UNIVERSITI TUN HUSSEIN ONN MALAYSIA

CENTRE OF DIPLOMA STUDIES

2014/2015

2DAB

GEOTECHNICAL TECHNOLOGY

DAB 20402

SECTION 1

LAB REPORT

LECTURER’S NAME: TN HJ AMIR KHAN BIN SUWANDI

NAME:

NAME MATRIC NO.

MOHAMAD FAEIZ BIN MOHAMAD SHUKRI AA130741

MUHAMMAD NUR FAHMY IZZUDDIN BIN SHARIM AA131258

NURUL ZETTY IQMA BINTI ABU SAMAH AA130984

NUR HANANI NADZIRAH BINTI MOHD JAFFRI AA131287

1.0 OBJECTIVE

1.1 Objective

To determine permeability of soils of intermediate and low permeability (less than

10-4 m/s), i.e. silts and clays.

1.2 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.

2.0 THEORY

In the falling head test a relatively short example 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).h1h2

Permeability, k = aL

A (t 2−t 1)loge (h1

h2¿……….. 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 millimeters. Eqn

(1) then becomes Eqn (2).

Permeability, k = aL

Ax 60 t loge (h1

h2¿(m/s)………..Eqn (2)

To convert natural logarithms to ordinary (base 10) logarithms, multiply by 2.303. if k is

expressed in m/s, the above equation becomes Eqn (3).

Permeability, k = 2.303 aL

1000 xAx 60t log10 (h1

h2¿(m/s)………..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

3.0 PRECEDURES + APPARATUS

3.1 Test Equipment

1. Permeameter cell, comprising:

Cell body, with cuttingedge (core cutter), 100mm diameter and 130mm long.

Perforated base plate with straining rods and wing nuts.

Top clamping plate.

Connecting tube and fittings.

Figure 1: Compaction permeameter

3.2 Procedures

1. Assemble apparatus,

a. The apparatus is set up as shown in Figure 2. The volume of water passing

through a sample of low permeability is quite small and 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. The areas of cross-section of the three manometer tubes should be determined

as follows for 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. Weigh the beaker containing water from the tube (weighings should be

to the nearest 0.01g)

v. The diameter of the manometer can be calculated as follows:

Diameter, a = 1000 mw

h2−h1mm2

If mw = mass 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. Prepare cell,

a. Dismantle the cell,

b. Check the cell body is clean and dry, and weigh 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

4.0 RESULTS – DATA OBTAINED

Falling Head Permeability Test

Location: Geothecnical Laboratory Sample no: A

Operator: Date: 10/11/2014

Soil description:

Method of preparation:

Sample diameter, D: 99.88 mm Sample length, L: 140.13 mm

Sample area, A: 7835.14 mm2 Sample volume, V: 1097.94 cm3

Mass of mould: 1852 g Mass of sample + mould: 4096 g

Mass of sample: 2244 g

S.G. measured/ assumed: Voids ratio:

Bulk density: kN/m3 Sample volume, V: cm3

Moisture content: % Test temperature: 25 ◦c

Standpipe diameter: 3.92 mm Standpipe area, a: 12.07 mm2

Reading:

Reference point

Height above datum, y

(mm)

Height above outlet, h (mm)

Test Height ratios

No. Time, t (min)

1 900 800 1 18.47 9:8

2 800 700 2 20.93 8:7

3 700 600 3 22.72 7:6

4 600 500 4 24.40 6:5

Calculations:

Permeability, k = 2.303 aL1000 xAx 60t log10 (

h1

h2¿(m/s)

5.0 CALCULATIONS

6.0 CONCLUSIONS

The coefficient of permeability of a soil describes how easily a liquid will move through a

soil. It is also commonly referred to as the hydraulic conductivity of a soil. This factor can

be affected by the viscosity, or thickness (fluidity) of a liquid and its density. The number

can also be affected by the void size, or region of non-soil, void continuity, and soil particle

shape and surface roughness. It is an important factor when determining the rate at which a

fluid will actually flow through a particular type of soil.

A flow net is a graphical method by which one can characterize the flow of a liquid through a

soil. When performing the calculations associated with a flow net, it is important to know

the coefficient of permeability, or hydraulic gradient, of a soil.

7.0 QUESTIONS - DISCUSSION

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

Based on calculation done before for each references point, we should do an average to

for all point to get value of permeability.

References point 1= 5.85×10-7

References point 2= 5.85×10-7

References point 3= 6.49×10-7

References point 4=6.85×10-7

(5.85×10 -7 ) + (5.85×10 -7 ) + (6.49×10 -7 ) + (6.85×10 -7 ) = 6.26×10-7

4

2. Give a conclusion for this test.

The test is totally different from the constant head methods in its initial setup. But

actually the advantage to the falling-head method is that it can be used for both

fine-grained and coarse-grained soils. The soil sample is first saturated under a

specific head condition. The water is then allowed to flow through the soil

without maintaining a constant pressure head.

8.0 APPENDICES