Falling Head Permeability - 011

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 1. 2. GROUP MEMBER NAMES

3. 4. 5.

LECTURER/ INSTRUCTOR/ TUTOR NAME REPORT RECEIVED DATE MARKS

EXAMINER COMMENT

ATTENDANCE/ DISCIPLINE & INVOLVEMENT

/15%

DATA ANALYSIS

/20%

RESULT

/20%

DISCUSSION

/25%

CONCLUSION

/20%

TOTAL

/100% RECEIVED STAMP

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

: …………………………………………

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: GEOTECHNICAL AND TRANSPORTATION ENGINEERING TEST TITLE : FALLING HEAD PERMEABILITY TEST

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1.0 OBJECTIVE TO DETERMINE PERMEABILITY OF SOILS OF INTERMEDIATE AND LOW PERMEABILITY -4 (LESS THAN 10 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).

Permeability, k 

h  aL log e  1  ………..Eqn (1) A(t 2  t1 )  h2 

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).

Permeability, k 

h  aL log e  1 (mm / s ) ………..Eqn (2) Ax60t  h2 

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).

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: GEOTECHNICAL AND TRANSPORTATION ENGINEERING TEST TITLE : FALLING HEAD PERMEABILITY TEST

Permeability, k 

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h  2.303aL log10  1 (m / s ) ………..Eqn (3) 1000xAx60t  h2 

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)

FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: GEOTECHNICAL AND TRANSPORTATION ENGINEERING TEST TITLE : FALLING HEAD PERMEABILITY TEST

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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:

diameter, a 

vi.

1000 m w 2 mm h1  h2

If mw = mass of water (g), h1 = initial level in tube (mm), h2 = final level in tube (mm), 2 A = area of cross-section of tube (mm ) 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 h 3, and when it reaches h2, then stop the clock, d. Close screw clip at inlet.

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DEPARTMENT: GEOTECHNICAL AND TRANSPORTATION ENGINEERING TEST TITLE : FALLING HEAD PERMEABILITY TEST

EDITION: REVIEW NO.: EFFECTIVE DATE: AMENDMENT DATE:

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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

EDITION: REVIEW NO.: EFFECTIVE DATE: AMENDMENT DATE:

TEST TITLE : FALLING HEAD PERMEABILITY TEST

1/12/11 24/3/11

6.0 RESULTS AND CALCULATIONS Falling Head Permeability test Location: Operator:

Sample no: Date:

Soil description: Method of preparation: Sample diameter, D: Sample area, A: Mass of mould: Mass of sample:

99.075 7709.35 1014.5 1703.4

mm 2 mm g g

S.G. measured/assumed: Bulk density, : Moisture content:

16.43 kN/m 10 %

Standpipe diameter:

4.05 mm

Sample length, L: Sample volume, V: Mass of sample + mould:

3

Voids ratio: Dry density, : Test temperature:

232 mm 3 1166 cm 2717.9 g

16.19 kN/m c

Standpipe area, a:

12.8

mm

3

2

Reading: Reference point

Height above datum, y (mm)

Height above outlet, h (mm)

1 2 3 4

900 800 700 600

800 700 600 500

Calculations:

Permeability, k 

h  2.303aL log10  1 (m / s ) 1000xAx60t  h2 

k1 =

= 1.13 x 10-5 m/s

(

)

Test No. 1 2 3 4

Time, t (s) 4 10 15 20

Height ratios 1.125 1.142 1.167 1.200

k2 =

(

)

(

)

(

)

= 5.14 x 10-6 m/s

k3 = = 3.96 x 10-6 m/s

k4 = = 3.51 x 10-6 m/s

k=

(

) (

) (

)

=

= 5.98 x 10-6 m/s

7.0 QUESTIONS

1. Determine the coefficient of permeability for the given sample of soil. 2. Give a conclusion for this test.