Transcript DMT
Workshop on Penetration Testing – University of Pisa, DESTEC Pisa – Italy, 9 th October 2014
Flat dilatometer (DMT) & Seismic DMT (SDMT) Use of SDMT results for engineering applications Sara Amoroso
(Istituto Nazionale di Geofisica e Vulcanologia, L’Aquila, Italy) [email protected]
Outline of the presentation 1.
Flat dilatometer (DMT) 2.
Seismic dilatometer (SDMT) 3.
Interpretation of the parameters 4.
Engineering applications
Flat dilatometer (DMT) & Seismic DMT (SDMT)
DMT Flat dilatometer equipment
BLADE FLEXIBLE MEMBRANE (D = 60mm)
DMT Test layout & components
Pneumatic – electric cable Control box Push force Pneumatic cable Gas tank Push rods DMT blade p 0 Lift-off pressure p 1 Pressure for 1.1 mm expansion Measurements performed after penetration independent from insertion method
DMT insertion with penetrometer
Most efficient method: direct push with penetrometer
DMT Working principle
Sensing disk (electrically insulated) Sensing disk A B Blade is like an electrical switch, can be off or on NO ELECTRONICS no zero drift, no temperature effects Nothing that the operator can regulate, adjust, manipulate Retaining Ring Membrane
DMT Intermediate parameters DMT Readings Intermediate Parameters P 0 P 1 Id
: Material Index
Kd
: Horizontal Stress Index
Ed
: Dilatometer Modulus
K D contains information on stress history
D M T K D = (p 0 - u σ’ v 0 ) formula similar to K 0 : (p 0 – u 0 ) σ’ h p 0 K D is an “amplified” K 0 , because p 0 is an “amplified” σ h due to penetration Very roughly K D ≈ 4K 0 E.g. in NC K 0 ≈ 0.5 and K D ≈ 2 K D well correlated to OCR and K 0 (clay)
DMT Formulae – Interpreted parameters Intermediate Parameters Id Ed Kd Interpreted Parameters M: Constrained Modulus Cu: Undrained Shear Strength Ko: Earth Pressure Coeff (clay) OCR: Overconsolidation ratio (clay)
: Safe floor friction angle (sand)
: Unit weight and description
K D correlated to OCR (clay) OCR = 0.5
K d 1.56
Experimental Kamei & Iwasaki 1995 Marchetti 1980 (experimental) Theoretical Finno 1993 Theoretical Yu 2004
Cu correlation from OCR Ladd SHANSEP 77 (SOA TOKYO) Ladd: best Cu measurement not from TRX UU !!
best Cu from oed
OCR
Shansep
Cu σ’ v OC = Cu σ’ v NC OCR m OCR = 0.5
K d 1.56
Using m 0.8 (Ladd 1977) and (Cu/ ’ v ) NC 0.22 (Mesri 1975) Cu = 0.22
σ’ v 0.5 K d 1.25
Po and P1 Intermediate parameters
DMT Formulae (1980 – today)
Interpreted parameters
DMT results I D
soil type (clay, silt, sand)
M
Cu
common use Generally dependable K D = 2 NC clay shape similar to helps understand OCR history
K D
of deposit
Seismic dilatometer (SDMT)
Seismic Dilatometer (SDMT)
Combination S + DMT 2 receivers V S determined from delay arrival of impulse from 1st to 2nd receiver (same hammer blow) Signal amplified + digitized at depth V S measured every 0.5 m DMT Marchetti 1980 ASTM D6635 – EC7 TC16 2001 SDMT Hepton 1988 Martin & Mayne 1997,1998 ...
Hammer for shear wave
Example seismograms SDMT at Fucino
Delay well conditioned from Cross Correlation coeff of variation of Vs 1-2 %
SDMT results High repeatability G O = ρ Vs 2 DMT Seismic DMT
Vs at National Site FUCINO – ITALY SDMT (2004) SCPT Cross Hole SASW AGI (1991) Fucino-Telespazio
National Research Site (Italy) 2004 20
Standards EUROCODE 7 (1997 and 2007).
Standard Test Method, European Committee for Standardization, Part 2: Ground investigation and testing, Section 4. Field tests in soil and rock. 4.10. Flat Dilatometer Test (DMT).
ASTM (2002 and 2007).
Standard Test Method D6635-01, American Society for Testing and Materials. The standard test method for performing the Flat Dilatometer Test (DMT), 14 pp.
TC16 (1997).
“The DMT in soil Investigations”, a report by the ISSMGE Technical Committee tc16 on Ground Property, Characterization from in-situ testing, 41 pp.
ASTM (2011)
– Standard Test Method D7400 – 08, “Standard Test Methods for Downhole Seismic Testing “, 11 pp.
PROTEZIONE CIVILE Gruppo di lavoro (2008)
– Indirizzi e criteri per la microzonazione sismica. Prova DMT pp. 391-397, Prova SDMT pp. 397-405
Consiglio Superiore dei Lavori Pubblici (2008)
– Istruzioni per l'applicazione Norme Tecniche per le Costruzioni NTC08. Circolare 02/02/09 , paragrafo C6.2.2
Use of SDMT results for engineering applications
Experimental interrelationship between G 0 and M DMT
SDMT data from 34 sites ● Data points tend to group according to soil type (I D ) ● G 0 /M DMT constant, varies in wide range (≈ 0.5 to 20), especially in clay ● G 0 /M DMT largely influenced by stress history (K D ) ● By-product estimates of V S rough (when not measured) Ratio
G 0
/
M DMT
vs.
