Geotechnics – Soil Mechanics

Geotechnics – Soil Mechanics
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]

NOTE: