Which of the following is the correct form of Boussinesq’s Equation used to compute vertical stress $$(\sigma_z)$$ at a particular point located at a depth z and at a horizontal distance r from the vertical axis through the point load Q acting on the surface.

A

$$\sigma = \frac{3Q}{2 \pi z^2\left[1 + \left(\frac{r}{z}^2\right)\right]^{\frac{5}{2}}}$$

B

$$\sigma_z = \frac{2Q}{3 \pi z^2\left[1 + \left(\frac{r}{z}^2\right)\right]^{\frac{5}{2}}}$$

C

$$\sigma_z = \frac{3Q}{2 \pi z^2\left[1 + \left(\frac{r}{z}^2\right)\right]^{\frac{3}{2}}}$$

D

$$\sigma_z = \frac{2Q}{3 \pi z^2\left[1 + \left(\frac{r}{z}^2\right)\right]^{\frac{3}{2}}}$$