Falling Head Permeability - 011

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FACULTY OF CIVIL & ENVIRONMENTAL

ENGINEERING

DEPT.OF GEOTECHNICAL AND

TRANSPORTATION ENGINEERING

GEOTECHNICAL ENGINEERING LABORATORY

REPORT

SUBJECT CODE

TEST CODE & TITLE COURSE CODE TESTING DATE STUDENT NAME GROUP

GROUP MEMBER NAMES

1. 2. 3. 4. 5.

LECTURER/ INSTRUCTOR/ TUTOR NAME

REPORT RECEIVED DATE

MARKS ATTENDANCE/ DISCIPLINE & INVOLVEMENT /15% DATA ANALYSIS /20% RESULT /20% DISCUSSION /25% CONCLUSION /20% TOTAL /100%

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STUDENT CODE OF ETHIC

(SCE)

DEPT. OF GEOTECHNICAL AND TRANSPOTATION 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.

_________________

Student Signature

Name : ………

Matric No. : ………

Date : ………

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FACULTY: CIVIL & ENVIRONMENTAL ENG. PAGE NO.: 1/5 DEPARTMENT: GEOTECHNICAL AND

TRANSPORTATION ENGINEERING

EDITION: REVIEW NO.:

TEST TITLE : FALLING HEAD PERMEABILITY TEST EFFECTIVE DATE: 1/12/11 AMENDMENT DATE: 24/3/11 1.0 OBJECTIVE

TO DETERMINE PERMEABILITY OF SOILS OF INTERMEDIATE AND LOW PERMEABILITY (LESS THAN 10-4 m/s), I.E. SILTS AND CLAYS.

2.0 LEARNING OUTCOME

At the end of this experiment, students are able to:

 Describe the general accepted practice to determine the coefficient of permeability of silts and clays.

 Identify the relationship between permeability and pore size of the fine grained soils.

 Measure the coefficient of permeability of silts and clays. 3.0 THEORY

In the falling head test a relatively short sample is connected to a standpipe which provides both the head of water and the means of measuring the quantity of water flowing through the sample. Several standpipes of different diameters are normally available from which can be selected the diameter most suitable for the type of material being tested.

In permeability tests on clays, much higher hydraulic gradients than are normally used with sands can be applied, and are often necessary to induce any measurable flow. The cohesion of clays provides resistance to failure by piping at gradients of up to several hundred, even under quite low confining or surcharge pressures. Dispersive clays however are very susceptible to erosion at much lower gradient.

The falling head principle can be applied to an undisturbed sample in a sampling tube and to a sample in an oedometer consolidation cell. The equation used in determine the permeability of fine grained soils is given in Eqn (1).

















2 1 1 2

log

)

(

,

h

t

A

aL

k

ty

Permeabili

_e ………..Eqn (1)

The time difference (t2-t1) can be expressed as the elapsed time, t (minutes). The heights h1 and h2 and

the length, L are expressed in millimetres, and the areas A and a in square millimetres. Eqn (1) then becomes Eqn (2).

)

/

(

log

60 ,

2 1

s

mm

h

t

Ax

aL

k

ty

Permeabili

_e

_













………..Eqn (2)

To convert natural logarithms to ordinary (base 10) logarithms, multiply by 2.303. If k is epxressed in m/s, the above equation becomes Eqn (3).

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PERMEABILITY TEST DATE: AMENDMENT DATE: 24/3/11

)

/

(

log

60 1000

303 .

2 ,

2 1 10

m

s

h

t

xAx

aL

k

ty

Permeabili

_













………..Eqn (3)

Where: a = area of cross-section of standpipe tube, A = area of cross section of sample

h1 = heights of water above datum in standpipe at time t1

h2 = heights of water above datum in standpipe at time t2

L = heights of sample t = elapsed time in minutes

4.0 TEST EQUIPMENTS

1. Permeameter cell, comprising:

Cell body, with cutting edge (core cutter), 100 mm diameter and 130 mm long. Perforated base plate with straining rods and wing nuts.

