# CE2304 Geotechnics – Soil Mechanics Re-sit Coursework (2013/14)

Q1. A cofferdam is constructed to create a dry work environment for

construction of a hydraulic structure. The cross section through the cofferdam

with the length of 40m is shown in the figure Q.1 below. Permeability of the

soil in horizontal and vertical directions is 5 10

⁄ .

a) Draw the flow net for the section of the cofferdam presented in the

figure below [20% of mark]

b) Determine the rate of seepage into the cofferdam [15% of mark]

c) What will be the quantity of water seeped through into the whole

cofferdam in one year’s time? [15% of mark]

Figure Q.1

Q2. A section of an 87m long dam (Figure Q.2.a) and its corresponding flow

net (Figure Q.2.b) are shown below. The hydraulic conductivity value for both

directions for the top soil layer is 3 10

m sec ⁄ and for the bottom soil layer

is 5 10

m sec ⁄ .

Figure Q.2.a

Figure Q.2.b

a) Calculate the scale transformation factor that is used to create the flow

net (Figure Q.2.b) [20% of mark]

b) What is the quantity of seepage per second per unit length of the dam?

[15% of mark]

c) What will be the quantity of water seeping through the whole dam in 5

years? [15% of mark]