Page 47 - Materials Chemistry, Second Edition

30 Practical Design Calculations for Groundwater and Soil Remediation

TABLE 2.3
Typical Height of Capillary Fringe
Capillary Rise (cm)
Grain Size Pore Radius
Material (mm) a (cm) b Source A a Source B b
Gravel
Coarse … 0.4 … 0.38
Fine 2–5 … 2.5 …
Sand
Very coarse 1–2 … 6.5 …
Coarse 0.5–1 0.05 13.5 3.0
Medium 0.2–0.5 … 24.6 …
Fine 0.1–0.2 0.02 42.8 7.7
Silt
0.05–0.1 0.001 105.5 150
0.02–0.05 … 200 …
Clay … 0.0005 … 300
Source: [5, 6].

Example 2.16: Thickness of Capillary Fringe
A core sample was taken from an impacted unconfined aquifer and ana-
lyzed for pore size distributions. The effective pore radius was determined
to be 5 μm. Estimate the thickness of the capillary fringe of this aquifer.

Solution:
−6
−4
Pore radius = 5 × 10 m = 5 × 10 cm
Using Equation (2.11), we obtain
−4
Capillary rise = (0.153)/(5 × 10 ) = 306 cm = 3.06 m = 10.0 ft

Discussion:
1. Equation (2.11) is an empirical equation. The units for capillary
rise and pore radius in this equation need to be in centimeters.
By looking at the equation, having both units in centimeters does
not seem to match. However, the constant (0.153) has taken care
of the unit conversions. If other units are used, the value of the
constant would be different.
2. The calculated value (306 cm) for the capillary rise is essentially
the same as the value (300 cm) listed in Table 2.3 for clay with
pore radius of 0.005 mm.