Top clamping plate.

Connecting tube and fittings.

Figure 1: Compaction permeameter (Courtesy of ELE International, 2007)

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FACULTY: CIVIL & ENVIRONMENTAL ENG. PAGE NO.: 3/5 DEPARTMENT: GEOTECHNICAL AND

TRANSPORTATION ENGINEERING

TEST TITLE : FALLING HEAD PERMEABILITY TEST EFFECTIVE DATE: 1/12/11 AMENDMENT DATE: 24/3/11 5.0 PROCEDURES 1. Assemble apparatus,

a. Set up the apparatus as shown in Figure 2. The volume of water passing through a sample of low permeability is quite small and a continuous supply of de-aired water is not necessary, but the reservoir supplying the de-airing tank should be filled with distilled or de-ionised water

2. Calibrate manometer tubes,

a. Determined the areas of cross-section of the three manometer tubesfor each tube: i. Fill the tube with water up to a known mark near the top of the scale,

observed to the nearest mm,

ii. Run off water from the tube into a weighted beaker, until the level in the tube has fallen by about 500mm or more,

iii. Read the new water level on the scale, to the nearest mm,

iv. Weight the beaker containing water from the tube (weighings should be to the nearest 0.01g)

v. Calculated the diameter of manometer as follows:

2 1

1000

,

h

m

a

diameter

w





mm2 If mw = mass of water (g),

h1 = initial level in tube (mm),

h2 = final level in tube (mm),

A = area of cross-section of tube (mm2)

vi. Repeat the measurements two or three times for each tube, and average the results.

3. Preparing cell,

a. Dismantle the cell,

b. Make sure the cell body is clean and dry, and weight it to the nearest 0.1g, c. Measure the mean internal diameter (D) and length (L) to the nearest 0.5mm 4. Prepare sample,

a. Undisturbed sample can be taken by means of core cutter.

b. Make sure that the sample is a tight fit in the body and there are no cavities around the perimeter through which water could pass,

5. Assemble cell 6. Connect cell

7. Saturate and de-air sample 8. Fill manometer system 9. Run test

a. Open screw clip at inlet to allow water to flow down through the sample, and observe the water level in the standpipe,

b. As soon as it reaches the level h1, start the timer clock,

c. Observe and record the time when the level reaches h3, and when it reaches h2, then

stop the clock,

d. Close screw clip at inlet.

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AMENDMENT

DATE: 24/3/11

10. Test is repeated

11. Permebeabilty is calculated 12. Result reported

Figure 2: Falling head permeability cell with manometer tubes (Courtesy of ELE International, 2007)

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DEPARTMENT: GEOTECHNICAL AND TRANSPORTATION ENGINEERING

TEST TITLE : FALLING HEAD PERMEABILITY TEST

EFFECTIVE

DATE: 1/12/11 AMENDMENT

DATE: 24/3/11

6.0 RESULTS AND CALCULATIONS

Falling Head Permeability test

Location: Sample no:

Operator: Date:

Soil description: Method of preparation:

Sample diameter, D: 99.075 mm Sample length, L: 232 mm Sample area, A: 7709.35 mm2 Sample volume, V: 1166 cm3 Mass of mould: 1014.5 g Mass of sample + mould: 2717.9 g Mass of sample: 1703.4 g

S.G. measured/assumed: Voids ratio:

Bulk density, : 16.43 kN/m3 Dry density, : 16.19 kN/m3 Moisture content: 10 % Test temperature: c

Standpipe diameter: 4.05 mm Standpipe area, a: 12.8 mm2 Reading: Reference point Height above datum, y (mm) Height above outlet, h (mm) Test Height ratios No. Time, t (s) 1 900 800 1 4 1.125 2 800 700 2 10 1.142 3 700 600 3 15 1.167 4 600 500 4 20 1.200 Calculations: