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MoU on Soft Soil Engineering1996 - 2001
Regional Teaching Program 2001 Settlements theory
and exercises Republic of Indonesia Kingdom of
the Netherlands RT-08 July 9th - 2001
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Settlements theory and exercisesContents

• Settlements phenomena
• Basic Settlement formulation
• Fokkens method
• Consolidation
• Calculation accuracy

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Settlements phenomena

• Settlements due to fill placement
• Settlement due to widening of embankment
• Land subsidence
• Fluctuation of surface and groundwater level
• Vibration

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Fill placement/Widening

• increase of load
• increase total stresssesw
• fast loadinggtundrained behaviour
• increase pore pressure
• low shear resistance
• gtfailure

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Land subsidence

• Increase of stress due to weight of soil
• rearrangement of grains
• decrease of voids
• increase load on subsoil
• leads to settlements in subsidencesub-soil

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Basic settlement formula

• Anglo Saxon method (BS and NEN)
• Den Haan-Fokkens methods
• Consolidation
• End of consolidation
• consolidation coefficient with more layers

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Anglo Saxon method
Relation compression and logarithm of load
(Terzaghi)
C
the primary Compression Index
-
c
h thickness
m
d
h settlement
m
e0 initial void ratio
-
2
s
initial effective stress
kN/m

0
D
s
2

Increase of effective
stress kN/m

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Anglo Saxon method

• Using compression Ratio CR

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Unloading-Reloading
l 2.3Cc k 2.3 Cs
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Secondary compression
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Total Settlements
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Determine parameters
Oedometer
- consolidation ring - porous plates -
consolidation cell - micrometer dial gauge -
loading device
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Oedometer test
According NEN 5118

• initial load 3.69 kPa
• doubled every 24 h.
• Max load 236 kPa (6 load steps)
• Creep test

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Results oedometer test
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Fokkens/Den Haan (1)

• Determine compression of peats
• relation between Aeging, water content w, organic
  material N content and se
• Normally consolidated peat
• use of
• concept of aeging
• log. Compression law

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Fokkens/Den Haan (2)
With w water content after load N
ignition loss (5 h. at 550º) - s effective
stress kN/m2 Den Haan
he ultimate compression wi initial water
content
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Consolidation (1)

• Terzaghi consolidation theory
• homogenious soil
• fully saturated
• granular material and water incompressable
• lin. Correlation compression and stress
• cv constant
• small compression compared to thickness layer

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Consolidation (2)
One dimensional
With
u excess pore water pressure kPa t time
s cv vertical coefficient of
consolidation m2/s z coordinate in z
direction depth m k vertical permeability
coefficient m/s mv vertical coefficient of
volume compressibility m2/kN (w unit weight
of water kN /m2
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Consolidation (3)
Analytical solution
One-way drainage
Boundary condition Top u0
Two-way drainage
Boundary condition Top and bottom u0
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Consolidation (4)

• Ratio of compression at time t and tfinal,
• gt defined as Degree of consolidation U

With T time factor
T time factor, - t time duration s a
drainage constant, a 1.0 for one way
drainage, a 0.5 for two way drainage h
layer thickness m
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Consolidation (5)
Practical end of consolidation U0.994
(T2.0) Consolidation time te
For peat Dte
years (cv10)
years (cv2.5)
For Clay Dte
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Consolidation (6)
More layers adjusting cv to cv,eq
cv,eq equivalent coefficient of consolidation
for total height m2/s hi thickness of
layer i m cv,I coefficient of
consolidation of layer i m2/s

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Calculation accuracy

• Depends on
• Physical aspects
• heterogenity of the soil
• heterogenity of sampling
• lab and in-situ testing
• determination of parameters
• Choice of formulations
• Modeling aspects
• geometry and boundary conditions
• loading and stress distribution

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Exercises

• Settlement analysis using
• Msettle
• Plaxis
• hand calculations
• Exercise I
• Footing problem (analytical and using FEM)
• Exercise II
• Road embankment

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Exercise I, Drained Footing
Elastic
Objective Calculate the deformation
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Exercise I, Drained Footing

• Geometry input
• boundary conditions
• material properties (Elastic)
• mesh generation
• initial condition
• calculations
• construction of footing
• apply vertical load
• apply horizontal load
• Inspect output

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Exercise I, Drained Footing
Material properties
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Exercise I, Drained Footing
Output
Extreme displacement 28 mm
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Exercise II, Drained Footing Mohr Coulomb

• 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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Exercise II, Drained Footing MC model
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Exercise II

• Analytical solution by Vesic

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Exercise III, Undrained footing
Same exercise as II, but now using undrained soil
behaviour Note In Plaxis, change in material
properties drained to undrained
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Exercise IV Road embankment

• Objective Calculate final settlements
• Conditions
• Fully drained
• Mohr Coulomb model

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Exercise IV, road embankment
Material properties for settlement analysis
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Exercise IV, road embankment

• Geometry input
• boundary conditions
• material properties (Drained)
• mesh generation
• initial condition
• calculations
• initial stress sub-soil
• build the embankment (drained)
• Inspect output
• determine finale settlements

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End of Settlements
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