1. Short Course on the DMT Paola Monaco 2nd International Conference on
the Flat Dilatometer Washington, D.C. - April 2 – 5, 2006
Short Course on the DMT
LATERALLY LOADED PILES
MULTI-ANCHORED DIAPHRAGM WALLS
SLOPE STABILITY
LIQUEFACTION
Paola Monaco
University of L'Aquila, Italy

2. LATERALLY LOADED PILES
DMT for DESIGN of
LATERALLY LOADED PILES

3. Background
Original stimulus for development of DMT  tool for parameters for DESIGN of LATERALLY LOADED PILES
Similarity DMT – LL PILES
Structural element installed in soil
LATERAL deformation
MARCHETTI (1977) - "Devices for In Situ Determination of Soil Modulus Es" Proc. 9th ICSMFE, Tokyo, Spec. Session No. 10.

4. Recommended methods for
P-y curves from DMT
ROBERTSON et al. (1987) - clays and sands
Adaptation of early P-y curve methods (Skempton 50 - Matlock 1970 cubic parabola approach) with "lab soil properties" inferred from DMT
MARCHETTI et al. (1991) - clays
Straightforward procedure deriving P-y curves DIRECTLY from DMT - bypassing tortuous step of estimating "lab soil properties" by DMT
Both for SINGLE PILE & 1st time monotonic loading
ROBERTSON et al. (1987) - "Design of Laterally Loaded Driven Piles Using the Flat Dilatometer". Geot. Testing Jnl, No. 1.
MARCHETTI et al. (1991) - "P-y curves from DMT data for piles driven in clay". Proc. 4th Int. DFI Conf. Piling and Deep Foundations, Stresa, Vol. 1.

5. Method by Marchetti et al. (1991)Pu
Esi
P-y CURVE at given depth
Pu = f(p0 - u0)  shear strength
Esi = f(ED)  stiffness
Pu =   K1  (p0 - u0 )  D ultimate lateral soil resistance
Esi =   K2  ED initial tangent "soil modulus"
reduction factor for z < 7 D
( = 1 for z = 7 D)
K1 = empirical soil resistance coefficient
K2 = 10  (D / 0.5 m) empirical soil stiffness coefficient

6. Validations on full scale piles
Mortaiolo (Italy)
NC soft clay
Marchetti et al. (1991) + NGI (1998), Georgia Tech (1998)
2 methods  similar predictions
Very good agreement PREDICTED vs OBSERVED behavior

7. Laterally loaded pile groups
Ruesta & Townsend (1997)
P-y curves derived from DMT/PMT, based on large-scale load test on 16 pile group
RUESTA & TOWNSEND (1997) - "Evaluation of Laterally Loaded Pile Group at Roosvelt Bridge". Jnl ASCE GGE, 123, 12.

8. DMT for DESIGN of
MULTI-ANCHORED
DIAPHRAGM WALLS

9. Background
Multi-anchored diaphragm walls widely used today for retaining deep open pit excavations (e.g. car parkings), often in combination with top-down construction
"SPRING" calculations (Subgrade Reaction Method SRM) still currently used in design practice
CRUCIAL STEP  selection of coefficient of subgrade reaction Kh – depends on soil modulus + "geometrical-mechanical" factors ???
Yet engineers familiar with moduli, not with Kh
Useful even crude RELATIONS M to Kh

10. Existing Kh formulations
for diaphragm walls
Existing formulations for Kh (Balay 1984, Becci & Nova 1987 etc.) generally
Kh  E/B
with B = "characteristic dimension"  width of soil zone "loaded" by diaphragm wall
Indications for B generally for cantilever walls (e.g. B  free height or embedded depth)
For multi-restrained walls estimate of B >> uncertain (earth pressure  K0 , displacements limited by restraints)

11. Tentative correlation Kh – MDMT
Monaco & Marchetti (2004) - ISC'2 Porto
FEM analysis (PLAXIS) with input soil moduli estimated from MDMT – various cases of wall/soil stiffness, excavation depth and prop spacing
SPRING analysis varying Kh until bending moments and horizontal displacements of wall  values calculated by FEM
Tentative correlation between "best fit" Kh (best match of FEM results) and MDMT
Kh calibrated vs FEM = assumed as "REALITY"
NUMERICAL study (no comparisons predicted/ observed behavior in real cases) – needs validation

12. Selection of Plaxis input moduli
based on DMT moduli
Hardening Soil Model
3 moduli at pref = 100 kPa:
1-D tangent modulus Eoedref
Triaxial modulus E50ref
Unloading-reloading modulus Eurref
Eoed = Eoedref ('1 /pref ) m
E50 = E50ref ('3 /pref ) m m  0.5-1
Eur = Eurref ('3 /pref ) m

13. Eurref = 4 Eoedref (Vermeer 2001)
Schanz & Vermeer (1997)
Literature survey for very loose to very dense quartz sands: E50ref = 15 to 75 MPa  MDMT for sands of similar densities
E50ref correlated to Eoedref  E50 triax can be estimated from Eoed
All moduli required by HS Model estimated from MDMT ("operative")
Eoed = MDMT
E50ref = Eoedref
Eurref = 4 Eoedref (Vermeer 2001)

14. Input soil data – HS Model
 = 19 kN/m3
' = 30°
c' = 0.5 kPa
 = 0
 = 20° (wall/soil)
K0 = 0.5
Eoedref = MDMT at pref = 100 kPa
SOFT SOIL Eoedref = 4 MPa
MEDIUM SOIL Eoedref = 16 MPa
STIFF SOIL Eoedref = 40 MPa
E50ref = Eoedref Eurref = 4 Eoedref
m = ur = 0.2
3 soils differ only for STIFFNESS
For all soils E50 /Eoed /Eur = 1/1/4
All other parameters equal
Drained conditions (u = 0 everywhere)
Wall "wished in place"

15. Input diaphragm wall data
H = m
s = 3-6 m
L = 6 m
g.l. H
Rigid wall
EI = 2083 MNm2/m
(1 m thick concrete wall)
Flexible wall
EI = 232 MNm2/m
(steel sheetpile wall) s L
Top-down excavation
Prop installation
Excavation down to next prop
Prop installation ...

16. Comparison FEM vs SRM
EARTH PRESSURE
DISPLACEMENT
BENDING MOMENT
DEPTH
Example of results for soft soil/flexible wall, excavation depth H = 18 m, prop spacing s = 3 m

17. "Best fit" Kh vs excavation depth
Excavation depth H (m)
Kh (kN/m3)
MDMT = 5-7 MPa
MDMT = MPa
MDMT = MPa
1 m thick concrete diaphragm wall
s = 3 m
s = 6 m

18. Tentative correlation Kh – MDMT Kh = MDMT/B
Kh decreases when WALL DEFORMATIONS increase due to >> EXCAVATION DEPTH or << RESTRAINT DEGREE
Hence increase in B = width of soil zone involved by wall movements  "characteristic length"
Kh = MDMT/B
(similar to existing formulations for Kh )
Broad indication for selecting design values of B – hence Kh – for multi-propped diaphragm walls in cases of similar wall geometry/stiffness and prop spacing for various ranges of MDMT

19. B values in the formula Kh = MDMT/B
MDMT = 5-7 MPa
s = 3 m
Excavation depth H (m)
B (m)
s = 6 m
s = prop spacing
1 m thick concrete diaphragm wall

20. B values in the formula Kh = MDMT/B
MDMT = MPa
s = 3 m
Excavation depth H (m)
B (m)
s = 6 m
s = prop spacing
1 m thick concrete diaphragm wall

21. B values in the formula Kh = MDMT/B
1 m thick concrete diaphragm wall
MDMT = MPa
s = 3 m
Excavation depth H (m)
B (m)
s = 6 m
s = prop spacing

22. DMT for EVALUATING
STABILITY of a SLOPE

23. Verify if an OC clay slope contains ACTIVE (or old QUIESCENT) SLIP SURFACES

24. DMT-KD method for detecting slip surfaces in OC clay slopes
Identifying zones of NC clay in a slope which, otherwise, exhibits an OC profile, using KD  2 as identifier of NC zones
Specific value KD = 2 (not simply "weak zones")
Detects even quiescent slip surfaces which could reactivate (inclinometers cannot – must move)
But cannot establish if slope is presently moving and how fast (inclinometers can)
In many cases DMT + inclinometers helpfully used in combination (e.g. use KD profiles to optimize location/depth of inclinometers)

25. Examples of KD  2 in slip surfaces
LANDSLIDE "FILIPPONE" (Chieti)
DOCUMENTED SLIP SURFACE
LANDSLIDE "CAVE VECCHIE" (S. Barbara)
DOCUMENTED SLIP SURFACE

26. Todi Hill landslide (Italy)
Qualitative reconstruction (Tonnetti 1978)
KD  2 layers correspond to SLIP SURFACES by INCLINOMETERS

27. Chieti Hill (Italy)
Problem: SAFETY of very heavy NEW BUILDING to be constructed on an OC CLAY SLOPE
Slope stable ???
Attacked by verifying via KD presence of previous slip surfaces
DMT tests
Central part "infected" by KD  2 layers = past/present shear planes
sound clay

28. Solution: MODIFY original PROJECT to increase safety of building

29. LEROUEIL (2001) - Rankine Lecture
Géothecnique 51(3),

30. DMT for EVALUATING
SAND LIQUEFIABILITY

31. Background
Many of factors making DMT + sensitive to compaction and + accurate for settlements (Stress History ...) are known to affect "liquefiability"
Correlations CRR-KD have been developed in last two decades, stimulated by recognized sensitivity of KD to factors known to increase liquefaction resistance – stress state/history ...
Reference approach  simplified procedure (Seed & Idriss 1971)

32. Simplified procedure (Seed & Idriss 1971)
LIQUEFACTION if seismic stress CSR  liquefaction resistance of soil CRR
CSR = av / 'vo = 0.65 (amax / g ) (vo / 'vo ) rd
CRR from CPT, SPT, VS … (case histories)
Youd & Idriss (2001) – ASCE Jnl GGE 127(4)
Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils

33. Recommended CRR curves for CPT-SPT
CPT Clean Sand Base Curve
CSR or CRR
CSR or CRR
SPT Clean Sand Base Curve
Corrected CPT Tip Resistance qc1N
qc1N = (pa /'vo ) n (qc /pa )
Youd & Idriss (2001)
Summary Report 1996 & 1998 NCEER Workshops – ASCE Jnl GGE 127(4)
Corrected SPT Blow Count (N1) 60
(N1) 60 = Nm CN CE CB CR CS

34. Recommended CRR-VS curves
CSR or
CRR
Andrus & Stokoe (2000)
Andrus et al. (2004)
Stress-Corrected Shear Wave Velocity VS1 (m/s)
VS1 = VS ( pa /'vo ) 0.25

35. Evaluation of CRR from Lab / CC
Major obstacle is obtaining UNDISTURBED samples, unless by non-routine sampling techniques (e.g. ground freezing)
Adequacy of using RECONSTITUTED sand specimens – even "exactly" at the same "in situ density" – is questionable (in situ fabric / cementation / aging affect significantly CRR)

36. Importance of evaluating CRR
by more than one method
Robertson & Wride (1998)  CRR by CPT (preferred to SPT, due to its poor repeatability) adequate for low-risk small-scale projects, for medium- to high-risk projects recommended to estimate CRR by more than one method
NCEER Workshops (Youd & Idriss 2001)  if possible two or more tests should be used for a more reliable evaluation of CRR
Idriss & Boulanger (2004)  often synthesis of findings from several different procedures provides most insight ... using a number of in situ testing methods should continue to be the basis for standard practice, and the allure of relying on a single approach (e.g. CPT-only) should be avoided

37. Basis of the correlation CRR-KD
KD = ( po - uo ) / 'vo
Horizontal Stress Index
Research has shown KD reactive to factors increasing CRR: in situ stress state, stress-strain history, structure, cementation, aging …  KD index parameter of liquefaction resistance
Impossible to isolate each contribution, however a low KD signals none of above factors is high, i.e. sand is loose, uncemented, in a low K0 environment and has little stress history  under these conditions may liquefy or develop large strains under cyclic loading

38. Basis of the correlation CRR-KD
Confirmation from recent studies:
- Sensitivity of KD in monitoring densification
- Sensitivity of KD to prestraining
- Correlation KD - Relative Density
- Correlation KD - in situ State Parameter

39. Sensitivity of DMT in monitoring
soil densification
High sensitivity of DMT in monitoring DENSIFICATION, demonstrated by several studies, suggests DMT may also sense SAND LIQUEFIABILITY
A liquefiable sand may be regarded as a sort of "negatively compacted" sand
Plausible that DMT sensitivity holds both in positive and negative range

40. Sensitivity of KD to prestraining
(prestraining cycles)
CC TEST N. 216 IN TICINO SAND
Jamiolkowski & Lo Presti ISC'98 Atlanta
KD %
qD %
Increase in KD caused by prestraining found  3 to 7 times increase in penetration resistance qD

41. Importance of stress-strain history
Jamiolkowski et al. (1985)  reliable predictions of liquefaction resistance of sand deposits of complex stress-strain history require development of some new in situ device (other than CPT or SPT), more sensitive to effects of past stress-strain histories

42. Correlation KD - DR (NC uncemented sands)
Relative Density DR (%) KD
Reyna & Chameau (1991)
Additional KD - DR datapoints obtained by Tanaka & Tanaka (1998) on high quality frozen samples

43. Example of "KD crusts" in sands - Catania
"Crust-like" KD profiles – very similar to typical KD profiles in OC desiccation crusts in clay – found at top of most sand deposits investigated by DMT
KD profile generally reflects OCR in sand – often result of complex history of preloading / desiccation / other effects
Shallow KD crusts may be also due (in part) to dilatancy
In shallow KD crusts in most sandy sites KD >> (giving DR = 100 % by Reyna & Chameau KD -DR correlation for NC uncemented sands)  part of KD due to overconsolidation or cementation, rather than to DR

44. Example of "KD crusts" in sands - Catania
MATERIAL
INDEX
CONSTRAINED
MODULUS
UNDRAINED
SHEAR STRENGTH
HORIZONTAL
STRESS INDEX
SHEAR WAVE
VELOCITY
CLAY SILT SAND

45. Importance of OCR/aging
Pyke (2003) (Discussion to Youd et al. 2001, ASCE Jnl GGE)
Seed (1979) listed various factors assumed to have similar effect on penetration resistance and liquefaction potential, but these were never intended to be equalities
Two of these factors – overconsolidation and aging – likely to have much greater effect on increasing liquefaction resistance than penetration resistance
Soils even lightly OC or more than several decades old may have greater resistance to liquefaction than indicated by current correlations, which are heavily weighted by data from hydraulic fills and very recent streambed deposits

46. CRR from State Parameter
SP important step forward in characterizing soil behavior, combining effects of both DR and stress level in a rational way
SP (vertical distance between current state and critical state line in e - ln p' plot) governs tendency of a sand to increase or decrease in volume when sheared, hence it is strongly related to liquefaction resistance
More rational methods for evaluating CRR would make use of SP (e.g. Boulanger 2003, Boulanger & Idriss 2003)
Recent research supports KD as an index reflecting SP

47. Correlation KD – State Parameter
KD / K0
In situ state parameter 0
Yu (2004) – Mitchell Lecture, ISC'2 Porto

48. Physical meaning of KD
Reaction of soil against penetrating blade could be seen as indicator of soil reluctance to volume reduction
A loose collapsible soil will not strongly contrast a volume reduction and will oppose a low 'h (hence a low KD) to blade insertion
Moreover such reluctance is determined at existing ambient stresses increasing with depth (apart alteration of stress pattern close to blade)
At least intuitively, a connection is expectable between KD and SP

49. Previous CRR-KD curves
0.5
0.4
0.3
0.2
0.1
M = 7.5
Reyna & Chameau 1991
CSR or
CRR
LIQUEFACTION
Marchetti 1982
Robertson & Campanella 1986
NO LIQUEFACTION KD

50. New tentative CRR-KD curve
Monaco et al. (2005)  new tentative correlation for evaluating CRR from KD – to be used according to the Seed & Idriss (1971) "simplified procedure"
New correlation combines previous CRR-KD curves + "experience" incorporated in current methods based on CPT-SPT, translated using DR as intermediate parameter

51. Derivation of CRR-KD curves from CPT-SPT
Recommended CRR curves for CPT and SPT
NCEER Workshops – Youd & Idriss (2001)
Evaluate DR corresponding to CRR-CPT and CRR-SPT curves by current DR - qc and DR - NSPT correlations
DR - qc : Baldi et al. (1986), Jamiolkowski et al. (1985)
DR - NSPT : Gibbs & Holtz (1957)
"Equivalent" CRR-KD curves
Evaluate KD corresponding to calculated DR using the KD - DR correlation by Reyna & Chameau (1991)

52. "Equivalent" CRR-KD curves from CPT qc1N = (pa /'vo ) n (qc /pa )
CRR- qc1N curve
DR from qc1N
DR - qc correlations
Baldi et al. (1986)
Jamiolkowski et al. (1985)
CSR or CRR
KD from DR
DR - KD correlation
Reyna & Chameau (1991)
qc1N = (pa /'vo ) n (qc /pa )
CRR-KD curve

53. "Equivalent" CRR-KD curves from SPT
CRR- (N1) 60 curve
CSR or CRR
DR from (N1) 60
DR - NSPT correlations
Gibbs & Holtz (1957)
KD from DR
DR - KD correlation
Reyna & Chameau (1991)
(N1) 60 = Nm CN CE CB CR CS
CRR-KD curve

54. New tentative CRR-KD curve Monaco et al. (2005) – ISSMGE Osaka
0.5
0.4
0.3
0.2
0.1
M = 7.5
Reyna & Chameau 1991
CSR or
CRR
Range of curves derived from CPT
LIQUEFACTION
Marchetti 1982
New tentative
CRR-KD curve
Monaco et al. 2005
Range of curves derived from SPT
Robertson & Campanella 1986
NO LIQUEFACTION KD
Monaco et al. (2005) – ISSMGE Osaka

55. CRR-KD curve vs Loma Prieta 1989 earthquake liquefaction datapoints
CSR or
CRR
CRR-KD curve
Monaco et al. (2005)
LIQUEFACTION
LIQUEFACTION SITES
Port of Richmond POR2
Port of Oakland POO7-2
Port of Oakland POO7-3
Alameda Bay - South Loop Rd.
NON CLASSIFIED SITES
Port of Richmond - Hall Ave.
LOMA PRIETA 1989
EARTHQUAKE
DMT & earthquake data after
Mitchell et al. (1994)
Report No. UCB/EERC-94/0
see also Coutinho & Mitchell (1992)
NO LIQUEFACTION KD

56. Minimum "no liquefaction" KD values
In many everyday problems useful guidelines to identify if soil clearly liquefiable or non liquefiable
Tentative identification of MINIMUM values of KD for which a clean sand (natural or sandfill) is safe against liquefaction for M = 7.5 earthquakes (TC ):
– Non seismic areas, i.e. very low seismic:
KD > 1.7
– Low seismicity areas (amax /g = 0.15):
KD > 4.2
– Medium seismicity areas (amax /g = 0.25):
KD > 5.0
– High seismicity areas (amax /g = 0.35):
KD > 5.5
MARGINAL values to be factorized by adequate Fs

57. Final remarks
CRR from DMT-KD alternative / integration to CRR from current methods (CPT, SPT, VS …)
Redundant evaluation of CRR by more than one method generally recommended
Parallel independent evaluations of CRR from KD and VS by seismic dilatometer SDMT
KD sensitive to DR and to factors that greatly increase CRR – stress/strain history, aging, cementation, structure
Research suggests some link between KD and State Parameter – probably closest proxy of liquefiability
Considerable additional verification needed, supported by more real-life liquefaction case histories