Question No$.4$

$[25$ Marks $]$

a$)$ What determines the Flow of water through a permeable medium like soils? What other characteristics of soils affect the rate of flow?

$[4]$

b$)$ In a soil test, it took $16\mathrm{.}0$ min for $1508$ cm $3$ of water to flow through a Sand sample, the cross$-$sectional area of which was $50\mathrm{.}3$ cm $2.$ The void ratio of the sample was $0\mathrm{.}68.$

Determine

The velocity of water through the soil

$[2]$

The actual $($interstitial$)$ velocity

$[3]$

c$)$ Permeability determined in a laboratory may not be truly indicative of the insitu permeability; give four possible reasons for this disparity

$[4]$

Fig. $3$ Weir

Use the diagram in Fig. $3$ above to carry out the following;

a$)$ Reconstruct the diagram and draw a flow net. Explain the important features of the flow net.

$[8]$

b$)$ Use the flow net constructed above to calculate the total rate of seepage per unit width of weir through the permeable layer given $Kx=Ky=8\mathrm{.}15{10}^{-3}c\frac{m}{s}.$

$[4]$