29.1.2. Relative stiffness of slab to sub-grade

Try these first

1. 1.

   What is the radius of relative stiffness?

   Hint

   Think of it as a measure of how stiff the slab is compared to what lies underneath it.

2. 2.

   What role does the modulus of elasticity (E) play?

   Hint

   Higher values typically indicate stiffer materials.

3. 3.

   What does the radius of relative stiffness help determine in pavement design?

   • Thickness only
   • Strength of sub-grade
   • Performance of the slab

   Hint

   Think about what helps sustain the slab during load applications.

4. 4.

   True or False: A higher modulus of elasticity indicates a less capable material.

   • True
   • False

   Hint

   Consider how elasticity relates to strength.

5. 5.

   Given a cement slab with a thickness of 25 cm, calculate the radius of relative stiffness if the modulus of elasticity is 3.5 x 10^5 kg/cm2, K is 3 kg/cm3, and µ is 0.2.

   Hint

   Be careful with K and the Poisson’s ratio!

6. 6.

   Critique the design of a slab with low stiffness and identify three possible design changes to improve its performance.

   Hint

   Reflect on what changes typically strengthen structures.