RWSGrontmijWitteveen Bos

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MoU on Soft Soil Engineering1996 - 2001
Regional Teaching Program 2001 General Plaxis
theory and exercises Republic of Indonesia
Kingdom of the Netherlands RT-06 July 9th -
2001
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General Plaxis theory and exercisesContents

• On the use of Plaxis
• Exercise 1
• Exercise 2

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On the Use of Plaxis

• Create geometry model
• a composition of
• points
• lines
• clusters
• division of subsoil
• layers
• structural objects
• construction stages
• loading
• large enough, so no boundary disturbances

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On the Use of Plaxis

• Using
• points
• startend of lines
• used for positioning of anchors, fixities
• lines
• physical boundaries of geometry
• model boundaries
• discontinuities (structural elements, soil
  layers)
• clusters
• areas enclosed by lines
• homogenous soil properties

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On the Use of Plaxis

• After defining geometry
• Create Finite Elements model automatically
• triangular elements, 6 or 15 noded

• Elements
• 6 or 15 noded
• 3 or 12 stress points

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On the Use of Plaxis

• How to use Plaxis?
• Plaxis consists of following modules
• Plaxis Input
• Plaxis Calculations
• Plaxis Output
• Plaxis Curves

demo
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Exercise 1 Getting Familiar
Goal

• Get familiar using the Plaxis code
• Basic concept I
• input geometry structural elements
• applying boundary conditions
• applying loading and/or prescribed
  displacements
• entering material properties
• mesh generation

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Exercise 1 Getting Familiar II

• Basic concept II
• initial flow and consolidation boundary
  conditions
• generation initial pore water pressures
• initial stresses
• Basic concept III
• calculation

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Exercise 1 Elastic analysis of drained footing
on clay
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Material properties of the clay and concrete
footing
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Hints

• Use 6-noded elements
• Choose plane strain model (strip footing)
• Freatic line at top surface
• Use drained material behaviour OPTION 2
  Undrained
• Choose Load A (vertical) and Load B 1 kN
• (Total load, ?MloadA100), ?MloadB100 kN)

Question Calculate the deformations.

• K0 condition, K00.7
• Stage 1, Construction of footing (staged
  construction)
• Stage 2, apply vertical load
• Stage 3, apply horizontal load

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Exercise 2 Elasto-plastic analysis of drained
footing.

• Use same geometry as exercise 1
• Refine Mesh Global (New)
• Use Mohr Coulomb model, see table 2 (New)
• Use 15- noded elements
• Define load displacement points (New)
• Only apply vertical force, ?MloadA 500 kN/m

Question Determine the failure load (Bearing
capacity)
Answer
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Table2 Material properties of the clay and
concrete footing
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Stress points and nodes
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Applying load due to body forces
K0-procedure
?MWeight
Module
Geo
Calculations
Step 0
--
staged constructions
Step 1
staged constructions
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Exercise 3, calculation of settlements

• Determine the final primary settlements using
• Fully drained
• Hand calculation (Terzaghi formulation)
• Msettle 1-dimensional program
• FEM program Plaxis using Soft Soil Model

For material properties see Table 3.1 on next
slide
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Exercise 3, calculation of settlements
Terzaghi
Table 3.1 material properties
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Exercise 4, Road Embankment

• Building of a road embankment on soft soil, thus
• undrained behavior of soft soil
• generation of excess pore pressures

• Two new options
• consolidation
• safety analysis by means of c-tan(?) reduction
• Divide embankment into two horizontal layers

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Exercise 4, road embankment
Material properties
Freactic line coincides with original ground
level
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Exercise 4, road embankment

• Boundary conditions
• use symmetric geometry (half of embankment)
• standard fixities for horizontal and vertical
  displacement

NEW

• Closed flow boundary at centerline
• flow only out of vertical boundaries at surface
  and bottom
• no flow at left and right boundary

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Exercise 4, road embankment

• Calulation stages
• determine initial condition, using K0 option
• activate first part of embankment, using Staged
  Construction
• consolidation for 200 days (NEW)
• activate second part of embankment, using Staged
  Construction
• consolidation, minimum pore pressure is 1 kN/m2

Displacement increments after first stage
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Exercise 4, road embankment

• Safety analysis (NEW)
• determine safety factor after first construction
  stage
• determine safety factor after second
  construction stage
• determine long term safety factor

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Exercise 5, Bishop Stability analysis (Mstab)

• Determine the stability factor using Bishop slip
  analysis
• Use the same strength parameter c and ? as in
  exercise 3
• calculate SF for fully drained condition (final
  stability factor)