WP 3 : DESIGN TOOLS

1

• WP 3 DESIGN TOOLS
• PART 1 USE OF FINITE ELEMENT METHOD
• IN GEOTECHNICAL DESIGN
• Overview of the basic document

2

• WP 3 DESIGN TOOLS
• PART 1 USE OF FINITE ELEMENT METHOD
• IN GEOTECHNICAL DESIGN
• Overview of the basic document
• Choice of soil model, parameters and initial
  stresses

3

• WP 3 DESIGN TOOLS
• PART 1 USE OF FINITE ELEMENT METHOD
• IN GEOTECHNICAL DESIGN
• Overview of the basic document
• Choice of soil model, parameters and initial
  stresses
• Proposal of future actions

4
OVERVIEW OF THE BASIC
DOCUMENT New version will be soon
available on the website
5

• Different types of numerical methods
• Value of numerical methods
• Fundamental principles of FEM
• Approach for the user
• FEM for different types of construction
• Inventory of ressources
• List of references

6

• Different types of numerical methods
• Value of numerical methods
• Fundamental principles of FEM
• Approach for the user
• FEM for different types of construction
• Inventory of ressources
• List of references

7
Value of numerical methods

• When analytical methods are insufficient or
  impossible
• Complex geometry
• Soil-structure interaction
• Settlements

8
Value of numerical methods

• When analytical methods are insufficient or
  impossible
• Complex geometry
• Soil-structure interaction
• Settlements
• To
• Calculate stresses and deformations and compare
  them to allowable values
• Parameter studies

9
Value of numerical methods

• Tool for Observational Method
• To identify representative and critical locations
  for installation of measuring apparatus
• Measurements during early stages ? calibration of
  the model ? better prediction of final situation
  ? possibility of early intervention

10
Approach for the user sources of uncertainties

• Numerical aspects
• convergence,
• discretisation,

11
Approach for the user Sources of uncertainties

• Numerical aspects
• convergence,
• discretisation,

• Models
• geometry,
• soil,
• structural elements,
• interfaces,
• construction stages

12
Approach for the user Sources of uncertainties

• Numerical aspects
• convergence,
• discretisation,
• Type of analysis
• drained/undrained/consolidation,
• initial stresses,
• water condition

• Models
• geometry,
• soil,
• structural elements,
• interfaces,
• construction stages

13
Approach for the user Sources of uncertainties

• Numerical aspects
• convergence,
• discretisation,
• Type of analysis
• drained/undrained/consolidation,
• initial stresses,
• water condition

• Models
• geometry,
• soil,
• structural elements,
• interfaces,
• construction stages
• Model parameters

14
(No Transcript)
15
Approach for the user Sources of uncertainties

• Numerical aspects
• convergence,
• discretisation,
• Type of analysis
• drained/undrained/consolidation,
• initial stresses,
• water condition

• Models
• geometry,
• soil,
• structural elements,
• interfaces,
• construction stages
• Model parameters

16
CHOICE OF SOIL MODEL, PARAMETERSAND INITIAL
STRESSES
17
Choice of soil model

• Because of none of the currently availabe soil
  constitutive models can reproduce all of the
  aspects of real soil behaviour, one have to make
  a choice, taking into account
• the nature of the subsoil,

18
Choice of soil model

• Because of none of the currently availabe soil
  constitutive models can reproduce all of the
  aspects of real soil behaviour, one have to make
  a choice, taking into account
• the nature of the subsoil,
• the soil features that govern te behaviour of a
  particular geotechnical problem stiffness,
  strength,

19
Choice of soil model

• Because of none of the currently availabe soil
  constitutive models can reproduce all of the
  aspects of real soil behaviour, one have to make
  a choice, taking into account
• the nature of the subsoil,
• the soil features that govern te behaviour of a
  particular geotechnical problem stiffness,
  strength,
• the availability of soil data

20
Choice of soil model

• Elastic material models
• Elasto-plastic material models
• Different programming codes of essentially the
  same material model may lead to different answers
  !!!
• Strain hardening and strain softening material
  models
• Stress history
• Real soil behaviour strongly depends on previous
  and current stress paths, stress history. This
  may be described by introducing several moving
  yield surfaces or "history surfaces"

21
Choice of soil model
22
Choice of soil model

• Example Tests on shallow foundation at Labenne
  (sand)
• Mestat, Berthelon
• In general better results with the Nova model
  (elasto-plastic with hardening) than with the MC
  model

23
Choice of soil model

• LSD 2000 International Workshop on Limit State
  Design in Geotechnical Engineering
• Melbourne, Australia, 18 November 2000
• Some Considerations on the Use of Finite
  Element Methods in Ultimate Limit State Design
• C. Bauduin
• Besix, Brussels Brussels University
• M. De Vos
• Belgian Building Research Institute, Brussels
• B. Simpson
• Arup Geotechnics, London

