Find out the rate that water can be transported through various soil
samples that are fully saturated. When under a constant flow, we want to find the velocity of
flow and coefficient of permeability.
Introduction:
Water is a very low viscous substance, meaning that its properties allow it to flow very freely
through different materials. Soil permeability is the ease at which a substance like water can pass
through soil, which means that during rainfall or irrigation, water moves easily through high
permeability soil, and slowly through low permeability soil. This is important because it gives
engineers an idea as to how stable a foundation is, as well as the seepage rate through
embankments and dams. There are a few factors that can decide how permeable a type of
soil/rock is, such as particle size, the impurities in the water, and the degree of saturation of the
soil.
Whenever the soil is fully saturated, then a constant input of water will lead to a constant output
of water. The ability for the soil to transmit water under saturated or fully saturated conditions is
known as the hydraulic conductivity. For this lab, we will use the constant head permeability test
in order to find the flow and coefficient of permeability (K) of the soil.
Apparatus:
● Permeameter
● Tamper
● Balance
● Scoop
● 1000 mL Graduated cylinders
● Stopwatch
● Thermometer
● Filter paper
4
Procedure:
- Determine the mass of the plastic specimen tube, the porous stones, the spring, and the two
rubber stoppers, M1 (see line 3 of Table 13–4). - Slip the bottom porous stone into the specimen tube and then fix the bottom rubber stopper to
the specimen tube. - Collect oven-dry sand in a container. Using a spoon, pour the sand into the specimen tube in
small layers, and compact it by vibration and/or other compacting means. (Note: By changing the
degree of compaction, a number of test specimens having different void ratios can be prepared.) - When the length of the specimen tube is about two-thirds the length of the tube, slip the top
porous stone into the tube to rest firmly on the specimen. - Place a spring on the top porous stone, if necessary.
- Fix a rubber stopper to the top of the specimen tube. (Note: The spring in the assembled
position will not allow any expansion of the specimen volume, and thus the void ratio, during the
test.) - Determine the mass of the assembly, M2 (Step 6) (see line 4 of Table 13–4).
- Measure the length L and the diameter D of the compacted specimen in the tube (see top of
Table 13–4 and lines 5 and 6 of Table 13–5). - Assemble the permeameter near a sink, as shown in Fig. 13–2(a).
- Run water into the top of the large funnel fixed to the stand through a plastic tube from the
water inlet. The water will flow through the specimen to the constant-head chamber. After some
time the water will flow into the sink through the outlet in the constant-head chamber. (Note:
Make sure that water does not leak from the specimen tube.) - Adjust the supply of water to the funnel so that the water level in the funnel remains constant.
At the same time, allow the flow to continue for about 10 minutes in order to saturate the
specimen. (Note: Some air bubbles may appear in the plastic tube connecting the funnel to the
specimen tube. Remove the air bubbles.) - After a steady flow is established (that is, once the head difference h (see line 4 of Table
13–5) becomes constant), collect the water Q (see line 1 of Table 13–5) flowing out of the
constant-head chamber in a graduated cylinder. Record the collection time t with a stopwatch
(see Fig. 13–2(b)). - Repeat Step 12 three times. Keep the collection time the same and determine Q.Then find the
average value of Q. - Change the head difference h and repeat Steps 11, 12, and 13 about three times.
- Record the temperature T (see line 3 of Table 13–5) of the water to the nearest degree.
(Note: This value is sufficiently accurate for this type of test.)
5
Results/ Data Sheet:
Sample Diameter = 75mm Sample area (A) = 4415.6mm
Distance between top and middle manometers (L) 75mm
Distance between middle and bottom manometers (L) 75mm
Test
No.
Test 1 Test 2
Head level (top manometer), H1
, mm 1411 1324
Head level (middle manometer). H2
, mm 1328 1206
Head level (bottom manometer, H3) mm 1252 1096
Volume of flow (Q), ml 92 90
Volume of flow (Q), mm3 92000 90000
Time, s 43 30
Temperature, °C 25 25
Coefficient of permeability (k), mm/s 0.458 0.447
Coefficient of permeability (k), m/s 0.00046 0.00045
k20
, m/s 0.00042 0.00041
k1 0.4378 0.4318
k2 0.4782 0.4632
k3 0.4571 0.4470
AVG K 0.4577 0.4473
T,°C kt T,°C kt
0 1.779 25 0.906
4 1.555 30 0.808
10 1.299 40 0.67
15 1.133 50 0.55
20 1 60 0.468
6
Mass of permeability cell (M0) = 8.7 g
Initial Dry Mass of Soil + cell (M1) = 10.8 g
Mass of Dry Soil Specimen (M1-M0) = 2.1 g
Length of Soil Specimen, L = 75 cm
Diameter of the Soil Specimen (Permeameter), D = 1.5 cm
Final Mass of Soil + Cell (M2) = 12.4 g
Mass of Soil Specimen (M2-M0) =3.7 g
Diameter of soil=0.15 mm or 1.5 cm
Volume of Soil Specimen (V) =cm3 =1.77 cm3
Dry Density of Soil (ρ) = 2.66×1000= 2660 kg/m3 or 2.66 g/cm3
Discussion: - As temperature increases, permeability will increase. It is due to a decrease in viscosity with
an increase in temperature. - Round shape particles are more permeable than angular-shaped particles as the specific area of
angular-shaped particles is more than round-shaped particles. The permeability of smaller
particles is low as the space between particles is less, causing a low porosity. Thus, water moves
slowly through the ground. The capillary action of smaller particles is higher.
7
3.Greater the void ratio, the higher will be the permeability. However, it is not for all types of
soils. For example, clay has a higher void ratio as compared to other soils but its permeability is
low. - The calculations show that the degree of permeability of soil is medium.
Conclusion:
The coefficient of permeability of this soil was attained through the constant head permeability
test. At an average of .4577, this soil can be identified as a fine sand classifying it as a high
permeable soil. The higher the temperature of the water, the easier the water is able to flow
through the soil.
8
References:
“Lab Experiment video manual: Soil Constant Head Permeability”
Video: https://youtu.be/TaPjIvCsfFI