0 2 4 6 8 10 12 14 16 FL AC Pl ax Ab is aq G eo us -s Sa lop ge e cr is p Ad in a O as VI ys Finite Element Packages SAN G O E LI N A F AN E SY S so fis to tik ch n FE og FL O Aq W ua M 3D od Fl o Ec w lip se Z M _so O D il U LE F
Finite Element Packages engineering/consultancy office FLAC Plaxis Abaqus Geo-slope Oasys Others research institute university contractor
Background Developed at the Technical University of Delft for Dutch DPWWM Initially was intended to analyze the soft soil river embankments of the lowlandsof Holland Soon after, the company Plaxis BV was formed, and the program was expandedto cover a broader range of geotechnical issues
What is PLAXIS????? FEM package - for analysis of deformation and stability Requires advanced constitutive models for the simulation of the non linear,time dependent and anisotropic behaviour of soils and/or rock. Since soil is a multi phase material, special procedures are required to dealwith hydrostatic and non hydrostatic pore pressures in the soil. Although the modelling of the soil itself is an important issue, many projectsinvolve the modelling of structures and the interaction between the structuresand the soil. Plaxis is equipped with features to deal with various aspects of complexgeotechnical problems.
PLAXIS Features Input Features Soil Behaviour Interfaces Excess pore water pressure Geogrids Groundwater flow analyses Anchors Steady state pore pressure Boundary conditions User-defined soil models Tunnels Advanced soil models Loads Mohr-Coulomb model Hinges and rotation springs Hardening soil model Plates Soft soil creep model High-order elements Material set database Automatic mesh generation Soil tests Graphical input of geometry models
PLAXIS FeaturesCalculation features Output features Consolidation Analysis Velocities and accelerations Staged construction Load displacement curves & stress paths Calculation Manager Animations Safety factors Report generator Updated Lagrangian analyses Cross-sections Arc-Length control Structural forces & Displacements Automatic load stepping Stresses Parameter Variation Deformation Presentation of results Stress paths
PLAXIS Analysis Get familiar using Plaxis Step I • Define the model • Input geometry + structural elements; • Apply boundary conditions; • Apply loading and/or prescribed displacements; • Enter material properties; • Mesh generation;
PLAXIS Analysis Step II • Initial flow and boundary conditions; • Generation of initial pore water pressures; • Define initial stress state; Step III • Calculation Step IV • Output
PLAXIS Usage engineering/consultancy office Embankment Trench & excavations gravity walls reinforced/anchored earth wall embedded walls shallow/ surface foundations deep foundations tunnels water flow others (soil dynamics,…) research institute university contractor
PLAXIS Usage engineering/ Back calculation consultancy office Full design: ULS calculations Full design: SLS calculations Validation of results obtained from analytical methods Research applications Others (...) research institute university contractor
PLAXIS Usage engineering/ Discretisation consultancy Type of elements office Boundary conditions Initial conditions Choice of soil model Choice of type of analysis Parameters determination Results interpretation Others (calculations for ULS...) research institute university contractor
Validation of Results engineering/ parametric study consultancy office comparison with results obtained from an analytical approach comparison with examples from literature experience Others (monitoring…) research institute university contractor
Why use PLAXIS? Easy and user friendly? Versatile and flexible? (you or PLAXIS) Required? Advantage? Value adding or adding value? Familiar?
When to use PLAXIS? Easy? Required? Advantage? Value adding or adding value? Familiar?
Example……Island Cut MethodInnovative Slope Stabilisation Measure (EQ-Performance Based Design)
Issues……. Feel for results? Time? Knowledge? Verification? Problem identification? Appropriate model?
Solution……. 1. Crude estimation – feel for results 2. Assessment details verified – plane strain/axisymmetric? 3. Model verified – dimensions, elements and boundaryconditions 4. Initial stress state verified – steady state or transientgroundwater, groundwater boundary condition, in-situ stressconditions 5. Staging verified – changes in dimensions, loadingconditions and load steps 6. Calculation type verified – plastic, consolidation or c-phireduction? 7. Output type specified -
In a nutshell……. PLAXIS is not a solution, but a tool, only if used appropriately. FEM can be too complex and too costly. The lead engineer need to know whether FEM is really requiredor not. The lead engineer need to make sure adequate verification isdone on the input before analysis is being carried out. The engineer should have crude calculation/solution/results inhand BEFORE running PLAXIS. In many projects, LEM is what really required. Generally, simple analytical solutions (LEM) would suffice. Try to avoid doubling the the time and effort – its a waste.