Use of SDMT results for engineering applications Workshop on Penetration Testing – University of Pisa, DESTEC Pisa – Italy, 9th 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) sara.amoroso@ingv.it

Outline of the presentation Flat dilatometer (DMT) Seismic dilatometer (SDMT) Interpretation of the parameters Engineering applications

Flat dilatometer (DMT) & Seismic DMT (SDMT)

DMT Flat dilatometer equipment BLADE FLEXIBLE MEMBRANE (D = 60mm)

DMT Test layout & components DMT blade Push rods Push force Pneumatic – electric cable Control box Gas tank Pneumatic cable p0 Lift-off pressure p1 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

(electrically insulated) DMT Working principle A B Sensing disk (electrically insulated) Sensing disk Retaining Ring Membrane 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

DMT Intermediate parameters DMT Readings Intermediate Parameters Id: Material Index P0 Kd: Horizontal Stress Index P1 Ed: Dilatometer Modulus

KD contains information on stress history σ’v (p0 - u0) D M T formula similar to K0: (p0 – u0)  σ’h KD is an “amplified” K0, because p0 is an “amplified” σh due to penetration p0 Very roughly KD ≈ 4K0 E.g. in NC K0 ≈ 0.5 and KD ≈ 2 KD well correlated to OCR and K0 (clay)

DMT Formulae – Interpreted parameters Intermediate Parameters Id Kd Ed 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

KD correlated to OCR (clay) = Kd 1.56 Marchetti 1980 (experimental) 0.5 Experimental Kamei & Iwasaki 1995 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 = NC OCR m OCR = 0.5 Kd 1.56 Using m  0.8 (Ladd 1977) and (Cu/’v)NC  0.22 (Mesri 1975) Cu = σ’v 0.5 Kd 1.25 0.22

DMT Formulae (1980 – today) Po and P1 Intermediate parameters Interpreted parameters

DMT results KD = 2  NC clay ID  M Cu   KD  soil type   KD  soil type (clay, silt, sand) common use shape similar to OCR helps understand history of deposit Generally dependable

Seismic dilatometer (SDMT)

Seismic Dilatometer (SDMT) Combination S + DMT 2 receivers VS determined from delay arrival of impulse from 1st to 2nd receiver (same hammer blow) Signal amplified + digitized at depth VS measured every 0.5 m DMT Marchetti 1980 SDMT Hepton 1988 ASTM D6635 – EC7 Martin & Mayne 1997,1998 ... TC16 2001

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 GO= ρ Vs2 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 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 G0 and MDMT SDMT data from 34 sites Data points tend to group according to soil type (ID) G0 /MDMT  constant, varies in wide range (≈ 0.5 to 20), especially in clay G0 /MDMT largely influenced by stress history (KD) By-product  rough estimates of VS (when not measured) Ratio G0 /MDMT vs. KD for various soil types (Marchetti et al. 2008, Monaco et al. 2009) MDMT, ID, KD (DMT)  G0  VS

Experimental interrelationship between G0 and MDMT COMMENTS Use of cu (or NSPT) alone as a substitute of VS (when not measured) for seismic classification of a site (Eurocode 8) does not appear founded on a firm basis If VS assumed as primary parameter for site classification, then a possible surrogate must be reasonably correlated to VS … But if 3 parameters (MDMT, ID, KD) barely sufficient to obtain rough estimates of VS, then estimating VS from only 1 parameter appears problematic …

Estimates of VS from DMT data Comparison of profiles of VS measured by SDMT and estimated from mechanical DMT data (Monaco et al. 2013)

Vs prediction from CPT and DMT DMT predictions of VS appear more reliable and consistent than the CPT predictions (Amoroso 2014) VS from DMT includes KD , sensitive to stress history, prestraining/aging and structure, scarcely detected by qc

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 G0 from VS working strain modulus GDMT from MDMT (track record DMT-predicted vs. measured settlements) But which  associated to GDMT ? ?

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/G0- curves in different soil types Range of values of GDMT/G0 and corresponding shear strain DMT determined by the "intersection" procedure in different soil types (Amoroso, Monaco, Lehane, Marchetti – Paper under review)

Tentative equation for deriving G/G0- curves from SDMT SDMT data points used to assist construction of hyperbolic equation DSDSS (Double Sample Direct Simple Shear tests): University of Roma La Sapienza Roio Piano – L'Aquila Comparison between G/G0 - decay curves obtained in Lab and estimated from SDMT by hyperbolic equation (Amoroso, Monaco, Lehane, Marchetti – Paper under review)

from SDMT (under study) 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

from SDMT (under study) Validation of in situ G- decay curves from SDMT (under study) HSS model – PLAXIS Assumptions: G/G0 = 0.722 γ0.7

from SDMT (under study) 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”

Concluding remarks At sites where VS has not been measured and only mechanical DMT results from past investigations are available, rough estimates of VS (via G0) 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 (G0 from VS) and a working strain modulus GDMT (obtained from MDMT derived by usual DMT interpretation) Use of proposed hyperbolic relationship, which requires to input ratio GDMT/G0 + presumed "typical" shear strain DMT for a given soil type, can provide a useful first order estimate of G/G0 - curves from SDMT (further validation needed)

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