1

Conventional Laboratory Testing Methods & Issues

Ajanta Sachan Assistant Professor Civil Engineering IIT Gandhinagar

Geotechnical Engg Structures… Buried right Under your Feet…!!

Hiding World of Geotechnical Engg…!!

Foundations

Tunneling

Shoring

Soil Exploration

2

Purpose of Geotechnical Testing?

ground

Can the soils Support the structure?

What is the impact of Excavation or Filling?

Are the earth and rock Slopes stable?

What type of Foundation is best suited for the structure?

How will the site respond to an Earthquake?

Is the site Contaminated?

Determine potential problems and Avoid surprises!!

Typical Geotechnical Project

construction site

Geo-Laboratory ~ for testing

Design Office ~ for design & analysis

soil properties

3

Issue 1: Bearing Capacity Shear Strength of Soils

Issue 2: Settlement Compressibility parameters of Soils

The issues before designing the CE structure

Solution: 1. Ground Improvement 2. Choice of Foundation 3. Special cases/Problem soils: Specific analysis

If not satisfied…

4

Soils generally fail in shear

strip footing

embankment

At failure, shear stress along the failure surface reaches the shear strength.

failure surface mobilised shear resistance

Issues 1: Bearing Capacity

… Blunders become monuments !

Classic Example: Settlement problem

Issues 2: Settlement

Other Information:

Resting on Shallow Foundation

Supported by soft soil underneath

5

Leaning Tower of Pisa

Soil profile beneath the Tower

6

Relationship between time, inclination and settlement

Non-uniform and overlapping pressure bulbs

Tower silos; Ontario, Canada

Leaning twin silos caused by non uniform settlement in zone of overlapping pressure bulbs

Settlement: Other example

7

You pay for soil investigation whether you carry out or not. Infact you eventually pay more without a soil investigation.

Each and every project is unique for its geotechnical investigations…!!

Importance of Geotechnical Investigations…

Unique?

No Ready-made solution is available!!

8

S : Solid Soil particle

W: Liquid Water (electrolytes)

A: Air Air

v

s

Ve

VVoid ratio,

Three Phases in Soils

Soil Sampling: Before Lab testing

Disturbed Samples: Natural soil structure is modified or destroyed during sampling Representative Samples:

Natural water content and mineral constituents of particular soil layer are preserved

Good for soil identification and water content

Non-representative Samples: Water content altered and soil layers mixed up

Of no use.

Undisturbed Samples: Soil structure and the other mineral properties are preserved to an extent. Some disturbance is always there, e.g. due to stress release.

However it should be minimized in order to have suitable sample for our analysis.

9

Laboratory Test: Index Properties

Index Properties of soil:

Basic soil properties such as (a) Specific gravity (Gs) (b) Grain size distribution (dry/wet Sieve test, Hydrometer test), (c) Liquid Limit (LL), Plastic limit (PL) (d) OMC, Maximum Dry density(Compaction/Proctor test) (e) Permeability (Constant head/Falling head) (f) Relative Density (Minimum & Maximum density for cohesionless soils)

More tests for Problem soils: (a) Shrinkage Limit, Free swell, Swell pressure for Expansive soils (b) Pinhole test, Crumb test for Dispersive soils (c) Chemical Test (PH, Sulphite, Chloride, Iron etc) for soils (may affected with industrial waste or some other waste) (d) Furnace test for Organic Soils (peats etc)

“Representative Disturbed “soil samples are used to perform these tests.

Laboratory Test: Engineering Properties

Engineering Properties of soil:

Consolidation Properties (Oedometer setup) (i) Must to perform for Clayey soils; (ii) Soil parameters obtained: Cc,Cv,Cr, OCR, k

Shear Strength Properties (i) Direct Shear test (for cohesionless soil) (ii) Unconfined Compression test (for cohesive soil)

(iii) Triaxial test (for all soil types; cohesive, cohesionless)

Dynamic Properties (i) Cyclic Triaxial test (ii) Cyclic Simple Shear test (iii) Resonant Column test (iv) Bender Element test

“Undisturbed” soil samples are used to perform these tests.

