Constant Head

STUDENT CODE OF ETHIC (SCE) DEPARTMENT OF INFRASTRUCTURE AND GEOMATIC ENGINEERING FACULTY OF CIVIL & ENVIRONMENTAL ENGINEERING

I, hereby confess that I have prepared this report on my own effort. I also admit not to receive or give any help during the preparation of this report and pledge that everything mentioned in the report is true.

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FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING

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TEST TITLE: CONSTANT HEAD PERMEABILITY TEST

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1.0 OBJECTIVE TO DETERMINE THE PERMEABILITY OF SANDS AND GRAVELS CONTAINING LITTLE OR NO SILT.

2.0 LEARNING OUTCOME OUTCOME  At the end of this experiment, students are able to: coeffici ent of permeability of sands and gravels based on  Describe the procedure to determine the coefficient BS 1377.  Identify the relationship between permeability and pore size of the coarse grained soils. coefficient of of permeability permeability of sands sands and gravels containing little or or no silt.  Measure the coefficient

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 bubbling out of solution during these tests is very crucial.

Permeab Permeability,k ility,k (m / s)

Where: q = rate of flow,  A = area of sample, sample, i  = hydraulic gradient, =

h2

 h1 L

h1 - h2 = head difference between 2 reference points L = distance between 2 reference points

q 

Ai

 

(1)

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: CONSTANT HEAD PERMEABILITY TEST

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4.0 TEST EQUIPMENTS 1. Constant head permeability permeability cells, fitted with loading piston, perforated perforated plates, flow tube connections, connections, piezometer nipples and connections, air bleed valve, sealing rings. Figure 1 shows permeameter cells that commonly used in laboratory testing.

Figure 1: Permeameter cells for constant head test: (a) 75mm, (b) 114mm (Courtesy of ELE International, 2007)

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: CONSTANT HEAD PERMEABILITY TEST

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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 (H 1 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 = A H1/1000 cm3 iii. Approximate mass of soil required, required, if placed at a density  Mg/m3, mass =  A H1/1000 g 2. Select sample, a. Air-dry the soil which the test sample sample is to be taken. taken. b. Sieve the soil sample and any particles larger than 5 mm need to be removed 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 40mm thickness of glass balls or gravel filter material, b. The level level of the top top surface of the filter should be within the limits required required to accommodate the top plate, c. Slacken the piston locking locking collar on the cell cell top, pull pull the piston 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 material, f. Hold it down down firmly firmly while the locking collar is re-tightened 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 the top outlet outlet of the cell to the vacuum, fitted fitted with a water trap, trap, using rigid rigid plastic or thick-walled rubber tubing d. Close the the air bleed screw on the cell cell top

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: CONSTANT HEAD PERMEABILITY TEST

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6. Saturate and de-air sample 7. Connect up for test 8. Run test a. Turn on the supply of de-aired water to the constant head device, which be at a low level initially, b. Open water water supply valve that connect it to the cell, and the base outlet outlet cock c. Allow water to flow through the sample until the conditions appear to be steady and the water levels in the manometer tubes remain stationary d. Adjust valve on the supply line to the constant head device so that there is a continuous continuous small overflow; if this is excessive, the de-aired water water will be wasted. e. To start a test run, run, empty the measuring cylinder and start the timer at the instant the the measuring cylinder is placed under the outlet overflow. f. Record the clock time time at which the first first run run is started. g. Read the levels of the water in the manometer tubes (h 1, h2, etc.) and measure the water temperature (T C) 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. intervals . 10. Dismantle cell cell 11. Calculate results results 12. Report

Figure 2: General arrangement for constant head permeability test (downward flow) (Courtesy of ELE International, 2007)

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: CONSTANT HEAD PERMEABILITY TEST

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6.0 RESULTS AND CALCULATIONS CALCULATIONS Constant Head Permeability test Location: Pantai Punggur 

Sample no: 2

Operator: Soil description: Light brown sand 

Date:

Method of preparation: lightly compacted in 3 layers  Sample diameter: Sample area, A: Sample dry mass:

80 mm

Sample length:

232 mm

5026 mm2

Sample volume:

1166 mm3

Sample dry density:

16.19 kN/m3

1925 g

S.G. measured/assumed: 2.65  Heights above datum: inlet Manometer a: mm Head difference a to c, H: Flow upwards/downwards Temperature:

Voids ratio: 0.8 mm Manometer b: mm

Heights above datum: outlet mm Manometer c: Distance difference, L: Hydraulic gradients ( H/L)

mm mm mm mm

Reading: Time from start

Time interval, t

Measured flow, Q

Rate of flow, q = Q/t

min.

min.

ml

ml/min

2

2

4

2

6

2

8

2

10

2

15

5

20

5

25

5

30

5

35

5

45

10

1 t 

t

= time

from start 

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: CONSTANT HEAD PERMEABILITY TEST

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a) Plot the graph of q versus 1/t and determine the value of q at 1/ t is equal to zero. b) Use the q from the graph to calculate the permeability.

Calculations: Permeability, k =

q Ai  60

 = _________________ (m/s)

7.0 QUESTIONS

1.

Determine the coefficient coefficie nt of permeability for the given soil sample.

2. Discuss and and give the conclusion conclusion of this test.

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