24
Choice of soil model

• Examples, using MC and hardening model
• seems to be no significant effect on the ULS of
  the soil
• more significant role on the ULS in structural
  elements, especially for stiff, brittle
  structures ? advanced model may be needed

25
Choice of soil model

• Empfehlungen des Arbeitskreises Numerik in der
  Geotechnik
• Although a linear elastic model is a very
  simplified way to represent soil behaviour, it
  gives often a good estimation (bearing capacity,
  forces, soil-structure interaction,)

26
Choice of soil model

• David M Potts and Lidjia Zdravkovic, 2001
• Soil dilation can have a dominant effect on pile
  behaviour and consequently care must be exercised
  when selecting an appropriate constitutive model
  and its parameters

27
Choice of soil model

• Guidelines are sometimes confusing
• more detailed analysis is needed

28
Input parameters

• Measured values of soil properties can be
  greatly affected by factors such as sampling,
  handling and preparation, precision of testing
  technique,
• Confining pressure the stress-strain behaviour
  of soil is nonlinear. For all cases except
  saturated soil under undrained conditions, the
  stress strain behaviour of soil depends on
  confining pressure.
• Preliminary design values from litterature,
  experience
• Design values from tests if necessary,
  perform a calculation with upper and lower limit
  of parameter values

29
Input parameters

• Tests for parameter determination
• Laboratory tests
• Field tests
• Correlations with index property values
• Calibration studies

30
Input parameters

• Calibration studies
• In many cases, designers have experience with
  local soils and are skilled at calculating 1-D
  consolidation settlements using conventional
  procedures. It is good practice in such cases to
  develop a 1-D column of finite elements that
  models the soil profile at the site of interest.
  The 1-D column can be loaded and the resulting
  settlements compared to those calculated using
  conventional procedures. The material property
  values for the finite element analyses can be
  adjusted until a match is obtained. Similarly, if
  an independent estimate of the lateral load
  response, i.e., the Poisson effect, can be made,
  the material property values can be adjusted
  until the 1-D column results match the
  independent estimate. Ideally, one set of
  material property values would be found that
  provides a match to both the compressibility and
  the lateral load response over the range of
  applied loads in the problem to be analysed.

31
Input parameters

• Illustration with case studies
• Limelette
• Sint Katelijne Waver

32
Limelette site
Input parameters
33
CPTs (qc) Limelettedynamic field static field
Input parameters
34
Sint Katelijne Waver site
Input parameters
35
CPTs (qc) Sint Katelijne Waver
Input parameters
36
Strength parameter F ( Limelette )
Input parameters

• Application of correlations established for
  sands from in situ tests to the sandy layer in
  Limelette (8,2m 16m)
• From CPTs
• Robertson Campanella, 1983
• Meyerhoff, 1956
• Olsen Farr, 1986
• From SPTs
• Stroud, 1989 (OCR 3)
• Peck et al, 1974
• Terzaghi Peck, 1967
• From DMTs
• Durgonoglu Mitchell (OCR 3)

37
Static field
Input parameters
38
Dynamic field
Input parameters
39
Strength parameter F ( Limelette )
Input parameters

• Application of correlations established for
  silts from in situ tests to the silty layer in
  Limelette (2,2m 6,2m)
• From SPTs
• Terzaghi Peck, 1967
• From DMTs
• Durgunoglu Mitchell

40
Static field
Input parameters
41
Dynamic field
Input parameters
42
Summary ? Sand Limelette
Input parameters

• Static field
• 8,2-10,2m
• From CPTs Fpeak 41 47
• From SPTs Fpeak 35 38
• From DMTs Fpeak 40
• 10,2-16m
• From CPTs Fpeak 38 44
• From SPTs Fpeak 35 38
• From DMTs Fpeak 40
• Triaxial tests Fpeak 35

• Dynamic field
• 8,2-10,2m
• From CPTs Fpeak 41 46
• From SPTs Fpeak 35 38
• From DMTs Fpeak 40
• 10,2-12,2m
• From CPTs Fpeak 40 44
• From SPTs Fpeak 35 38
• From DMTs Fpeak 40
• 12,2-16m
• From CPTs Fpeak 38 42,5
• From SPTs Fpeak 34 37
• From DMTs Fpeak 40
• Triaxial tests Fpeak 35

43
Summary ? Silt Limelette
Input parameters

• Static field
• From SPTs Fpeak 31 35
• From DMTs Fpeak 35
• Triaxial tests Fpeak 35

• Dynamic field
• From SPTs Fpeak 31 35
• From DMTs Fpeak 35
• Triaxial tests Fpeak 35

