7. InSituTesting Website
Transcript of 7. InSituTesting Website
-
8/20/2019 7. InSituTesting Website
1/38
I n situ testing andmonitoring
Prof. Ing. Guido Gottardi
-
8/20/2019 7. InSituTesting Website
2/38
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
-
8/20/2019 7. InSituTesting Website
3/38
-
8/20/2019 7. InSituTesting Website
4/38
Geotechnical investigations:• Laboratory tests
• In situ testing
•Monitoring
COMPARISON
advantages / disadvantages
In situ and laboratory tests are
COMPLEMENTARY
Boundary conditions
Representativeness
Precision
Speed
Costs
……..
-
8/20/2019 7. InSituTesting Website
5/38
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
-
8/20/2019 7. InSituTesting Website
6/38
-
8/20/2019 7. InSituTesting Website
7/38
Example of geotechnical design
1) Stability
2) SettlementsSoil parameters
Significant volume for embankments
(from UNI EN 1997-2:2007):
0,8h
-
8/20/2019 7. InSituTesting Website
8/38
Soil sampling from UNI EN 1997-2:2007
-
8/20/2019 7. InSituTesting Website
9/38
In situ testing
Table from: Fernando Schnaid (2009). In situ
testing in geomechanics. Ed. Taylor & Francis
Commercial in situ testing techniques
-
8/20/2019 7. InSituTesting Website
10/38
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.
-
8/20/2019 7. InSituTesting Website
11/38
Schematic view of SPT using donut hammer, rope
and cathead method (Schnaid, 2009)
-
8/20/2019 7. InSituTesting Website
12/38
SPT split-spoon sampler: (a) IRTP 1988 and (b)ASTM D 1586 (1999) - from Schnaid (2009)
-
8/20/2019 7. InSituTesting Website
13/38
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
-
8/20/2019 7. InSituTesting Website
14/38
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:
-
8/20/2019 7. InSituTesting Website
15/38
•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
-
8/20/2019 7. InSituTesting Website
16/38
•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.
-
8/20/2019 7. InSituTesting Website
17/38
-
8/20/2019 7. InSituTesting Website
18/38
Truck mounted a CPT unit
Saturation
-
8/20/2019 7. InSituTesting Website
19/38
•
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)
-
8/20/2019 7. InSituTesting Website
20/38
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
-
8/20/2019 7. InSituTesting Website
21/38
-
8/20/2019 7. InSituTesting Website
22/38
Soil type classification charts
-
8/20/2019 7. InSituTesting Website
23/38
Relationship between qcand ϕ ’ peack for uncemented
normally consolidated quartz
sand (Durgunoglu and
Mitchell, 1975)
Dissipation test
-
8/20/2019 7. InSituTesting Website
24/38
3) Field vane test (FVT)
-
8/20/2019 7. InSituTesting Website
25/38
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.
-
8/20/2019 7. InSituTesting Website
26/38
•
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
-
8/20/2019 7. InSituTesting Website
27/38
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.
-
8/20/2019 7. InSituTesting Website
28/38
•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.
-
8/20/2019 7. InSituTesting Website
29/38
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
-
8/20/2019 7. InSituTesting Website
30/38
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
-
8/20/2019 7. InSituTesting Website
31/38
Monitoring
• Measurement of ground water pressure
• Measurement of deformation
Inclinometer
Soft
clay Drains
Tempoprary
Overload
Filter
Preload
Shallow extensometer
Deep extensometer
Piezometers
-
8/20/2019 7. InSituTesting Website
32/38
Measurement of ground water pressure
Open standpipe piezometer
Piezometer
Schematic of open standpipe piezometer
installed in a borehole
-
8/20/2019 7. InSituTesting Website
33/38
Measurement of ground water pressure
Casagrande piezometer
Diagram of borehole with a
Casagrande piezometer
-
8/20/2019 7. InSituTesting Website
34/38
Measurement of ground water pressure
Driven-in piezometer
Cambridge driven-in
piezometer (Ater Parry, 1971)
-
8/20/2019 7. InSituTesting Website
35/38
Measurement of ground water pressure
-
8/20/2019 7. InSituTesting Website
36/38
Measurement of deformation
Inclinometer
Principal of Conventional Inclinometer Operation (After
Dunnicliff, 1988, 1993)
-
8/20/2019 7. InSituTesting Website
37/38
Measurement of deformation
Extensometer
Schematic of Probe Extensometer with Magnet/Reed
Switch Tansducer, Installed in a Borehole (After
Dunnicliff, 1988, 1993)
-
8/20/2019 7. InSituTesting Website
38/38
Measurement of deformation
Extensometer
Multiple Position Borehole Extensometer Installed from
Ground Surface