Laboratory Report #5

Makeshift Permeameter for Soil Permeability Testing

Abstract

Permeability, or the capacity to transmit fluid, is an important soil property that greatly affects
seepage, stability of slopes and retaining structures, and settlement of soil under a given
loading. Hydraulic conductivity (k), a measure of soil permeability, is determined in the
laboratory using a permeameter. A makeshift permeameter is constructed based on given
standards and it was tested using the constant-head method. A coarse-grained soil sample is
subjected to a constant head of water and the flow is measured. The average value of k for three
trials is 0.117491586 cm/s.

Submitted by: Annamarie San Diego

Group Mates:

Francis Bernales

Michael Lopez

Raniel Mangco

Charles Taran

Date Submitted: December 6, 2016

I. Objectives
Design and implement a makeshift permeameter.
Determine the hydraulic conductivity of a soil sample using the permeameter.
Interpret the test results.

II. Theoretical Background

Figure 1. Constant-Head Test Apparatus

Constant-head test is a standard laboratory test for hydraulic conductivity determination. It is

used primarily for coarse-grained soils such as sands and gravels under laminar flow
conditions. A typical arrangement for the test is shown in Figure 1. In the setup, the water
supply at the inlet section is adjusted such that the there is a constant head of water to each end
of the soil. After establishing constant discharge, water is collected in a graduated flask for a
known duration. The hydraulic conductivity or coefficient of permeability describes the ability
of water to flow through the soil specimen.

Knowing the cross-sectional area of the soil specimen A, height of the soil sample column L,
constant pressure difference h, volume of water collected Q, and the time interval t, the
hydraulic conductivity of the sample is given by:

= (1)
 Figure 2. Standard Permeameter Cell
Source: Lab Permeability - Humboldt Mfg. Co. Website

Standard permeameter sets include a permeameter cell, manometer tubes, valves, perforated
screens or porous stones, and tubing for connecting the water supply and manometer tubes. In
Figure 2, a constant head permeameter cell that complies with ASTM D2434 has mesh screens
to prevent migration of material through the valves and tubes. The acrylic chamber permits
specimen viewing. The cell is also equipped with a loading piston that can be used to apply
constant axial stress during testing. Manometer tubes (not seen in the figure) are used in
combination with the cell to measure pressure difference.

III. Methodology

Figure 4. Makeshift Permeameter Design

 Figure 5. Makeshift Permeameter Actual Set-up

Figure 6. Experiment Proper

The design of the makeshift parameter is illustrated in Figure 4. A plastic pitcher with diameter
105 mm is used as the permeameter tank. The clear plastic allows for specimen viewing during
testing. Plastic tubes were used as a substitute to the manometer tubes and for the outflow drain.
The two manometer tubes are taped to a piece of plywood which serves as a manometer board.
The saturated soil specimen is to be placed in between two circular sponges which act as the
porous layers. Epoxy was used to prevent leakage in the manometer tubes. The actual set-up
of the makeshift permeameter is shown in Figure 5.

To validate the permeameter, a sample of coarse-grained soil was first obtained. It was placed
inside the permeameter tank in between the porous layers. The length of the soil specimen is
67 mm. The water supply into the permeameter tank was turned on, and after waiting for the
water to reach the bottom of the sample, constant inflow and outflow was established. It is also
ensured that the head is constant throughout the test. Outflow water from the permeameter was
collected using a small beaker, recording the time interval to fill a certain volume. Lastly, the
pressure difference h was measured by taking the difference in reading of the two manometer
tubes.

IV. Results and Discussion

The results of the four trials are tabulated below. The value of hydraulic conductivity is
calculated using Equation 1.

Trial Volume Time(s) Q (m3/s) Head (mm) L K (cm/s)

(mL)
1 60 9.04 6.63717E-06 42 0.067 0.122276
2 60 9.01 6.65927E-06 45 0.067 0.114504
3 60 8.84 6.78733E-06 43 0.067 0.122134
4 60 9.29 6.45856E-06 45 0.067 0.111053
AVE: 0.117492
Table 1. Experimental Results

Below is a sample calculation of k for the first trial.

(0.00006 3 )(0.067 )
= = = 0.001222756 /
(0.008659 2 )(0.043)(9.04 )

Averaging the values of K, the soil sample was found to have a hydraulic conductivity of
0.122276 cm/s. Table 2 shows typical values of hydraulic conductivity for different soil types.
 Table 2. Typical Values of Hydraulic Conductivity of Saturated Soils
Source: Principles of geotechnical engineering (Das, 2010)

From the table, the soil is a coarse sand, which is confirmed by the soil classification obtained
in a previous experiment (soil group SP). A high value of hydraulic conductivity is indicative
that the soil is highly permeable. The soil sample is more permeable than fine sands and fine-
grained soils, but is less permeable than gravel. Also, the soil being classified as poorly-graded
influences its permeability. Poor gradation means more voids in the soil particles, therefore
water is more likely to pass through.

V. Conclusion and Recommendations

Using a makeshift permeameter, the hydraulic conductivity of a coarse-grained soil sample was
determined to be 0.117491586 cm/s. This falls under the typical value of hydraulic conductivity
for a coarse sand. However, there is no way to validate these experimental results since a
standard permeameter is not available. Possible sources of error are mostly due to design
limitations of the constructed permeameter, where some standard dimensions are not followed.
It is recommended to perform more trials, using a different set of soil specimen for each. For
more accurate determination of hydraulic conductivity, it is still better to use a permeameter
that follows ASTM standards. The main purpose of this experiment is to exercise the
application of theory to devise a permeameter using available materials and to validate and
interpret the results obtained.

VI. References

ASTM D2434 Standard Test Method for Permeability of Granular Soils (Constant Head)

Das, B. (2010). Principles of geotechnical engineering, 7th edition, Cengage Learning.