Civil Engineering Reference
In-Depth Information
Exercise 11.2
A rectangular, flexible foundation has dimensions L
=
4 m and B
=
2 m and is loaded
with a uniform pressure of 400 kPa. The foundation sits on a layer of deep clay,
E
=
10 MPa. Determine the immediate settlement values at its centre and at the
central points of its edges.
Answer
At centre
=
92 mm
At centre of long edge
=
67 mm
At centre of short edge
=
58 mm
Exercise 11.3
A rectangular foundation, 10
×
2 m
2
, is to carry a total uniform pressure of 400 kPa
and is to be founded at a depth of 1 m below the surface of a saturated sand of
considerable thickness. The bulk unit weight of the sand is 18 kN/m
3
and standard
penetration tests carried out below the water table indicate that the deposit has an
average N value of 15.
If the water table occurs at the proposed foundation depth, determine a value
for the settlement of the centre of the foundation. (Use De Beer and Martens'
method.)
Answer
50 mm
Exercise 11.4
A saturated sample of a normally consolidated clay gave the following results when
tested in a consolidation apparatus (each loading increment was applied for 24
hours).
Consolidation
pressure (kPa)
Thickness of
sample (mm)
0
17.32
53.65
16.84
107.3
16.48
214.6
16.18
429.2
15.85
0
16.51
After the sample had been allowed to expand for 24 hours it was found to have a
water content of 30.2%. The particle specific gravity of the soil was 2.65.
(i) Plot the void ratio to effective pressure.
(ii) Plot the void ratio to log effective pressure and hence determine a value for the
compression index of the soil.
(iii) A 6.1 m layer of the soil is subjected to an existing effective over burden pres-
sure at its centre of 107.3 kPa, and a foundation load will increase the pressure
at the centre of the layer by 80.5 kPa.
