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1.0 OBJECTIVE

To determine permeability of sands and gravels containing little or no silt

2.0 LEARNING OUTCOME

at the end of this experiment, students are able to

describe the procedure to determine the coefficient of permeability of sands and

gravels based on on ASTM D2434

identify the relationship between the permeability and pore size of the coarse

grained soils.

Measure the coefficient of permeability of sands and gravels containing little or no

silt

3.0 THEORY

The most common permeability cell (permeameter) is 75mm in diameter and is intended

for sands containing particles up to about 5mm. A larger cell, 114mm, can be used for

testing sands containing particles up to about 10mm, i.e. medium gravel size. As a general

rule the ratio of the cell diameter to the diameter of the largest size of particle in

significant quantity should be at least 12.

The constant head permeability cell is intended for testing disturbed granular soils which

are recompacted into the cell, either by using a specified compactive effort, or to achieve

a certain dry density, i.e. void ratio.

In the constant head test, water is made to flow through a column of soil under the

application of a pressure difference which remains constant, i.e. under a constant head.

The amount of water passing through the soil in a known time is measured, and the

permeability of the sample is calculated by using Equation (1).

If the connections to the cell are arranged so that water flows upwards through the

sample, the critical hydraulic gradient can be determined after measuring the steady state

permeability, and the effects of instability (boiling and piping) can be observed. It is

important that use only air-free water, and measures for preventing air bubbling out of

solution during these tests is very crucial.

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(Eqn 1)

Where : q = rate of flow

A = area of sample

I = hydraulic gradient

h1 h2 = head difference between 2 reference points

L = distance between 2 references points

4.0 TEST EQUIPMENTS

1. Constant head permeability cells, fitted with loading piston, perforated plates, flow

tube connections, piezometer nipples and connections, air bleed valve, sealing rings.

Figure 1shows permeameter cells that commonly used in laboratory testing

Figure 1 : Permeameter cells for constant head test: (a) 75mm, (b) 114 mm (courtesy

of ELE International, 2007)

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5.0 PROCEDURES

1. Prepare permeameter cell,

a. Remove the top plate assembly from the cell

b. Measure the following dimensions :

i. Mean internal diameter (D mm)

ii. Distance between centres of each set of manometer connection points

along the axis of the cell (L mm)

iii. Overall approximate internal length of cell (H1 mm)

c. Calculate the following based on measured dimensions :

i. Area of cross- section of sample, A = D2 / 4 mm2

ii. Approximate mass of soil required, to fill the permeameter cell V = AH1 /

1000 g

iii. Approximate mass of soil required, if placed at a density Mg/m3, mass =

AH1/1000g

2. Select sample

a. Air-dry the soil which the test sample is to be taken

b. Sieve the soil sample and any particles larger than 5 mm need to be remoed by

sieving

c. The material needs to be reduced by the usual riffling process to produce several

batches of samples each about equal to the mass required to fill the permeameter

cell

3. Prepare sample,

a. The sample may be placed in the permeameter cell by one of three methods :

i. Compacting by rodding

ii. Dry pouring

iii. Pouring through water

4. Assemble cell

a. Place a second porous disc (if one has already been used) and the second wire

gauze disc on top of the soil, followed by about 40 mm thickness of glass balls or

gravel filter material

b. The level of the top surface of the filter should be within the limits required to

accommodate the top plate

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c. Slacken the piston locking collar on the cell top, pull the piston up as far as it will

go, and re-tighten the locking collar

d. Fit the cell top on the cell and tighten it down into place by progressively

tightening the clamping screws

e. Release the piston locking collar and push the piston down until the perforated

plate bears on the filter materials

f. Hold it down firmly while the locking collar is re-tightened

5. Connect up cell

a. Connect the nozzle at the base of the cell to the de-aired water supply, and close

the inlet cock

b. Connect each piezometer point that is to be used to a manometer tube and close

with a pinchcock close to the cell

c. Connect the top outlet of the cell to the vacuum, fitted with a water trap, using

rigid plastic or

d. Close the air bleed screw on the cell top

6. Saturate and de-air sample

7. Connect up for a test

8. Run a test

a. Turn on the supply of de-aired water to the constant head device, which be at alow

level initially,

b. Open water supply valve that connect it to the cell, and the base outlet cock c.

