Plaxis triaxial test

Plaxis triaxial test .

1 Simple modeling of standard laboratory tests with PLAXIS Version 8 To model standard laboratory tests with PLAXIS 8 a simple (axisymmetric) model of 1x1 m 2 without gravity stresses can be used. Underneath an example is given of the modeling of a triaxial test. File > General settings: The geometry model is constructed as follows: Geometry > Geometry line: (0;0) > (1;0) > (1;1) > (0;1) > (0;0) Loads > Vertical fixities: (0;0) > (1;0) Loads > Horizontal fixities: (0;0) > (0;1) Loads > Distributed load system A: (0;1) > (1;1) > (1;0) 2 Update By default, distributed loads have a unit value which are pointing towards the model. In this case the initial value must be set to the confining pressure (for example -100 kN/m 2 ). This can be done by double-clicking the geometry line at which the load is acting (use the selection tool); subsequently select 'Distributed load (system A)' from the selection window and enter -100 for both y-values. Do this for both geometry lines with distributed loads. Materials > Soil & interfaces: Create a new data set and enter the model parameters listed at the end of this section. 'Drag' the data set to the geometry model and 'drop' it on the cluster. The geometry model should look as follows: Press the 'Generate mesh' button to generate the finite element mesh and subsequently press to return to the input program. 3 Define Update Update Update Calculate Output Initial conditions Calculate Define Press and accept the standard unit weight for water (10 kN/m 3 ). Subsequently, press (initial pore pressures and effective stresses should remain zero in this simple modeling). Save the input under an appropriate name (for example 'Triax'). After a few seconds the Calculations program is started. In the Calculations program, four calculation phases should be defined: Phase 1: Isotropic compression General: Calculation type: Plastic Parameters: In a CU-test, this phase can be considerd drained. If the material data set is 'Undrained', this can be achieved by selecting the option 'Ignore undrained behaviour' te selecteren. Loading input: Staged Construction > In the Staged Construction window, activate the distributed load and see if the load at both lines is still -100 kN/m 2 > Phase 2 - 4: Axiale loading General: Calculation type: Plastic Parameters: To let the displacements and strains start from zero, select only in Phase 2 the option 'Reset displacements to zero'. Loading input: Staged Construction > In the Staged Construction window, increase the axial load by -100 kN/m 2 to -200 kN/m 2 (ph.2), -300 kN/m 2 (ph.3), -400 kN/m 2 (ph.4) respectively. The horizontal load remains equal to the confining pressure > Press the button 'Select points for curves' and subsequently press the button 'Select stress points for stress/strain curves'. Select (an) arbitrary stress point(s) in the middle of the mesh. At these points the stresses and strains will be stored for stress-strain curves. Subsequently press Back in the Calculations program, press to start the calculations. After the calculation, press to view the results of the final calculation step. After viewing the results of the final step, press the Curves icon (upper left corner). In the Curves program, select for the x-axis: Strain (point: A; type: ε 1 ) and for tye y-axis: Stress (point: A; type; q). Soil tests: Plaxis version 8.4 has a convenient option to run simple soil tests (triaxial, oedometer) on the basis of defined material data sets using a single stress point algorithm. This option is available in the material data base of the Plaxis 8.4 Input program (V.I.P version). 4 Example of data set with Mohr-Coulomb model parameters: (The tab-sheet 'interfaces' is not relevant) 5 Example of data set with Hardening Soil model parameters: 6 Sand test.vlt eps_1 0 -0.01 -0.02 -0.03 -0.04 -0.05 -0.06 -0.07 -0.08 |sig_1 - sig_3| [kN/m²] 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 Results (using soil tests): Note: E 50 is equal for both models! Sand Mohr circle and Coulomb envelope sig [kN/m²] 0 -30 -60 -90 -120 -150 -180 -210 -240 -270 -300 tau [kN/m²] 180 150 120 90 60 30 0 HS MC . 1 Simple modeling of standard laboratory tests with PLAXIS Version 8 To model standard laboratory tests with PLAXIS 8 a simple (axisymmetric) model of 1x1 m 2 without gravity. and for tye y-axis: Stress (point: A; type; q). Soil tests: Plaxis version 8.4 has a convenient option to run simple soil tests (triaxial, oedometer) on the basis of defined material data. without gravity stresses can be used. Underneath an example is given of the modeling of a triaxial test. File > General settings: The geometry model is constructed as follows: