. The transformed section that consists of concrete and base is converted into an equivalent cross section composed of only concrete. The thickness of the equivalent section is estimated by: 12 (L.2)
L-2 where is the slab-base equivalent thickness; and b is the width of slab. is the moment of inertia of the transformed pavement section. Table L.2 presents the inputs to the equivalent thickness model. Table L.2. Input Variables into Equivalent Thickness Model. Input variables Description Unit Moduli Layer Moduli (slab and base) psi thickness layer thickness (slab and base) in degree of bonding b width of slab in
