1 Aims and Objectives

1.1 Aims

This laboratory experiment aims to help students understand how to measure the undrained shear

strength parameter of a saturated clay.

1.2 Objectives

Prepare and measure the shear strength parameters of a saturated clay.

At the end of this lab experiment, students should be able to:

•

Carry out triaxial compression test to measure the shear strength parameters of a soil, and

Analyse the results and its implication in geotechnical design.

2 Theory

LVDT

Air-release

valve

Piston

load cell-

Perspex

cylinder

Rubber

membrane.

Soil sample-

Sintered

bronze disc

Drainage

Pore - water

Loading piston

-'0'- ring

Figure 1 - A Typical Triaxial Cell

Perspex loading

cap-machined to allow

drainage along

bottom face

Brass cap, greased on

bottom face, with central

sintered bronze disc

Thin rubber disc

Flexible drainage pipe

Thin rubber disc

-'0' - rings

Cell

pressure/n+

L Initial specimen length

A = Cross sectional area of specimen

CELL PRESSURE + DEVIATOR STRESS = PRINCIPAL STRESSES

03 = Cell Pressure (all-round or ambient stress)

0₁ = Axial (vertical) stress

x Axial deformation

&₁ = Axial (vertical) strain (x/L)

01-03 = Deviator stress

01-03

W. (1- &₁)

A

Load (W)

CurrentCrossSectional Area(A₁)

03

Undrained failure occurs when the deviator stress reaches a magnitude of 2s, where s, is the

undrained shear strength.

3 Experimental Procedure

You are provided with 4 cylindrical clay specimens, each with an initial length L = 76 mm and initial

diameter D = 38 mm (Initial cross sectional area is A = 0.00113 m2).

You are required to carry out a series of triaxial compression tests at cell pressures (03) of 100, 200,

300 and 400 kN/m² on each of the four specimens provided, which have been prepared from the same

clay sample.

During each test, you should record axial load readings (W) at axial deformations (x) of 0.5, 1.0, 1.5, 2,

4, 6, 8, 10mm etc. up to and including 24 mm as detailed on the accompanying data sheet.

From wet and dry weighings after each test, calculate each specimen's moisture content (%) and unit

weight (kN/m³)./nSPECIMEN NUMBER

Date of test

Length of specimen (mms)

Diameter of specimen (mms)

C.S.A. of specimen (sq.m.)

Wet weight of specimen

Dry weight of specimen (gms)

Moisture Content (%)

Load Cell Constant (kN/div)

Test Cell Pressure (kN/sq.m.)

SPECIMEN NUMBER

Specimen

Deformation

(mms)

X

0

0.5

1

1.5

2

4

6

8

UNDRAINED TRIAXIAL COMPRESSION TEST DATA SHEET

2

3

10

12

14

16

18

20

22

24

Specimen

Deformatio

n (mms)

X

0

0.5

1

1.5

2

SPECIMEN NUMBER

6

8

10

12

14

16

18

20

22

24

&

&=x/L

Strain Load Deviator

Stress

(kN) (kN/sq.m)

W

=W(1-₁)/A

Strain

&

&=x/L

7

3

0.00113

Load

(kN)

W

1

100

3

Deviator

Stress

(kN/sq.m.

=W(1-1)/A

76

38

0.00113

1

200

Specimen

Deformation

(mm)

X

0

0.5

SPECIMEN NUMBER

1

1.5

2

4

6

8

10

12

14

16

18

20

22

24

Specimen

Deformation

(mms)

X

0

0.5

1

1.5

2

SL-1 Lab Script // CIVE224

4

6

8

10

12

14

16

18

20

76

38

0.00113

SPECIMEN NUMBER

22

24

1

300

Strain Load

E

&=x/L

Strain

ધ્રા

&=x/L

2

Deviator

Stress

(kN) (kN/sq.m)

=W(1-₁)/A

W

Load

4

(kN)

W

76

38

0.00113

400

Deviator

Stress

(kN/sq.m.

=W(1-₁)/A

6