The Program and itsApplications by Ari Cohen Background •Developed at the Technical University of Delft for Dutch DPWWM •Initially was intended to analyze the soft soil river embankments of the lowlands of Holland •Soon after, the company Plaxis BV was formed, and the program was expanded to cover a broader range of geotechnical issues The Netherlands Getting Started PLAXIS is comprised of four interconnected but separate interfaces •Input •Calculations •Output •Curves Tutorial 1: The Modeling the Settlement of a Circular Footing on Sand . 1. Choose new or existing project . General Settings .2. 3. Plane Strain or Axisymmetry / 15-Node or 6-Node . Plane Strain or Axisymmetry .4. Plane Strain or Axisymmetry Cont. y x .4. 5. 15-Node or 6-Node . 15-Node or 6-Node Cont. .5. 6. Dimensions . . . Geometry Contour .7. Fixes the rotational degree of freedom of a beam . Convenient and fast input option for many applications • Tractions 1. Are actually line loads in the out-of-plane direction 2. Distributed loads applied to geometry lines 2. Special Conditions placed on geometry lines that control the displacement of the lines 2. Fixities take priority over displacements and other loads • Standard Fixities 1.8. Prescribed displacements equal to zero 2. Can be altered by double clicking on the geometry line associated with it • Point Forces 1. Input values given in the dimensions force per unit area 3. vertical. Can be altered by double clicking on the geometry line associated with it • Fixities 1. Drawn over geometry lines 3. Can be of horizontal. or total (horizontal & vertical) 3. Loads & Boundary Conditions • Prescribed Displacements 1. Can have vertical and horizontal components • Fixed Rotations 1. Select Standard fixities button 8. . Loads & Boundary Conditions cont. . Loads & Boundary Conditions cont.Select Prescribed displacement button 8. Geotextiles & 4. Modeling with the Mohr-Coulomb default requires the following five variables to be input: 1. (n) 3. There exist three types of soil models that PLAXIS supports: 1. Young’s modulus. (f) and 5. Material Properties • Database with material data sets 1. friction angle. (E) 2. dilatancy angle. Mohr-Coulomb model 2. Soil properties and material properties of structures are stored within the database as four types of material sets 1. Poisson’s ratio. Mohr-Coulomb is most often used as good soil data is not always available to the engineer or scientist 3. (c) 4. Hardening-Soil model & 3.9. Soft-Soil-Creep model 2. Beams 3. Soils & Interfaces 2. (y) . Anchors • Modeling of Soil Behavior 1. cohesion. 9. Material Properties cont. • All clusters and structural elements in a given model must be assigned a material before a mesh can be generated • The following soil parameters will be used for the footing settlement example: . .Click Materials button 9. Material Properties cont. Select “New” material 9. Material Properties cont. . Select Enter given “New” data material . Material Properties cont.Type “sand” and leave the other default inputs 9. . Material Properties cont.Enter Select given data “New” and material click Ok 9. .Drag & Drop the “Sand” material into the cluster 9. Material Properties cont. This can be accessed by double clicking on any geometry point • Local Refinement Instead of adjusting the “Local element size” factor.10. and Very fine. Coarse. one step per selection • Local Coarseness In areas where it may not be necessary to have a very refined mesh. Number of mesh elements generated ranges from about 50 elements for the coarse setting to about 1000 elements for the very fine setting • Global Refinement Automatically generates a refined mesh. Medium. Mesh Generation • Global Coarseness Distinction is made between five levels of global coarseness: Very coarse. Fine. or points can be selected and the local refinement option can be used . lines. clusters. the mesh may be made more coarse by adjusting the “Local element size” factor for a particular geometry point. Select “Generate mesh” Once the mesh window appears select “Update” 10. Mesh Generation cont. . A default value is given based on Jaky’s formula (1-sinf). Clicking on a particular element in this mode determines if it will be on or not 2. The stress state is generally characterized by an initial vertical stress. the “Initial conditions” must be inputted. Water Weight: In projects that involve pore pressures. the generate water pressures button is selected to complete the water conditions process • Geometry Configuration mode 1. With a phreatic line it is understood that water pressures above the line are zero and increase linearly with depth below the line. Initial Stress Generation (K0-Procedure): Initial stresses in a body are influenced by the weight of the material and the history of its formation.0 which is related by the coefficient of lateral earth pressure K0. There are two different modes within the initial conditions tab: Water conditions mode and the Geometry configuration mode • Water Conditions mode 1. the input of water weight in necessary to distinguish between effective stresses and pore pressures.11. PLAXIS default water weight is set to 10kN/m3 2. These elements must be deactivated in this mode. . Water Pressure Generation: After a phreatic line or groundwater boundary conditions are specified. Groundwater Flow: In addition to generating water pressures using a phreatic line. Initial Conditions • Once the geometry model has been created and the mesh has been generated. This requires the input of groundwater head boundary conditions 4. The phreatic line can be a general or user defined type 3. Deactivating Geometry Components: In projects where embankments and structures are to be constructed the geometry model will have some elements that are initially not active. Phreatic Lines: Pore pressures and external water pressures can be generated on the basis of phreatic lines. By default PLAXIS activates all elements of the model outlined in the previous geometry setup stage. sn. water pressures can also be generated using groundwater flow calculations. . Initial Conditions cont. Water levels will not be generated in this example so proceed to generate initial stresses 11.1.Select “Initial conditions” button and accept default water weight 2. .Accept default K0 parameters 11. Initial Conditions cont. Length of lines note relative magnitude of principal stresses Orientation of lines note principal direction 11. . Initial Conditions cont. Initial Conditions cont. .Finally it is time to proceed to the Calculation phase of the program 11. Questions? .