The Flat Dilatometer Test (DMT):Design Applications

and Recent Developments

P. Monaco, S. Marchetti & G. TotaniUniversity of L'Aquila, Italy

ORIGINAL PAPERMARCHETTI S. (1980). In Situ Tests by Flat Dilatometer.J. Geotech. Engrg. Div. ASCE, 106(GT3), 299-321

STANDARDSASTM D6635-01 (2001). Standard Test Method for Performing the Flat Plate Dilatometer.EUROCODE 7 – Geotechnical Design – Part 2: Ground Investigation and Testing. EN 1997-2:2007

SOA REPORTTC16 (2001). The Flat Dilatometer Test (DMT) in Soil Investigations. May 2001, 41 pp. Reprint in Proc. 2nd Int. Conf. on Flat Dilatometer, Washington D.C., 7-48

INTERNETwww.marchetti-dmt.it biblio site (download papers)

KEY DMT REFERENCES

BLADE

FLAT DILATOMETER (DMT)

FLEXIBLE MEMBRAN

E

Push force provided by penetrometer or drill rig

DMT blade Push rods (e.g. CPT) Pneumatic-electrical cable Control unit Pneumatic cable Gas tank MEMBRANE EXPANSION

GENERAL LAYOUT of DMT

p0 & p1 readings at 20 cm depth intervals

CLAY, SILT, SAND – But can cross through GRAVEL layers 0.5 m

Soils from VERY SOFT to VERY STIFF (upper limit is push capacity of rig)

Clays: Cu = 2-4 to 1000 kPa (marls)

Moduli: up to 400 MPa

SOILS that can be TESTED by DMT

Basic DMT reduction formulae (TC16 2001)

p0 Corrected First Reading p0 = 1.05 (A - ZM + A) - 0.05 (B - ZM - B) p1 Corrected Second Reading p1 = B - ZM - B ID Material Index ID = (p1 - p0) / (p0 - u0) KD Horizontal Stress Index KD = (p0 - u0) / 'v0 ED Dilatometer Modulus ED = 34.7 (p1 - p0) K0 Coeff. Earth Pressure in Situ K0,DMT = (KD / 1.5)0.47 - 0.6

OCR Overconsolidation Ratio OCRDMT = (0.5 KD)1.56 cu Undrained Shear Strength cu,DMT = 0.22 'v0 (0.5 KD)1.25 Friction Angle safe,DMT = 28° + 14.6° log KD - 2.1° log2

KD ch Coefficient of Consolidation ch,DMTA 7 cm2

/ tflex kh Coefficient of Permeability kh = ch w / Mh (Mh K0 MDMT) Unit Weight and Description (see chart in TC16 2001)

MDMT = RM ED if ID 0.6 RM = 0.14 + 2.36 log KD if ID 3 RM = 0.5 + 2 log KD if 0.6 < ID < 3 RM = RM,0 + (2.5 - RM,0) log KD

with RM,0 = 0.14 + 0.15 (ID - 0.6) if KD > 10 RM = 0.32 + 2.18 log KD

M Vertical Drained Constrained Modulus

if RM < 0.85 set RM = 0.85 u0 Equilibrium Pore Pressure u0 = p2 = C - ZM + A

DMT results

KD = 2 NC clay

ID

M Cu

KD

soil type(clay, silt,

sand)

common use shape similar to OCR helps understand history of deposit

In most cases DMT used to determine common geotechnical design parameters

Experience has shown undrained shear strength Cu and constrained modulus M by DMT generally accurate and dependable for design

Comparisons at several research sites indicate quite good agreement between profiles of Cu and M by DMT and reference values by other tests ( see TC16 2001)

Design using soil parameters

Comparisons Cu DMT vs. Cu reference

Research Site Bothkennar

(UK)

Research SiteFucino (Italy)

AGI (1991)

Nash et al. (1992)

M (MPa)

0

10

20

30

0 20 40 60 80

z (m

)

M by DMT vs. M by high quality oedometersOnsøy (Norway)

Comparisons MDMT vs. Mreference

Lacasse (1986)

MDMT

M back-calculated

M by DMT vs. M back-calculated from local vertical strains measured under Treporti full-scale test embankment (Italy)

Marchetti et al. (2006)

by Boussinesq

Settlement predictionNo. 1 DMT application

Classic linear elastic 1-D approach – or 3-D with E 0.8 MDMT (similar predictions)

Settlement under working loads (Fs 2.5-3.5)

0

50

100

150

200

250

300

350

400

0 50 100 150 200 250 300 350 400

DMT-calculated settlement (mm)

Me

as

ure

d s

ett

lem

en

t (m

m)

Hayes 1990 Skiles & Townsend 1994 Marchetti 1997 Didaskalou 1999 Marchetti et al. 2004 Mayne 2005

DMT/measured=0.5

DMT/measured=2

DMT/measured=1ALL SOILS

0

50

100

150

200

250

300

350

400

0 50 100 150 200 250 300 350 400

DMT-calculated settlement (mm)

Me

as

ure

d s

ett

lem

en

t (m

m)

Hayes 1990 Skiles & Townsend 1994 Marchetti 1997 Didaskalou 1999 Marchetti et al. 2004 Mayne 2005

DMT/measured=0.5

DMT/measured=2

DMT/measured=1ALL SOILS

Summary of comparisonsDMT-predicted vs. observed settlements

Monaco et al. (2006)

Large No. of case histories good agreement for wide range of soil types, settlements, footing sizes

Average ratio DMT-calculated/observed settlement 1.3

Band amplitude (ratio max/min) < 2 i.e. observed settlement within ± 50

% from DMT-predicted

Experience suggests DMT well suited to detect BENEFITS of SOIL IMPROVEMENT due to its high sensitivity to changes of stresses/density in soil

Several comparisons of CPT and DMT before/after compactionSchmertmann et al. (1986), Jendeby (1992) increase in MDMT after compaction of sand 2 increase in qc (CPT)Pasqualini & Rosi (1993) ...

Compaction control

Ratio MDMT /qc before/after compaction of a loose sand fill (Jendeby 1992)

DMT vs. CPT before/after compaction BEFORE AFTERBEFORE AFTERBEFORE AFTER MDMT

MDMTqcqc

DMT-KD method Verify if an OC clay slope contains ACTIVE (or old QUIESCENT) SLIP SURFACES(Totani et al. 1997)

0 2

10

20

30

D

1. SLIDING

K (DMT) 2

3. RECONSOLIDATION(NC STATE)

4. INSPECT D PROFILEK

2. REMOULDING

Detecting slip surfaces in clay slopes

LANDSLIDE "FILIPPONE" (Chieti)

LANDSLIDE "CAVE VECCHIE" (S. Barbara)

DOCUMENTED SLIP SURFACE

DOCUMENTED SLIP SURFACE(inclinometers)

Validation of DMT-KD method

DMT for LIQUEFACTION Correlations for evaluating Cyclic

Resistance Ratio CRR from KD developed in past 2 decades, stimulated by:

Key element supporting well-based CRR-KD correlation: ability of KD to reflect aging in sands (1st order of magnitude influence on liquefaction) + sensitivity of KD to non-textbook OCR crusts in sands

– Sensitivity of KD to factors known to increase liquefaction resistance: Stress History, prestraining/aging, cementation, structure …

– Correlation KD – Relative Density

– Correlation KD – In situ State Parameter

Summary + latest version CRR-KD correlation see Monaco et al. (2005 ICSMGE Osaka)