c. Allow water to flow through the sample until the conditions appear to be steady

and the water levels in the manometer tubes remain stationarye

d. Adjust valve on the supply line to the constant head device so that there is a

continuous small overflow; if this is excessive, the de-aired water will be wasted.

e. To start a test run, empty the measuring cylinder and start the timer at the instant

the measuring cylinder is placed under the outlet overflow.

f. Record the clock time at which the first run is started.

g. Read the levels of the water in the manometer tubes (h1, h2,etc) and measure the

water temperature (TC) in the outlet reservoir.

h. When the level in the cylinder reaches a predetermined mark (such as 50ml or

200ml) stop the clock, record the elapsed time to the nearest half second

9. Repeat test

a. Empty the cylinder, and make four to six repeat runs at about 5 minutes intervals

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10. Dismantle cell

11. Calculate the result

12. Report

Figure 2 : general arrangement for costant head permeability test (downward flow)

(courtesy of ELE International,2007)

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6.0 AND CALCULATIONS

Constant Head Permeability test

Location : Geotechnic Laboratory Sample no :

Operator : Date : 14 September 2014

Soil Description : Sand

Method of

preparation :

Sample diameter : 80 mm Sample Length

Sample area, A : 5026 mm2 Sample Volume : 1166 cm

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Sample dry mass : 1925 g Sample dry density : 16.19 kN/m3

S.G. measured/assumed Voids ratio :

Heights above datum : inlet Heights above datum : outlet

Manometer a : mm Manometer b: mm Manometer c : mm

Head difference a to c : 38 mm Distance difference : 90 mm

Flow upwards/downwards : downwards Hydraulic gradients : 0.42

Temperature :

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Reading :

Time from

start

min

Time

interval, t

min

Measured

flow, Q

ml

Rate of flow,

q

=Q/t

ml/min

Remarks

m/s

12.00 PM 0 0 0 0 0

12.02 PM 1 1480 1520.00 1.00 1.200 x 10-5

12.04 PM 1 1480 1520.00 1.00 1.200 x 10-5

12.06 PM 1 1480 1520.00 1.00 1.200 x 10-5

12.08 PM 1 1480 1520.00 1.00 1.200 x 10-5

12.10 PM 1 1480 1520.00 1.00 1.200 x 10-5

12.12 PM 2 3000 1500.00 0.71 1.184 x 10-5

12.15 PM 2 3000 1500.00 0.71 1.184 x 10-5

12.18 PM 2 3000 1500.00 0.71 1.184 x 10-5

12.21 PM 2 3000 1500.00 0.71 1.184 x 10-5

12.24 PM 2 3000 1500.00 0.71 1.184 x 10-5

12.27 PM 3 4480 1493.33 0.58 1.180 x 10-5

12.31 PM 3 4480 1493.33 0.58 1.180 x 10-5

12.36 5 7430 1486.00 0.45 1.175 x 10-5

7.0 DATA ANALYSIS

Sample area,

A = 5026 mm2

(from the lab sheet)

Sample Volume,

V = 1166 mm2 (from the lab sheet)

= 0.42

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Rate flow,

q1 = 1480 ml/min

1520

x

= 2.53 x 10 -5

m3/s

Rate flow,

q2 = 1500 ml/min

1500

x

= 2.5 x 10-5

m3/s

Rate flow,

q3 = 1493.33 ml/min

1493.33

x

= 2.49 x 10-5

m3/s

Rate flow,

q4= 1486 ml/min

1486

x

= 2.48 x 10-5

m3/s

Permeability

K1=

=

= 1.20 x10-5

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Permeability

K2 =

= 1.184 x 10-5

Permeability,

K3 =

=1.18 x 10-5

m/s

Permeability,

K4 =

= 1.175 x 10-5

m/s

8.0 QUESTIONS

1. Determine the coefficient of permeability for the given sample of soil

K=

k = ( ) ( )

