The GI values from both graphs are found to be 4.4 and 1.7. So, the GI = 4.4 + 1.7 = 6.1 ≈ 6

\(T=\sqrt{\left(\frac{3×4100×1.5×0.7}{2π×100×0.25}\right)^2-15^2}=80.84 cm\).

Thickness of surface and base = 50 – 20 = 30 cm

Explanation: The group index value is based on the soil type and its physical properties. A higher value of the group index suggests that the soil is of low quality and hence the subgrade will be weak.

Explanation: The subgrade soil is considered as a homogeneous elastic single layer. Boussinesq’s theory can be applied to the soil. in the triaxial method of design, the displacement equation by Boussinesq is made use of.

Explanation: The traffic volume is considered, so CVPD i.e. commercial vehicles per day is taken into account. AADT is the annual average daily traffic and it is considered in the R-value method. For light traffic, the number of commercial vehicles per day must be < 50.

Explanation: The Boussinesq’s deflection equation is given by \(Δ=\frac{3pa^2}{2E(a^2+z^2)^{1∕2}}\) . In this equation, the term z represents depth at which deflection is to be found out. So, the terms in the equation are rearranged and the equation for z is formulated. By assuming that the pavement is incompressible, z can be taken as the thickness of the pavement.

GI =0.2×10+0.005×10×0+0.01×30×0=2

Explanation: There are two methods to find the group index of soil. It can be done either by using the group index charts or by using the equation. There are two charts and the sum of GI from both charts is taken as the final GI.

Explanation: In order to find the values of modulus of elasticity of various materials, a lateral pressure of 1.4 kg/cm2 is applied on the soil subgrade. The value has been arbitrarily assumed by the Kansas State Highway Department, USA as the lateral confinement on their pavement layers.