7. InSituTesting Website

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I n situ testing andmonitoring

Prof. Ing. Guido Gottardi


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Introduction

Geotechnical investigations:

• Laboratory tests• In situ testing

•Monitoring

European Standard in force:

Eurocode 7 - Geotechnical design

[UNI EN 1997-2:2007]

•Part 1: General rules

Basis of geotechnical design

Observational method

•Part 2: Ground investigation and testing


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Geotechnical investigations:• Laboratory tests

• In situ testing

•Monitoring

COMPARISON

advantages / disadvantages

In situ and laboratory tests are

COMPLEMENTARY

Boundary conditions

Representativeness

Precision

Speed

Costs

……..


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Significant volume

Examples from: UNI EN 1997-2:2007 - Annex B

Recommendations for the spacing and depth of

investigations

z a ≥ 6 m;

z a ≥ 3,0bF z a ≥ 1,5·bB


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Example of geotechnical design

1) Stability

2) SettlementsSoil parameters

Significant volume for embankments

(from UNI EN 1997-2:2007):

0,8h


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Soil sampling from UNI EN 1997-2:2007


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In situ testing

Table from: Fernando Schnaid (2009). In situ

testing in geomechanics. Ed. Taylor & Francis

Commercial in situ testing techniques


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1) Standard penetration test (SPT)

Objectives

•The objectives of the standard penetration test are the

determination of the resistance of soil at the base of a

borehole to the dynamic penetration of a split barrel

sampler (or solid cone) and the obtaining of disturbed

samples for identification purposes.

•The sampler shall be driven into the soil by dropping a

hammer of 63,5 kg mass onto an anvil or drive head

from a height of 760 mm. The number of blows ( N)

necessary to achieve a penetration of the sampler of

300 mm (after its penetration under gravity and below a

seating drive) is the penetration resistance.

•The test should be used mainly for the determination of

the strength and deformation properties of coarse soil.

•Valuable additional data may also be obtained in other

types of soil.


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Schematic view of SPT using donut hammer, rope

and cathead method (Schnaid, 2009)


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SPT split-spoon sampler: (a) IRTP 1988 and (b)ASTM D 1586 (1999) - from Schnaid (2009)


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Examples of use of test results and derived values

Soil properties in granular materials

•Recommended relationship between φ and NSPT (Peck et

al , 1974 and Mitchell and Lunne, 1978)

•Relationship between Dr and NSPT


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2) Cone penetration and piezocone

penetration tests (CPT, CPTU)

Objectives

•The objective of the cone penetration test (CPT) is to

determine the resistance of soil and soft rock to the

penetration of a cone and the local friction on a sleeve.

Terminology:


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•The CPT consists of pushing a cone penetrometer

vertically into the soil using a series of push rods. Thecone penetrometer shall be pushed into the soil at a

constant rate of penetration. The cone penetrometer

comprises the cone and if appropriate a cylindrical shaft

or friction sleeve. The penetration resistance of the cone

(qc) as well as, if appropriate, the local friction on the

friction sleeve shall be measured.

•For mechanical CPTs, the measurements are generally

made remotely.

Begemann type cone with friction sleeve


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•For electrical CPTs, all measurements shall be made

by sensors contained in the cone penetrometer.

•The piezocone penetration test, CPTU, is an electrical

CPT, which includes additional instrumentation to

measure the pore water pressure during penetration at

the level of the base of the cone.


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Truck mounted a CPT unit

Saturation


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•

The CPTU results should be used mainly for thedetermination of a soil profile together with results from

sampling by drilling and excavations or in comparison with

other field tests.

•The results may also be used for the determination of

geotechnical parameters such as the strength and deformation

properties of soil and soft rock provided penetration is possible.

CPT interpretation from Schnaid (2009)


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Pore water effects:

-In soft clay: qt =qc+u2(1-a)

-In sand: qt =qc

With

a=A N /AT :net area ratio from laboratory calibration

qc : measured cone resistance

qt : correct cone resistance


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Soil type classification charts


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Relationship between qcand ϕ ’ peack for uncemented

normally consolidated quartz

sand (Durgunoglu and

Mitchell, 1975)

Dissipation test


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3) Field vane test (FVT)


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4) Flat dilatometer test (DMT)Objectives

•The objectives of the flat dilatometer test are the

determination of the in-situ strength and deformation

properties of soil by expanding a thin circular steel

membrane mounted flush on one face of a blade-shaped

steel probe inserted vertically into the ground.

•The test consists of measuring the pressures when themembrane is flush with the blade and just begins to move

and when the displacement in the centre of the membrane

reaches 1,10 mm into the soil. The test shall be performed at

selected depths or in a semi-continuous manner.


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•

The results of DMT tests may be used to obtaininformation on soil stratigraphy, in-situ state of stress,

deformation properties and shear strength.

•The DMT test should primarily be used in clays, silts and

sands where particles are small compared to the size of the

membrane.

Typical DMT in clay (Marchetti et al., 2007)

'

0v

00 D

00

01 D

σ

u p K

u p p p I

−

=

−

−

= Material index

Horizontal stress index

( )01 D p p7 ,34 E −= Dilatometer modulus


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5) Pressuremeter tests (PMT)

Objectives•The objective of the pressuremeter test is to measure in-situ

the deformation of soil and soft rock caused by the expansion

of a cylindrical flexible membrane under pressure.

•The test consists of inserting a probe containing a cylindrical

flexible membrane into the ground either into a pre-formed

borehole, or by self-boring or by full displacement pushing.

Once at a predetermined depth the membrane is expandedunder pressure and readings of pressure and expansion are

recorded until a maximum expansion for the particular device

is reached.


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•The test should be used to derive strength and/or

deformation parameters of the ground or specific

pressuremeter parameters.

•The results may be used to derive stress-strain curves in

fine soil and soft rock.


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6) Plate loading test (PLT)Objectives

•The objective of the plate loading test is the determination of

the vertical deformation and strength properties of soil and

rock masses in-situ by recording the load and the

corresponding settlement when a rigid plate modelling a

foundation is loading the ground.

•The plate loading test shall be carried out on a thoroughly

levelled and undisturbed surface either at ground level or on

the bottom of an excavation at a certain depth or the bottom of

a large diameter borehole, an exploration shaft or gallery.

Plates

Idraulic jack

Manometer

Micrometer

Micrometersupport

Counterweight


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7) Geophysical tests

Seismic refraction (SR)

Surface waves (SASW)

Crosshole Test (CHT)

Downhole test (DHT)

Common applications:

-Ground characterization

-Small strain stiffness G0

Recorder

Recorder

Receiver

Receiver

Wave generator

Wave generator

Cross hole

Down hole


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Monitoring

• Measurement of ground water pressure

• Measurement of deformation

Inclinometer

Soft

clay Drains

Tempoprary

Overload

Filter

Preload

Shallow extensometer

Deep extensometer

Piezometers


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Measurement of ground water pressure

Open standpipe piezometer

Piezometer

Schematic of open standpipe piezometer

installed in a borehole


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Casagrande piezometer

Diagram of borehole with a

Casagrande piezometer


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Driven-in piezometer

Cambridge driven-in

piezometer (Ater Parry, 1971)


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Measurement of deformation

Inclinometer

Principal of Conventional Inclinometer Operation (After

Dunnicliff, 1988, 1993)


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Extensometer

Schematic of Probe Extensometer with Magnet/Reed

Switch Tansducer, Installed in a Borehole (After

Dunnicliff, 1988, 1993)


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Extensometer

Multiple Position Borehole Extensometer Installed from

Ground Surface

7. InSituTesting Website

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