10

Grain Size Distribution

In Coarse grained soils …... By Sieve analysis (Dry/Wet)

Sieve Analysis Hydrometer Analysis

soil/water suspension

hydrometer

stack of sieves

sieve shaker

In Fine grained soils …... By Hydrometer analysis

: Above 75 m particle size : Below 75 m particle size

Soil Groups Based on its Particle Size

Fine grain soils

Coarse grain soils

0.002 300 80 4.75 0.075

Grain size (mm) (IS code)

Boulder Clay Silt Sand Gravel Cobble

Granular soils or Cohesion less soils

Cohesive soils

Non-Clay minerals

Clay minerals

0.425 2.0

Fine Medium Coarse Fine Coarse

20

Hydrometer (< 75 m size)

Sieve analysis (> 75 m size)

11

Soil Texture

Particle size, shape and size distribution Coarse-textured (Gravel, Sand) Fine-textured (Silt, Clay) Visibility by the naked eye (0.05mm is the approx

limit)

Particle size distribution Sieve/Mechanical analysis or Gradation Test Hydrometer analysis for smaller than .05 to .075 mm

(#200 US Standard sieve)

Particle size distribution curves Well graded Poorly graded 60

10u

DC

D

230

60 10c

DC

D D

Grain Size Distribution

Poorly Graded

Well Graded

Gap Graded

60

30u

DC

D

230

60 10c

DC

D D

Coefficient of Uniformity

Coefficient of Curvature

For Gravel:

Cu < 4 Poorly graded Cu > 4 Well graded or Gap graded

1 < Cc <3 Well graded

For Sand:

Cu < 6 Poorly graded Cu > 6 Well graded or Gap graded

12

Grain Size Distribution Curve

Gravel: Sand:

General Characteristics of Soils Soil Characteristics Gravel, Sand Silt Clay Grain size Granular, Coarse-grained,

particles can be seen through naked eyes

Fine-grained, can not see individual particles

Fine-grained, can not see individual particles

Plasticity and Cohesion Non-plastic, Cohesion less Slightly or no plasticity, Cohesion

Plastic, Cohesive

Effect of grain size distribution (Sieve analysis)

Important Less important Unimportant

Effect of water (Atterberg limits)

Unimportant (except for loose saturated soils under dynamic loadings)

Important Very important

Permeability and Drainage Pervious, Freely draining Less pervious Almost impervious

Compressibility Low Medium High

Shear Strength Depends on relative density (generally high)

Intermediate Depends on consistency (generally poor)

13

Effect of Particle size

Relative Density

Void ratio (e)

1.0

0.8

0.6

0.4

0.2

0

emax

Dr = 0%

e

0%<Dr <100%

emin

Dr = 100%

max

max minr

e eD

e e

IS 2720 (Part XIV) 1983: emin (max density): Vibrating in mould under some surcharge load emax (min density): Pouring in a mould through funnel from ht of 2.5 cm.

(Lambe and Whitman, 1979)

14

Atterberg Limits

Border line water contents, separating the different states of a fine grained soil

Liquid limit

Shrinkage limit

Plastic limit

0 water content

liquid semi-solid brittle-

solid

plastic

Atterberg Limits

(Holtz and Kovacs, 1981)

In percentage

The presence of water in fine-grained soils can significantly affect associated engineering behavior, so we need a reference index to clarify the effects.

15

Group symbols: G - gravel S - sand M - silt C - clay O - organic silts and clay Pt - peat and highly organic soils H - high plasticity L - low plasticity W - well graded P - poorly graded

Soil Classification Systems

Plasticity Chart

Casagrande’s PI-LL Chart

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Liquid Limit

Pla

stic

ity

Ind

ex

A-line

U-line

illite

kaolinite

chlorite

halloysite

16

Typical Values of Atterberg Limits

(Mitchell, 1993)

Consolidation: Oedometer test

17

Consolidation

When a saturated clay is loaded externally,

saturated clay

GL

the water is squeezed out of the clay over a long time (due to low permeability of the clay).

Consolidation Test

~ simulation of 1-D field consolidation in lab.

