Geotechnical Engineering

DHARM

158 GEOTECHNICAL ENGINEERING

Substituting, hc =

4 T

d

s

γwc

= 36 cm,

since dc for the second soil is double that of the first soil and since hc ∝

1

dc

.

Example 5.20. The figure (Fig. 5.31) shows a tube of different diameter at different sections.
What is the height to which water will rise in this tube? If this tube is dipped in water and
inverted, what is the height to which water will stand? What are the water pressures in the
tube at points X, Y and Z?
Let us denote the top level of each section above the water level as h and the height of
capillary rise based on the size of the tube in that section, as hc.

Using hc (mm) =

30

dc(mm)

,

we can obtain the following as if that section is independently immersed in water :

dc (mm) hc(mm) h(mm) Remarks

2 15 10 Water enters the next section

1 30 20 Water enters the next section

0.75 40 35 Water enters the next section

0.50 60 70 Water does not enter the next section

15 15 mmmm2mmf

x

y

1

mm

10 mm f

10 mm

40

mm

40

mm

15 mm 0.75^60 60 mmmm

mmf

35 mm

5mm 0.2 mmf

Free water level

0.5

mmf

z

Fig. 5.31 Tube with varying section (Example 5.20)

Therefore water enters and stands at 60 mm above free water level.

If the tube is dipped in water and inverted,

hc = 30/dc = 30/0.2 = 150 mm.

Since this is greater than the height of the tube, it will be completely filled.