K D
for various soil types (Marchetti et al. 2008, Monaco et al. 2009) M DMT , I D , K D (DMT) G 0
V S
Experimental interrelationship between G 0 and M DMT
COMMENTS Use of
c u
firm basis (or
N SPT
) alone as a substitute of
V S
(when not measured) for seismic classification of a site (Eurocode 8) does not appear founded on a If
V S
assumed as primary parameter for site classification, then a possible surrogate must be reasonably correlated to
V S
… But if 3 parameters (M DMT , I D , K D ) barely sufficient to obtain rough estimates of
V S
, then estimating
V S
from only 1 parameter appears problematic …
Estimates of V S from DMT data
Comparison of profiles of V S measured by SDMT and
estimated
from mechanical DMT data (Monaco et al. 2013)
Vs prediction from CPT and DMT
DMT predictions of
V S
appear more reliable and consistent than the CPT predictions (Amoroso 2014)
V S
from DMT includes
K D
, sensitive to stress history, prestraining/aging and structure, scarcely detected by
q c
Main SDMT applications
Settlements of shallow foundations Compaction control Slip surface detection in OC clay Quantify σ' h relaxation behind a landslide Laterally loaded piles Diaphragm walls FEM input parameters Liquefiability evaluation
In situ G γ decay curves
…
Tentative method for deriving in situ
G
decay curves from SDMT SDMT
small strain
modulus
working strain G 0
modulus from V
G DMT S
from M
DMT
(track record DMT-predicted vs. measured settlements)
But which
associated to G DMT ?
?
Shear strain "
DMT
" Quantitative indications by comparing at various test sites and in different soil types
SDMT data
+ “
reference
”
stiffness decay curves
: back-figured from the observed behavior under a full-scale test embankment (Treporti) or footings (Texas) obtained by laboratory tests (L'Aquila, Emilia Romagna, Fucino) reconstructed by combining different in situ/laboratory techniques (Western Australia)
same-depth "reference" stiffness decay curve
Typical ranges of
DMT in different soil types
"Typical shape" G/G 0 curves in different soil types (Amoroso, Monaco, Lehane, Marchetti – Paper under review) Range of values of G DMT /G 0 and corresponding shear strain DMT determined by the "intersection" procedure in different soil types
Tentative equation for deriving
G/G
0
curves from SDMT
SDMT data points used to assist construction of hyperbolic equation
G G
0 1
G
0
G DMT
1 1
DMT
Roio Piano – L'Aquila Comparison between G/G 0 decay curves obtained in Lab and estimated from SDMT by hyperbolic equation
DSDSS (Double Sample Direct Simple Shear tests): University of Roma La Sapienza
(Amoroso, Monaco, Lehane, Marchetti – Paper under review)
Validation of in situ G
decay curves from SDMT (under study)
Comparison between HSS model – PLAXIS from SDMT parameters and monitoring activities for the excavation of Verge de Montserrat Station (Barcelona, Spain) Working group: Amoroso, Arroyo, Gens, Monaco, Di Mariano
5 10 15 20 25 30 35 40 45 Validation of in situ G
decay curves from SDMT (under study)
0 0
Oedometric modulus Eoed (MPa)
20 40 60 80 100
HSS model – PLAXIS
Eoed from SDMT (Eoed=Mdmt) Eoed from HSS model (PLAXIS)
G
0
G
0
ref
1 '
p ref
m
Assumptions:
M DMT
E oed
E
50
E ur
/ 4 1.2
VERGE MONTSERRAT UG4 Sand
GDMT/G0 Hyperbolic curve 1 0.8
0.6
0.4
G/G 0 = 0.722
0.2
0 1.00E-04 1.00E-03
γ 0.7
1.00E-02 1.00E-01
shear strain, γ (%)
1.00E+00 1.00E+01
Validation of in situ G
decay curves from SDMT (under study)
Preliminary results show an acceptable agreement between experimental data (monitoring activities) and numerical analysis (based on SDMT data)
Phase 9 “Pumping down to a depth of 10 m”
-10
Diaphragm wall horizontal movement (mm)
-5 0 5 0 5 10 15 20 25 30 35 40 O BSERVED N UMERICAL A NALYSIS 10
Concluding remarks
At sites where
V S
has not been measured and only mechanical DMT results from past investigations are available, rough estimates of
V S
(via
G 0
) can be obtained from mechanical DMT data SDMT results could be used to assess the decay of in situ stiffness with strain level and to provide guidance in selecting
G
curves
in various soil types, thanks to its ability to provide both a small strain modulus (
G 0
from
V S
) and a working strain modulus
G DMT
derived by usual DMT interpretation) (obtained from M DMT Use of proposed hyperbolic relationship, which requires to input ratio
G DMT
/
G 0
+ presumed "typical" shear strain
DMT
for a given soil type, can provide a useful first order estimate of
G
/
G 0
curves from SDMT (further validation needed)