Field

GL

Lab

undisturbed soil specimen

Dia = 50-75 mm

Height = 20-30 mm

metal ring

(oedometer)

porous stone

18

Consolidation Test: Oedometer Test

Input: Vertical Load, Vertical Displacement

Output: Consolidation parameters (Cv, Cc & Cs); void ratio versus overburden pressure curve; (e-logp); permeability (k)

H -e Relation

saturated clay

GL

q kPa

saturated clay

GL

q kPa

Ho

Time = 0+

e = eo

H

Time =

e = eo - e

average vertical strain =

oH

H

19

H -e Relation

Consider an element where Vs = 1 initially.

e

1

eo

Time = 0+ Time =

average vertical strain =

oe

e

1

H -e Relation

Equating the two expressions for average vertical strain,

oe

e

1

oH

H

consolidation settlement

initial thickness of clay layer

initial void ratio

change in void ratio

20

Overconsolidation ratio (OCR)

original state

log v’

void

ratio

virgin consolidation line

p’ vo’

eo

Field

vo’

'

'

vo

pOCR

Example 1: Oedometer test

e-logp curve (Void ratio versus pressure curve): Incremental Loading & Unloading

0.40

0.45

0.50

0.55

0.60

0.1 1 10

Vo

id R

atio

, e

Log Effective Stress in kg/cm2

Loading: 0.1, 0.2, 0.5, 1.0, 2.0, 4.0, 8.0 Kg/cm2

Unloading: 8.0, 4.0, 2.0, 1.0, 0.5, 0.2, 0.1 Kg/cm2

Compression index (Cc) = 0.1

Re-compression index (Cr) = 0.01

21

Compressibility parameters (Cc & Cr):

log log1 1

s c c c c o avc

o o o c

C H C HS

e e

log1

c c o avc

o o

C HS

e

Settlement for NC soil

Settlement for OC soil

Compressibility parameters Cc & Cr are used in settlement calculations. Cc is the slope of loading curve and Cr or Cs is the slope of unloading curve.

Oedometer test: Coff of consolidation (Cv)

Casagrande Method Taylor Method

Time-settlement analysis at given load in Oedometer test (consolidation test)

1. Casagrande Method (logt method) 2. Taylor Method (√t method)

22

Coefficient of Consolidation (Cv)

t i cS S US 2v

t

c tT

H

Settlement curve (oedometer test at each load):

Casagrade method : t50 (U = 50%)

Tayor method : t90 (U = 90%)

U = Degree of consolidation

T = Time factor

Find coefficient of consolidation (Cv) ?

2v

t

c tT

H

Permeability: k = Cv mv gw

Oedometer test: Time-settlement curve

9.6

9.62

9.64

9.66

9.68

9.7

9.72

9.74

9.76

9.78

9.8

9.82

0 10 20 30 40

Dia

l G

auge

Re

adin

g (m

m)

Square Root of Time

100 kPa vertical stress

Taylor Method

2v

t

c tT

H

Tayor method: t90 (U = 90%)

23

Void ratio versus pressure curve

Void ratio versus Stress (e-p) relationship

mv = av/(1+e0)

Compaction: Proctor test

24

Compaction

A simple ground improvement technique, where the soil is densified through external compactive effort.

+ water =

Compactive effort

Laboratory Compaction Test

- to obtain the compaction curve and define the optimum water content and maximum dry density for a specific compactive effort.

hammer Standard Proctor: Modified Proctor:

• 3 layers

• 25 blows per layer

• 5 layers

• 25 blows per layer

• 2.7 kg hammer

• 300 mm drop

• 4.9 kg hammer

• 450 mm drop

compaction mould

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Example 2: Standard Proctor test

1.791.801.811.821.831.841.851.861.871.881.891.901.911.921.931.941.951.961.97

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Dry

de

nsi

ty (

gm/c

c)

water content (%)

OMC 11.0 %

MDD 1.96 gm/cc

OMC = Optimum Moisture Content

MDD = Maximum Dry Density

Compaction Curve

Water content

Dry

den

sity

(

d)

optimum water content

d, max

- Soil grains densely packed

- Good strength and stiffness

- Low permeability

26

Compaction Curve

What happens to the relative quantities of the three phases with addition of water?

Water content

Dry

den

sity

(

d)

soil

water

air

difficult to expel all air

lowest void ratio and highest

dry density at optimum w

Effect of Compactive Effort

Increasing compactive effort results in:

Lower optimum water content

Higher maximum dry density

E1

E2 (>E1)

Water content

Dry

den

sity

(

d)

27

53

Compaction Control Test

compacted ground

d,field = ? wfield = ?

Compaction

specifications

Compare!

w

d

Shear Strength Testing (Laboratory)

28

Shear Strength Testing (Lab methods)

Shear Strength Lab testing methods: 1. Direct Shear test:

Cohesionless soil (sands, silts) 2. Unconfined Compression test: Cohesive soil (sample can stand by itself) 3. Triaxial test: Mostly compression test a. Unconsolidated Undrained (UU) b. Consolidated Undrained (CU) c. Consolidated Drained (CD)

Unconfined Compression Test (UC test) (Recommended for Cohesive soils)

Input: Vertical Load, Vertical Displacement

Output: Shear Strength under Undrained Conditions (Su)

Platen

Platen

29

Unconfined Compression (UC) Test on Soils

-

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18

Axi

al S

tres

s (k

Pa)

Axial Strain (%)

Test1

Test2

Test3

qu = Unconfined compressive strength c= cohesion Deformation rate =1.25mm/min Sample size = 38 mm dia & 76 mm ht

qu 267 kPa

c 133 kPa

Example 3: Unconfined Compression (UC) test

- Recommended for Cohesive soils

30

Direct Shear Test (Recommended for Cohesionless soils)

Input: Vertical Load, Vertical Displacement, Lateral Load Lateral Displacement

Output: shear strength, friction angle (f)

Direct Shear Test, contd…

Measured Quantities: 1. Vertical Load 2. Vertical Displacement 3. Lateral/Shearing Load 4. Lateral/Shearing Displacement

Interpretations : 1. Shear Strength under Wet

Conditions

31

0

20

40

60

80

100

120

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

She

ar s

tre

ss (k

Pa)

Shear deformation (mm)

Test1 Test2 Test3

Test 1: at 0.5 Kg/cm2 Test 2: at 1.0 Kg/cm2 Test 3: at 1.5 Kg/cm2

Example 4: Direct Shear test

- Recommended for Cohesionless soils

Example 4: Direct Shear test

0.0

0.4

0.8

1.2

0.0 0.5 1.0 1.5 2.0

She

ar s

tre

ss (

kg/c

m2)

Normal stress (kg/cm2)

Test Normal stress

Shear stress at

failure

Shear stress

at failure

(kg/cm2) (kPa) (kg/cm2)

Direct shear test 1 0.5 39.6 0.396

Direct shear test 2 1.0 64.8 0.648

Direct shear test 3 1.5 100.7 1.007

Deformation rate =0.25mm/min Sample size = 60mmx60mmx25mm

f 34 deg

c 0 kPa

32

Shear Stress-shear displacement curves of soils (Direct Shear test)

Triaxial Test

porous stone

impervious membrane

piston (to apply deviatoric stress)

O-ring

pedestal

perspex cell

cell pressure back pressure

pore pressure or

volume change

water

soil sample at failure

failure plane

Loading conditions: Static/Monotoinc loading (compression is common)

Measures shear strength parameters of soil: cohesion & friction angle

33

Triaxial Testing Setup

Soil specimen

Triaxial setup

Control Panel

Input: Vertical Load, Vertical Displacement, Pore pressure, Cell pressure

Output: Shear Strength properties of soil under UU, CU, CD Conditions: friction angle (f), cohesion (c)

Triaxial Test, contd…

Interpretations : 1. Shear Stress-Strain Relationship under triaxial

compression/extension Conditions 2. Volumetric Response or Void ratio change 3. Shear Strength under Undrained/Drained triaxial shearing Conditions

Measured Quantities: 1. Vertical Load 2. Vertical Displacement 3. Confining Pressure 4. Back Pressure/Excess

Pore Pressure 5. Volume change by

measuring expelled water volume

34

Types of Triaxial Tests

Under all-around cell pressure c

Shearing (loading)

Is the drainage valve open? Is the drainage valve open?

deviatoric stress ()

yes no yes no

Consolidated sample

Unconsolidated sample

Drained loading

Undrained loading

Shear failure

At failure, shear stress along the failure surface () reaches the shear strength (f).

