# Numerical analysis of pile-load test in granular material using by rma97348

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```									Numerical analysis of a piled foundation in
granular material using slip element

Yongjoo Lee
Soil Mechanics Group
Department of Civil and Environmental Engineering
University College London
Gower Street, London WC1E 6BT

14th Crisp user meeting at UCL         1
Introduction
• Reasonable mesh type in association with CPU
time
• Number of increments for displacement norm
convergence in connection with MNR
(Modified Newton-Raphson)
• Values of dilation angle () for displacement
norm convergence under New Mohr-Coulomb
soil model (Non-associated flow rule applied)

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Laboratory test using ideal material
(Aluminium rods)
2D model pile-load test                            P-S curve

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Plane Strain Mesh
Mesh A

   Total 639 nodes

   Total 1160 elements:
1132 LSTs + 28 LSQs

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Plane Strain Mesh
Mesh B

   Total 195 nodes

   Total 176 elements:
4 LSTs + 172 LSQs

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Parameters (drained condition)

   Granular material: Hypothetical
elastoplastic material based on New
Mohr-Coulomb model – Linear
elastic perfectly plastic model
C = 0.1Kpa,  = 30°,  = 20°,  =
0.35, E0 = 1600Kpa, mE = 40000Kpa,
bulk = 24KN/m3 , Y0 = 0.72m
   Slip model:
C = 0.005Kpa,  = 5°, Kn =
16000Kpa, Ks=8000Kpa, Ksres =
0.8Kpa, t = 0.1m
   Concrete pile: Isotropic elastic
model
E = 1.55e7Kpa,  = 0.2, bulk =
23KN/m3

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Analysis conditions:
DCM
Pile head settlements from the pile
applied y
load test applied to the centre node
of the pile head (i.e. DCM)

2. Iterative solution scheme
MNR (Modified Newton-Raphson)
Tolerance: 0.05, Max. iteration: 40

3. In-situ stress condition
K0 = 0.5
Pile element

4. Number of increments                                        Slip element

Soil element
320 increments

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Increment Block Parameters
Increment    Increment      Pile head settlement     Time-               Number of Increments
Block No.    Block List             (mm)           Step (sec)
Case 1     Case 2   Case 3      Case 4

1         Install pile            0                 1          5          5         5          5

2        y1 = 0.08mm       0+0.08=0.08             1          5          10       20          5

3        y2 = 0.6mm        0.08+0.6=0.68           1          5          10       20         20

4        y3 = 0.32mm       0.68+0.32=1             1          5          10       20         40

5        y4 = 1.34mm       1+1.34=2.34             1          5          10       20         50

6        y5 = 1.95mm      2.34+1.95=4.29           1          5          10       20         50

7        y6 = 3.71mm       4.29+3.71=8             1          5          10       20         50

8        y7 = 3.83mm       8+3.83=11.83            1          5          10       20         50

9        y8 = 8.56mm     11.83+8.56=20.39          1          5          10       20         50

Total              20.39               9         45          85       165        320

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Displacement norm convergence
check for the Mesh B

   Increment size effect                          Dilation angle effect
(based on  = 20°)                               (based on total 320 increments)

Number of            convergence                 Dilation angle          convergence
increments                                         (degrees)
45                   No                                 0                  No
5                  No
85                   No
10                     No
165                   Yes
15                     No
320                   Yes                            20                    Yes

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Comparison of CPU times

4000
More than 1hr
3500

3000
CPU time (sec)

2500

2000

1500

1000
Less than 12min
500

0
Mesh A                               Mesh B
Types of mesh

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Comparison of
Modified Newton-Raphson methods
   ICFEP (by Potts et al, 1999)                   SAGE CRISP
The MNR results are insensitive to              The MNR results are dependent on
increment size                                  increment size
e.g. Pile problem:
The MNR solution was not fully
implemented in connection with
displacement norms, being based
only on the displacement norm
convergence checking system at the
moment

   There is no detailed information of the
MNR iterative solution in the Crisp
technical manual

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Conclusions
   CPU time can be improved through the reasonable mesh type
using the Linear strain quadrilateral elements (i.e. LSQs).

   In numerical analysis using the slip element, the MNR iterative
solution result is very sensitive to the number of increments (or
increment size) in contrast to the comment by Potts et al. (1999).

   In the New Mohr-Coulomb soil model (i.e. linear elastic perfectly
plastic model), the value of dilation angle () is a key factor in
order to satisfy the displacement norm convergence.

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Results of plastic stage (20 – 30Kg)
1.   Vector movements
2.   Horizontal displacement contours
3.   Vertical displacement contours
4.   Volumetric strain contours
5.   Max. shear strain contours
6.   Major principal strain directions
7.   Zero extension line directions

Note that these displacements are associated with
strain fields in soil mechanics problems

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1. Vector movements
Experimental result from the                SAGE CRISP (M.F.=10) based
photo image processing (Scale:15)           on the mesh B ( = 20°)

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2. Horizontal displacements
Experimental result                                                    SAGE CRISP
Horizontal displacement contour

700.00

6.00
5.50
600.00
5.00
4.50
4.00
3.50
3.00
2.50
500.00                                                                 2.00
1.50
1.00
0.50
0.00
-0.50
-1.00
400.00                                                                 -1.50
-2.00
-2.50
-3.00
-3.50
-4.00
-4.50
300.00

300.00   400.00      500.00        600.00       700.00   800.00

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3. Vertical displacements
Experimental result                                                    SAGE CRISP
Vertical displacement contour

700.00

600.00                                                                 6.50
6.00
5.50
5.00
4.50
4.00
3.50
500.00                                                                 3.00
2.50
2.00
1.50
1.00
0.50
0.00
400.00                                                                 -0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
300.00

300.00    400.00      500.00       600.00       700.00   800.00

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4. Dilatant volumetric strains
Experimental result                                                    SAGE CRISP
Volumetric strain contour

700.00

0.10

0.00
600.00
-0.10

-0.20

-0.30
500.00
-0.40

-0.50

-0.60

400.00                                                            -0.70

-0.80

300.00

300.00   400.00        500.00         600.00    700.00      800.00

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5. Max. shear strains
Experimental result                                                    SAGE CRISP
Shear strain contour

700.00

0.80

0.70
600.00
0.60

0.50

0.40

500.00                                                            0.30

0.20

0.10

0.00
400.00
-0.10

300.00

300.00   400.00        500.00         600.00    700.00    800.00

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6. Major principal strain directions
Experimental result                                    SAGE CRISP

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7. Zero extension line directions
(/or Slip line directions)
Experimental result                               SAGE CRISP

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Numerical analysis of a piled foundation in
granular material using the slip model

Yongjoo Lee
Soil Mechanics Group
Department of Civil and Environmental Engineering
University College London
Gower Street, London WC1E 6BT

14th Crisp user meeting at UCL         21

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