44
Conclusions determination of F
(Sand Silt Limelette)
Input parameters

• CPTs correlations are established mainly for
  sandy soils. When applicated to the sandy layer
  of the Limelette site, the differences between
  the different correlations arein the range of 5.
• SPTs correlations are established for silty and
  sandy soils. When applicated to the sandy layer
  of the Limelette site, the differences are in the
  range of 3.
• DMTs correlations are established for silty and
  sandy soils.
• Comparison between the Fpeak value deduced from
  CPTs, SPTs, DMTs and triaxial tests
• Fpeak,triaxial Fpeak, DMT lt Fpeak,SPT lt
  Fpeak, CPT

45
Strength parameter cu ( Sint Katelijne Waver )
Input parameters

• Application of correlations established for
  clays from in situ tests to the stiff
  overconsolidated tertiary clay of Sint Katelijne
  Waver
• From CPTs
• Carpentier, 1970
• Marsland Quaterma, 1982
• From SPTs
• Stroud, 1989
• From DMTs
• Marchetti, 1980

46
Input parameters
47
Summary cuTertiary Overconsolidated Clay Sint
Katelijne Waver
Input parameters

• From CPT (Carpentier) cu (kPa) 8,22 z (m)
  65
• From CPT (Marsland and Quaterma) cu (kPa)
  5,01 z (m) 46
• From SPT (Stroud) cu (kPa) 5,18 z (m) 47
• From DMT (Marchetti) cu (kPa) 12,26 z (m)
  50
• UU triaxial tests cu (kPa) 11,3 z (m) 34

48
Deformation parameter Eoed ( Limelette )
Input parameters

• Application of correlations from in situ tests
  to the site of Limelette
• From CPTs
• Sanglerat, 1972
• From PMTs
• Nuyens
• From DMTs
• Totani, Marchetti, Monaco Calabrese

49
Static field
Input parameters
50
Dynamic field
Input parameters
51
Deformation parameter Eoed ( Sint Katelijne
Waver )
Input parameters

• Application of correlations established for
  clays from in situ tests to the stiff
  overconsolidated tertiary clay of Sint Katelijne
  Waver
• From CPTs
• Sanglerat, 1972
• From PMTs
• Nuyens

52
Input parameters
53
Input parameters

• Example Tests on shallow foundation at Labenne
  (sand)
• Mestat, Berthelon
• Vertical displacements are largely underestimated
  (soil model MC).
• The causes of this may be
• Fluctuation of the water level, capillary
  cohesion, no-representativity of the laboratory
  tests,  simplicity  of the MC model, local
  heterogeneities
• Mostly wrong estimation of the Young modulus.
  From laboratory test initial modulus, more
  realistic lower modulus, for example from in
  situ pressiometric tests (contrary to the
  simulation of other constructions where the
  values of laboratory tests gave acceptable
  results).

54
Input parameters

• importance of calibration studies
• be careful with correlations
• more information needed more specific per
  region/country ?
• deformation parameters from in situ tests
  better from PMT ?
• taking into account the soil model used

55
Initial stresses

• Empfehlungen des Arbeitskreises Numerik in der
  Geotechnik
• initial stress state often an important
  factor
• The initial stress state depends on
• soil density
• soil shear strength characteristics
• load history (geology, consolidation)
• la yers in rock
• sliding surfaces
• water flow

56
Initial stresses

• Empfehlungen des Arbeitskreises Numerik in der
  Geotechnik
• initial stress state often an important
  factor
• The initial stress state depends on
• soil density
• soil shear strength characteristics
• load history (geology, consolidation)
• la yers in rock
• sliding surfaces
• water flow
• ? difficult to predict with precision

57
Initial stresses

• perform different calculations with different
  initial stresses
• include the history in the first calculation step
• impose displacements of nodes
• first, perform a calculation with a large soil
  volume,
• then, perform a calculation with a smaller soil
  volume for which the bounderies are taken from
  the first calculation

58
Initial stresses

• LSD 2000 International Workshop on Limit State
  Design in Geotechnical Engineering
• Melbourne, Australia, 18 November 2000
• Some Considerations on the Use of Finite
  Element Methods in Ultimate Limit State Design
• C. Bauduin
• Besix, Brussels Brussels University
• M. De Vos
• Belgian Building Research Institute, Brussels
• B. Simpson
• Arup Geotechnics, London

59
Initial stresses

Design Characteristic value
value Soil strength parameters Init.
stresses M d1, Ad1 Stage
1 Md2, Ad2 Stage 2
Stage 3 Final situation Time
(stage)
60
Initial stresses

• NC soils MC or hardening model
• no significant effect of initial stress field
  (characteristic or design) on ultimate state of
  the soil
• may be very important, when looking to ULS in
  structural elements

61
PROPOSAL OF FUTURE ACTIONS
62
Future actions

• add other available information (Cost C7,
  benchmarks,), with special attention to
• soil models
• (initial stresses)
• parameter determination strength / deformation
• others ?
• summary of benchmarks
• (new benchmarks)

63
Future actions

• application of safety factors

64
(No Transcript)