35

Mohr-Coulomb Failure Criterion

f tan cf

c

f

cohesion friction angle

f is the maximum shear stress the soil can take without failure, under normal stress of .

f

Mohr-Coulomb Failure Criterion

f tanff c

Shear strength consists of two components: cohesive and frictional.

f

f

f

c

f tan f

c

frictional component

36

Mohr Circles & Failure Envelope

Y

Initially, Mohr circle is a point

c

c

c

c+

The soil element does not fail if the Mohr circle is contained within the envelope

GL

Mohr Circles & Failure Envelope

Y

c

c

c

GL

As loading progresses, Mohr circle becomes larger…

.. and finally failure occurs when Mohr circle touches the envelope

37

Orientation of Failure Plane

Y

c

c

c

GL

c+

90+f

f

45 + f/2

Failure plane oriented at 45 + f/2 to horizontal

45 + f/2

Y

Envelopes in terms of & ’

Identical specimens initially subjected to different isotropic stresses (c) and then loaded axially to failure

c

c

c

c

f

Initially… Failure

uf

At failure,

3 = c; 1 = c+f

3’ = 3 – uf ; 1’ = 1 - uf

c, f

c’, f’

in terms of

in terms of ’

38

1-

3 Relation at Failure

X

soil element at failure

3 1

X 3

1

)2/45tan(2)2/45(tan231 ff c

)2/45tan(2)2/45(tan213 ff c

UU: Unconsolidated Undrained Test

-

39

Test 1: at 100 kPa Test 2: at 200 kPa Test 3: at 300 kPa

Example 5: UU Triaxial test

Deformation rate =0.4 mm/min Sample size = 38 mm dia & 76 mm ht

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25

Axi

al s

tra

a (k

Pa

)

Axial strain (%)

Test1

Test2

Test3

Example 5: UU Triaxial test

ccosf = asinf = tanx

- a is intercept of q-p curve - x is slope angle of q-p curve

3 d q p

(kPa) (kPa) (kPa) (kPa)

Test 1 100 531.1 265.55 365.55

Test 2 200 957.8 478.9 678.9

Test 3 300 1163.3 581.65 881.65

q = (1-3)/2

p = (1+3)/2

0

100

200

300

400

500

600

0 200 400 600 800 1000

q (k

Pa)

p (kPa)

f 38 deg

c 57 kPa

40

Thank You

Time Rate of Settlement

For open clay layer with two way drainage use curve for V=1

Assumption of pore pressure distribution under the given stress conditions

IS 8009 (Fig 13)

41

Isotropic Compression Test Increase in Cell Pressure

o

Z

Y

X

o

o

o

o

o

Measured Quantities: 1. Cell Pressure 2. Volume Change & Pore Pressure 3. Axial Displacement

Interpretations : 1. Consolidation parameters, Transient Flow, T50, T100

2. Stress-strain relationship, Cc and Cs

3. Sense of Anisotropy by ea-ev relationship

CU: Consolidated undrained Test

-

42

Output: - Axial stress- axial strain curve

- Pore pressure-axial strain curve

A typical CU test

Example 6: CU Triaxial test

f'= 27 deg

c' = 0 kPa

Example 6: CU Triaxial test

-100

-50

0

50

100

150

200

250

-15 -10 -5 0 5 10 15 20ea (%)

Exc

ess

po

re p

ress

ure

(kP

a)

Extension, OCR=1

Extension, OCR=10

Compression, OCR=1

Compression, OCR=10

0

20

40

60

80

100

120

140

160

180

-15 -10 -5 0 5 10 15 20ea (%)

Dev

iato

ric

stre

ss (

kPa)

Extension, OCR=1

Extension, OCR=10

Compression, OCR=1

Compression, OCR=10

43

CD: Consolidated Drained Test

Output: - Axial stress- axial strain curve

- Volumetric strain -axial strain curve

A typical CD test

Example 7: CD Triaxial test

0

100

200

300

400

500

0 5 10 15 20 25 30

d (K

Pa)

ea (%)

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30

Vo

lum

etri

c st

rain

(%)

ea (%)

f = 26.6 deg

c = 0 kPa

Confining pressure = 276 kPa

Total three triaxial tests at three different confining pressures need to be performed to obtain shear strength parameters of soil under consolidated drained (CD) conditions.

