Question $41\mathrm{.}5\%.$ In a deposit of fine sand the water table is $3\mathrm{.}5m$ below the surface but sand to a beight of $1\mathrm{.}0m$ above the water table is saturated by capillary water: above this height the and may be assumed to be dry. The saturated and dry unit weights, respectively, are $20k\frac{N}{m^3}$ and $16kNm{m}^3.$ Calculate the effective vertical stress in the sand $8m$ below the surface.