Pavement Design for Carriageway Construction

[axle/vehicle]= 3.16.5 Modulus of Subgrade ReactionIn the design analysis, it is assumed that the reactive pressure provided by thesub-base/subgrade material under a concrete slab is proportional to the deformationbelow the point of loading. The ratio is known as the ‘modulus of subgrade reaction’or ‘k-value’.By using Table 7, the k-value can be estimated from the elastic modulus of thesubgrade, the thickness and modulus of elasticity of the sub-base, in which the elasticmodulus of subgrade should be assessed on-site wherever possible.Table 7 – Modulus of Subgrade Reaction (k) [in N/mm 3 or MPa/mm]E subgradeThickness of Granular Sub-base(MPa) 150 mm 225 mm 300 mm50 0.045 0.050 0.060100 0.060 0.075 0.090150 0.075 0.090 0.110200 0.085 0.105 0.125250 0.095 0.115 0.140300 0.100 0.125 0.1506.6 Properties of ConcreteGrade 40/20 concrete is specified for the construction of rigid pavements in HongKong. The following material properties are adopted in the pavement analysis fordeveloping Design Charts 7 to 9.Modulus of rupture = 5.25 MPaModulus of elasticity = 33,000 MPaPoisson’s ratio = 0.15Temperature differential = 2.7 o C within typical slab thickness6.7 Structural DesignFor structural design of rigid pavements, Design Charts 7 to 9 shall be followed forslab length of 4m, 5m, and greater than or equal to 6m respectively.RD/GN/042 Pavement Design for Carriageway Construction Page 23 of 42