= 1.177 x 10-5

m/s

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2. Give a conclusion for this test

From the experiment, we can know that the objective of the experiment is to

determine the permeability of sands and gravels containing little or no silt. From the

experiment that have done, we can know that the objective for this experiment was

achieved. This is because the value of permeability of sands is k = 1.177 x 10-5

m/s.

From the table of value permeability (from discussion), our results test we located in

categorized as fine sands. It means that the soil are using through this experiment is

fine sands.

9.0 DISCUSSION

The value of the k (permeability) that we get is 1.177 x 10-5

m/s. This value we get by

using the formula

K=

Before that, we find the value Ai first and after that we get the value of q. So, the

permeability of this sample is moderate. This is because the porosity of sand and

gravel is high or moderate where by water can flows through the soil with less

resistance. It can drain water easily but hardly can retain any water. The greater pore

size of soil is more permeability then the soil with smaller pore size. From value of k,

we can classify the type of soil that we use is silty sands or silty clays and this types

of soil is not suitable for drainage system.

Table 1 shows the range of average values for k for various soil and also indicates

potential

drainage.

Soil Type K (m/s) Potential

Fine Gravel 100 1 Very good drainage

Medium and Coarse Sands 1 10-1 Very good drainage

Fine Sands 10-1 10-2 Very good drainage

Silty sands 10-2 10-3 Good drainage

Silt and Silty Sands 10-3 10-5 Good drainage

Silty sands, silty clays 10-5 10-7 Poor drainage

Clays 10-7 10-9 Practically impervious

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The coefficient of permeability may be defined as the flow velocity produced by

ahydraulic gradient of unity. The value of k is use as a measure of the resistance to flow

offered bythe soil, and it is affected by several factors:

a. The porosity of the soil.

b. The particle-size distribution.

c. The shape and orientation of soil particles.

d. The degree of saturation/presence of air.

e. The type of cation and thickness of adsorbed layers associated with clay mineral.

f. The viscosity of the soil water, which varies with temperature.

In our measurement, there has some error occurred. First, instrumental error occurred

because of the wrong adjustment of the devices when the observation was made. On the other

hand, the human factors also give the effects to the traverse work which is due to the inability

of the observer to give a correct reading of a measurement. There has many mistakes

occurred from the carelessness of the observer. The carelessness and mistakes are including

of wrong reading measurement, inexperience of controlling the instrument and some of

mistakes in calculation works..

However, we managed to overcome this problem with a few precautions and steps in

order to minimize the errors from affected our result. For the instrumental factor, we make

carefully set up the constant head test instruments until it comes to a perfect condition. For

the carelessness of the observer, we overcome it by placing the eyes perpendicularly to the

reading so we can get a correct readings. Furthermore, the error caused by human factors, we

solving it by carefully in all actions of collecting the data including the data readings, data

recording and calculation works.

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10.0 CONCLUSION

As a conclusion, we get the time is found to be constant at volume of water. The time we get

is faster. This is because the permeability of the gravel soil absorbs the water is low. This

gravel soil has a large molecular space. Therefore, the water diffusion rate is low. It appears

to be a function of three factors for a constant paste amount and character: effective air void

content, effective void size and drain down. From the coefficient of permeability for the

given sample of soil value, we can say that the rate of flow the sample has get the higher

value.

11.0 REFERENCES

1. http://www.studymode.com/essays/Constant-Head-Permeability-Test-1151824.html

2. http://www.slideshare.net/xakikazmi/constant-head

3. Geotechnic Laboratory Report, Department of Civil Engineering UTHM