44

Example 7: CD Triaxial test

-4

-2

0

2

4

6

8

10

-14 -10 -6 -2 2 6 10 14 18 22 26ea (%)

Vo

lum

etri

c st

rain

(%

)

Extension, OCR=1

Extension, OCR=10

Compression, OCR=1

Compression, OCR=10

0

50

100

150

200

250

300

350

400

450

500

-14 -10 -6 -2 2 6 10 14 18 22 26

ea (%)

Dev

iato

ric

stre

ss (

kPa)

Extension, OCR=1

Extension, OCR=10

Compression, OCR=1

Compression, OCR=10

Other Soil Properties: Dynamic Properties

45

Soil Properties

Monotonic Loading (Shear strength properties of soil)

Angle of Internal Friction (f)

Cohesion (c)

Dynamic Loading (Dynamic properties of soil)

Shear Modulus (G)

Damping Ratio (D)

Dynamic properties of Soil

Shear Modulus, G = .VS2

Shear wave velocity = VS (m/sec)

Mass density = (g/g) (Kg/m3)

Unit weight of soil = g (KN/m3)

Acceleration of gravity = g (m/sec2)

Damping, D = decay in energy

Shear Modulus (G) is measured in KN/m2 & Damping (D) in %

46

Dynamic properties of soil

Low Strain Amplitude test

For strains (10-6% to 10-4%)

Frequency range: 10 Hz to 200Hz

Vibratory loading (Rotating Machinery etc)

High Strain Amplitude test

For strains (10-4% to 10-2%)

Frequency range: 0.1 Hz to 2 Hz (in general)

Blast loading, Earthquake

Dynamic properties (Lab test)

High Strain Amplitude test

Cyclic Triaxial Test

Cyclic Direct Simple Shear Test

Low Strain Amplitude test

Resonant Column Test

Bender Element Test

47

Cyclic Triaxial Test (High strain amplitude test)

Dynamic properties of soil using Cyclic Triaxial system: 1. Shear Modulus (G) 2. Damping ratio (D)

Cyclic Triaxial Test

DDamping EModulus Young Dynamic

dStress Dynamic aeStrain Axial

48

Cyclic Simple Shear Test (High strain amplitude test)

Digitally controlled Electro-mechanical actuators are used to apply the stress or strain controlled loading

Output: Shear modulus (G), Damping (D)

Cyclic Simple Shear Test

DDamping GusShearModul

gnShearStraisShearStres

49

Resonant Column Test (Low strain amplitude test)

The basic principle of the resonant column device is to excite one end of a confined cylindrical soil specimen in a fundamental mode of vibration by means of torsional or longitudinal excitation. Once the fundamental mode of resonance frequency is established, measurements are made of the resonance frequency and amplitude of vibration from which wave propagation velocities and strain amplitudes are calculated using the theory of elasticity.

The Resonant Column Test provides laboratory values of Shear modulus (G) and Damping ratio (D).

Resonant Column Test (Low strain amplitude test)

(a) Specimen is excited at the bottom and the response is picked up at the top (velocity or acceleration) (b) Driving force is applied on the top. The response pickup is also placed on the top

With known value of the resonant frequency it is possible to back-calculate the velocity (vs or vl) of the wave propagation and thereby G or E After measuring the resonant condition, the drive system is cut of and the specimen is brought to a state of free vibration. Damping is determined by observing the decay pattern

50

tiCt e)(

Acc.

ff

Resonant freq. f1+

Sample Geometry+

End restraint+

Wave equation (torsion)

( 2

1220 2

Ts F

fHvG

Resonant Column Test: Determination of Shear Modulus of soil (G)

Resonant Column Test: Damping properties of soil (D

D = 1/2·1

51

Bender Element Test (Low strain amplitude test)

Bender Elements (made by Piezoelectric material)

Bender Element Test (Low strain amplitude test)

Piezo-ceramic elements distort or bend when subjected to a change in voltage. Two Piezoelectric bender elements are placed opposite one another and inserted a small distance into a soil sample. One bender element work as source and other as receiver. The voltage in one element is varied creating shear waves through the sample, which are received by the opposite element. The input voltage, (created using a function generator) and the received signal are recorded continuously using an oscilloscope, allowing the travel time of the shear waves to be measured from which the dynamic elastic shear modulus (G) can be determined. Bender elements provide a reliable, cost effective alternative to undertaking locally instrumented stress path triaxial tests and can be readily performed on unconfined samples in the laboratory.