Magnitude M = 7.5 – Clean sand

0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10

KD

CSRor

CRR

Robertson & Campanella 1986

Marchetti 1982

M = 7.5

NO LIQUEFACTION

LIQUEFACTION

Reyna & Chameau 1991

Range of curves derived from CPT

Range of curves derived from SPT

New tentativeCRR-KD curveMonaco et al. 2005

0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10

0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10

KD

CSRor

CRR

Robertson & Campanella 1986

Marchetti 1982

M = 7.5

NO LIQUEFACTION

LIQUEFACTION

Reyna & Chameau 1991

Range of curves derived from CPTRange of curves derived from CPT

Range of curves derived from SPTRange of curves derived from SPT

New tentativeCRR-KD curveMonaco et al. 2005

New tentativeCRR-KD curveMonaco et al. 2005

Curves for evaluating CRR from KD

(Seed & Idriss 1971 simplified procedure)

DMT for DESIGN ofLATERALLY LOADED PILES

Robertson et al. (1987)Marchetti et al. (1991)

2 methods recommended for deriving P-y curves for laterally loaded piles from DMT (single pile, 1st time monotonic loading)

Mortaiolo (Italy)

NC soft clay

Mortaiolo (Italy)

NC soft clay

Independent validations 2 methods provide similar predictions, in very good agreement with observed full-scale pile behaviour

DMT for DESIGN ofDIAPHRAGM WALLS

Tentative correlation for deriving the coefficient of subgrade reaction Kh for design of multi-propped diaphragm walls from MDMT

Indications on how to select input moduli for FEM analyses (PLAXIS Hardening Soil model) based on MDMT

g.l.

sH

L

g.l.g.l.

ssHH

LL

Monaco & Marchetti (2004 – ISC'2 Porto)

Subgrade compaction control

MDMT acceptance profile(max always found at 25-26

cm)

Bangladesh Subgrade Compaction Case History90 km Road Rehabilitation Project

Acceptance MDMT profile fixed and used as alternative/fast acceptance tool for quality control of subgrade compaction, with only occasional verifications by originally specified methods (Proctor, CBR, plate)

• 2 receivers spaced 0.5 m

• 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

Combination S +

DMT

Seismic Dilatometer (SDMT)

Hepton 1988Martin & Mayne 1997, 1998 ... (Georgia Tech, USA)

Validation of Vs by SDMT

Comparison of Vs profiles by SDMTand by other tests

Fucino research site(Italy)

SDMT (2004)

AGI (1991)

SCPT Cross Hole SASW

Vs (m/s)

SHEAR WAVEVELOCITY

SDMT results

SDMT profiles at the site of Fiumicino (Italy)

SDMT accurate and highly repeatable Vs (in addition to usual DMT results)

SDMT small strain modulus G0 from Vsworking strain modulus MDMT

(settlements) Tentative methods to derive in situ G- curves by

SDMT Two points help in selecting the G- curve

In situ G- decay curves by SDMT

Mayne (2001)Ishihara (2001)

HARA (1973) YOKOTA et al. (1981) TATSUOKA (1977) SEED & IDRISS (1970) ATHANASOPOULOS (1995) CARRUBBA & MAUGERI (1988)

0.05 to 0.1%

HARA (1973) YOKOTA et al. (1981) TATSUOKA (1977) SEED & IDRISS (1970) ATHANASOPOULOS (1995) CARRUBBA & MAUGERI (1988)

0.05 – 0.1 %

Maugeri (1995)

SDMT 2 parallel independent evaluations of CRR from VS e KD

(Seed & Idriss 1971 simplified procedure)

SDMT for LIQUEFACTION

Andrus & Stokoe (2000)Andrus et al. (2004)

Monaco et al. (2005)ICSMGE Osaka

CRR from Vs CRR from KD

DMT quick, simple, economical, highly reproducible in situ test

Executable with a variety of field equipment

Dependable estimates of various design parameters/information

– soil type– stress state/history– constrained modulus M– undrained shear strength Cu in clay– consolidation/flow parameters– ...

FINAL REMARKS

Variety of design applications

Most effective vs. common penetration tests when settlements/deformations important for design (e.g. strict specs or need to decide: piles or shallow ?)

SDMT accurate measurements of Vs (and G0) + usual DMT results – greatly enhances DMT capability

FINAL REMARKS

Special thanks to Allan McConnell (IGS)