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

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. Introduction. Reasonable mesh type in association with CPU time

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

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  1. 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

  2. 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) 14th Crisp user meeting at UCL

  3. Laboratory test using ideal material (Aluminium rods) 2D model pile-load test P-S curve 14th Crisp user meeting at UCL

  4. Plane Strain Mesh Mesh A • Total 639 nodes • Total 1160 elements: 1132 LSTs + 28 LSQs 14th Crisp user meeting at UCL

  5. Plane Strain Mesh Mesh B • Total 195 nodes • Total 176 elements: 4 LSTs + 172 LSQs 14th Crisp user meeting at UCL

  6. 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 14th Crisp user meeting at UCL

  7. Analysis conditions: DCM 1. Simulation of pile loading Pile head settlements from the pile 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 4. Number of increments 320 increments 14th Crisp user meeting at UCL

  8. Increment Block Parameters 14th Crisp user meeting at UCL

  9. Increment size effect (based on  = 20°) Dilation angle effect (based on total 320 increments) Displacement norm convergencecheck for the Mesh B 14th Crisp user meeting at UCL

  10. Comparison of CPU times More than 1hr Less than 12min 14th Crisp user meeting at UCL

  11. ICFEP (by Potts et al, 1999) The MNR results are insensitive to increment size e.g. Pile problem: SAGE CRISP The MNR results are dependent on increment size The MNR solution was not fully implemented in connection with relationship between load and 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 Comparison of Modified Newton-Raphson methods 14th Crisp user meeting at UCL

  12. 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. 14th Crisp user meeting at UCL

  13. Results of plastic stage (20 – 30Kg) • Vector movements • Horizontal displacement contours • Vertical displacement contours • Volumetric strain contours • Max. shear strain contours • Major principal strain directions • Zero extension line directions Note that these displacements are associated with strain fields in soil mechanics problems 14th Crisp user meeting at UCL

  14. Experimental result from the photo image processing (Scale:15) SAGE CRISP (M.F.=10) based on the mesh B ( = 20°) 1. Vector movements 14th Crisp user meeting at UCL

  15. 2. Horizontal displacements Experimental result SAGE CRISP 14th Crisp user meeting at UCL

  16. 3. Vertical displacements Experimental result SAGE CRISP 14th Crisp user meeting at UCL

  17. 4. Dilatant volumetric strains Experimental result SAGE CRISP 14th Crisp user meeting at UCL

  18. 5. Max. shear strains Experimental result SAGE CRISP 14th Crisp user meeting at UCL

  19. 6. Major principal strain directions Experimental result SAGE CRISP 14th Crisp user meeting at UCL

  20. 7. Zero extension line directions(/or Slip line directions) Experimental result SAGE CRISP 14th Crisp user meeting at UCL

  21. 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

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