Zeynep ÇEKİNMEZ MSc Civil Engineer

1. Middle East Technical University Civil Engineering Department GENERAL INFORMATION ABOUT PLAXIS 2D and an EXAMPLE OF BRACED EXCAVATION in PLAXIS 2D Zeynep ÇEKİNMEZ MSc Civil Engineer

2. OUTLINE • General Information about Plaxis • General Information about Plaxis 2D • Types of Modelling • Examples of Graphical Input of Geometry Models • Elements used in Geometry Models • Required Input Soil Parameters • General Procedure of Analysis • Flow Chart • Step by Step Modelling an Example: “Assignment #6: Braced Excavation for Sewage Pipe System” • Interpretation of results of the example • Comparision of hand calculation and PLAXIS results • Analysis in Plaxis Flow • Flow Input • Step by Step Modelling

3. General Information about Plaxis • Software is from Delft/Netherlands • Most widely-used software in geotechnical aspects: • Researchers (MS and Phd students) • Project Analysis • Design Applications • Synchronizing the real behavior of in-situ soil and the calculated one. • User friendly, Finite Element Program (FE programe) • Stresses developed at stress points • Strains developed at nodes By using STIFFNESS MATRIX [E]

4. General Information about Plaxis • PLAXIS is a software analysing deformation, stresses and stability validation that occur in constructions in the field of geotechnical engineering by step by step constructionStaged Construction. • PLAXIS software has various versions each analysis different type of structures/problems: • PLAXIS 2D Foundation • PLAXIS 2D Dynamics • PLAXIS 2D Tunnel • PLAXIS 2D Flow • PLAXIS 3D Foundation • PLAXIS 3D Tunnel

5. General Information about Plaxis 2D

6. Types of Modelling Plaxis 2D provides two different type of modelling: 1) Plane Strain • Used for geometries with a (more or less) uniform cross section and corresponding stress state and loading scheme over a certain length perpendicular to the cross-section (z-Direction) • Displacements and strains in z-direction are assumed to be zero. However normal stresses in z-direction are fully taken into account y Inputs and outputs are in unit/m x

7. Types of Modelling 2) Axisymmetric model • Used for circular structures with a (more or less) uniform radial cross section and loading scheme around to be identical in any radial direction. • Note that for axisymmetric problems the x-coordinate represents the radius and the y-coordinate corresponds to the axial line of symmetry. Negative x-coordinates cannot be used. y x 1rad Inputs and outputs are in unit/2π

8. Graphical input of geometry models Node-to-Node Anchors-Struts Surcharge Plate Elements Interfaces Boundary Condition: ux=0, uy is free Boundary Condition: ux=0, uy=0

9. Graphical input of geometry models Node-to-Node Anchors-Tie Backs Geogrid-Anchor Grout

10. Elements Used in Geometry Models Used Elements • Plates (foundations, walls, plates, piles etc.  structural members) • Node-to-Node Anchors (struts, anchor tie-backs) • Fixed-Anchors (for symmetric design instead of node-to-node anchors) • Geogrids (Anchor grout, geosythetics) • Interface (soil-structure interaction, flow conditions) • Tunnel • Hinge/Rotation (Connections of structural members) • Prescribed Displacement • Distributed/Point Load • Well • Drain

11. Soil Models Soil Models (stress-strain relation depending on constant/varying stiffness): • Mohr-Coulomb (general) • Hardening Soil Model (in unloading-loading sequences) • HS Small Model (small strains in hardening soils) • Soft Soil Model (for clays, primary consolidation) • Soft Soil Creep Model (for creep soils in soft clays, secondary consolidation) • Joint Rock Model (for rock and its special characteristics)

12. Required Soil Input Parameters

13. Required Soil Input Parameters

14. General Procedure of Analysis

15. Flow Chart Geometry & Soil Properties & Element Properties Mesh Generation Initial Conditions Pore Pressure Condition K0-condition Staged Construction Geometry Configuration Water Pressures Update Mesh Running Results

16. Geometry & Soil Properties & Element Properties

17. Geometry & Soil Properties & Element Properties Mesh Generation

18. Geometry & Soil Properties & Element Properties Mesh Generation Initial Conditions K0-condition Pore Pressure Condition

19. Geometry & Soil Properties & Element Properties Mesh Generation Initial Conditions Pore Pressure Condition K0-condition Staged Construction

20. Geometry & Soil Properties & Element Properties Mesh Generation Initial Conditions Staged Construction Geometry Configuration Water Pressures

21. Results: Deformed Mesh (x100scale)

22. Results: Total Displacement

23. Results: Effective Normal Stress

24. Results: Horizontal Disp of Sheet Pile

25. Results: Shear Forces on Sheet Pile

26. Comparision: Lateral Earth Pressure

27. Comparision: Shear Force Dist.

28. Comparision: Bending Moment Dist.

29. Comparision: Summary of the Results • Results of the analyse and the hand-calculations are different because of: • “Staged Construction” in Plaxis • Assumption of Trapezoidal Lateral Earth Pressure • Total stress+pore pressure/effective stress+pore pressure Limitation of “Design Pressure Distributions” • Plaxis based on E on elastic range acc. to MC yield criteria

30. Analysis in Plaxis Flow

31. PLAXIS Flow Input: Steady-State Flow Screen (Impervious element)-sheet pile

32. PLAXIS Flow Staged Cons: Geometry

33. PLAXIS Flow Staged Cons: Geometry

34. PLAXIS Flow Staged Cons: Geometry

35. PLAXIS Flow Staged Cons: Geometry

36. PLAXIS Flow Staged Cons: SteadyState

37. PLAXIS Flow Staged Cons: SteadyState

38. PLAXIS Flow Staged Cons: SteadyState

39. PLAXIS Flow Staged Cons: SteadyState

40. PLAXIS Flow Results: Flow Field

41. PLAXIS Flow Results: GW Head

42. PLAXIS Flow Results: Pore Pressure

43. PLAXIS Flow Results: Deg. of Saturation

44. PLAXIS Flow Results: Flow Discharge

45. THANKS FOR YOUR ATTENTION… Any question ?