Constent Head Permeability Test

CC303 : Geotechnic Engineering

EXPERIMENT 8 CONSTANT HEAD PERMEABILITY TEST PUAN SITI MARLINNA CHU BINTI MOHD RIZAL CHU NAME IDA RAHAYU BINTI AMRAN MOHD ADHAM BIN MOHD ARIF NURUL ELYANIE SYAFIKA BINTI MOHAMED ZURREEN ATIQA BINTI JAZULI AYU KARLINA BINTI SHARIPUDIN

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CC303 : Geotechnic Engineering

OBJECTIVE 1. 2. 3. 4. 5.

To determine the coefficient of permeability of a soil using constant head method. Solving problems involving yield of water bearing strata. Seepage through earthen dams. Stability of earthen dams. Embankments of canal bank affected.

APPARATUS 2 | Page

CC303 : Geotechnic Engineering

1.

CONSTANT HEAD PERMEAMETER

2.

GRADUATED FLASK

3.

BALANCE

4.

ASSEMBLED CONSTANT HEAD PERMEAMETER

5.

STOP WATCH

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CC303 : Geotechnic Engineering

THEORY The constant head permeability test involves flow of water through a column of cylindrical soil sample under the constant pressure difference. The test is carried out in the permeability cell, or permeameter, which can vary in size depending on the grain size of the tested material. The soil sample has a cylindrical form with its diameter being large enough in order to be representative of the tested soil. As a rule of thumb, the ratio of the cell diameter to the largest grain size diameter should be higher than 12 (Head 1982). The usual size of the cell often used for testing common sands is 75 mm diamater and 260 mm height between perforated plates. The testing apparatus is equipped with a adjustable constant head reservoir and an outlet reservoir which allows maintaining a constant head during the test. Water used for testing is de-aired water at constant temperature. The permeability cell is also equipped with a loading piston that can be used to apply constant axial stress to the sample during the test. Before starting the flow measurements, however, the soil sample is saturated. During the test, the amount of water flowing through the soil column is measured for given time intervals. Knowing the height of the soil sample column L, the sample cross section A, and the constant pressure difference Δh, the volume of passing water Q, and the time interval ΔT, one can calculate the permeability of the sample as K=QL / (A.Δh.Δt)

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CC303 : Geotechnic Engineering

PROCEDURE UNDISTURBED SOIL SAMPLE 1) Note down the sample number, bore hole number and its depth at which the sample was taken. 2) Remove the protective cover (paraffin wax) from the sampling tube. 3) Place the sampling tube in the sample extraction frame, and push the plunger to get a cylindrical form 4) Sample not longer than 35 mm in diameter and having height equal to that of mould. 5) The specimen shall be placed centrally over the porous disc to the drainage base. 6) The angular space shall be filled with an impervious material such as cement slurry or wax, to provide 7) The sealing between the soil specimen and the mould against leakage from the sides. 8) The drainage cap shall then be fixed over the top of the mould. 9) Now the specimen is ready for the test.

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CC303 : Geotechnic Engineering

DISTURBED SOIL SAMPLE 1) A 2.5 kg sample shall be taken from a thoroughly mixed air dried or oven dried material. 2) The initial moisture content of the 2.5 kg sample shall be determined. Then the soil shall be placed in the air tight container. 3) Add required quantity of water to get the desired moisture content. 4) Mix the soil thoroughly. 5) Weigh the empty permeametermould. 6) After greasing the inside slightly, clamp it between the compaction base plate and extension collar. 7) Place the assembly on a solid base and fill it with sample and compact it. 8) After completion of a compaction the collar and excess soil are removed. 9) Find the weight of mould with sample. 10) Place the mould with sample in the permeameter, with drainage base and cap having discs that are properly saturated.

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CC303 : Geotechnic Engineering

TEST PROCEDURE 1) For the constant head arrangement, the specimen shall be connected through the top inlet to theconstant head reservoir. 2) Open the bottom outlet. 3) Establish steady flow of water. 4) The quantity of flow for a convenient time interval may be collected. 5) Repeat three times for the same interval

RESULT soil description : sand and gravel method of preparation : compaction Sample diameter : 75.35mm 7 | Page

Sample length : 93.6mm

CC303 : Geotechnic Engineering Sample area, A : 4459.194mm2 Sample dry mass : 1230g

Manometer a : 595mm Manometer b : 570mm

READING First attempt Time from start (min)

Time interval, t (min)

Measured flow, Q (ml)

Remarks ¿^ VL k= ¿

8.15 am

0.45

500

0.933

9.00 am

0.45

1000

1.866

9.45 am

0.43

1500

2.929

10.30 am

0.45

2000

3.732

Time from start (min)

Time interval, t (min)

Measured flow, Q (ml)

Remarks ¿^ k = VL ¿

8.30 am

0.35

500

1.200

9.05 am

0.38

1000

2.210

9.44 am

0.39

1500

3.230

10.54 am

0.38

2000

4.419

Second attempt

CALCULATION

Permeability, k =

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¿^ VL ¿

CC303 : Geotechnic Engineering

First attempt i.

K= 500(93.6) / 25(4459.194)(0.45) =0.933

ii.

K= 1000(93.6) / 25(4459.194)(0.45) = 1.866

iii.

K= 1500(93.6) / 25(4459.194)(0.43) = 2.929

iv.

K= 2000(93.6) / 25(4459.194)(0.45) = 3.732

Second attempt i.

K= 500(93.6) / 25(4459.194)(0.35) = 1.200

ii.

K= 1000(93.6) / 25(4459.194)(0.38) = 2.210

iii.

K= 1500(93.6) / 25(4459.194)(0.39) =3.230

iv.

K= 2000(93.6) / 25(4459.194)(0.38) = 4.419

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CC303 : Geotechnic Engineering

DISCUSSION The value of the k (permeability) at the first attempt that we get is 0.933, 1.866, 2.929 and 3.732. For the second attempt we get 1.200, 2.210, 3.230 and 4.419. This value we get by using the formula. 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 gravelis 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.

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CC303 : Geotechnic Engineering

CONCLUSION As a conclusion, we get the time to be constant at volume of water. The time that 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 which is 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 value is higher.

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