Lateral Loading of Suction Pile in 3D

Lateral Loading of Suction Pile in 3D Buoy Chain Sea Bed Suction Pile Integrated Solver Optimized for the next generation 64-bit platform Finite Element Solutions for Geotechnical Engineering

00 Overview This tutorial identifies the soil structure interaction by analyzing construction stage of 3D suction pile. It is possible to review in detail the stress distributions on cross-sections, which is not possible in D models. Also, interface is added between ground and pile to simulate the ground-structure interaction more realistically. The evaluation of the soil-structure behavior is done by using shell elements, not by simple rigid elements. Lastly, the tutorial will compare the results to a plaxis 3D tutorial.

0 Material & Property Ground Name Clay [unit : kn, m] Material Isotropic Model Type Mohr-Coulomb General Elastic Modulus (E) [kn/m ] 000 Inc. of Elastic Modulus [kn/m 3 ] 000 Reference level 0 m Poisson s Ratio (v) 0.35 Unit Weight (γ) [kn/m 3 ] 0 Ko 0.5 Porous Unit Weight (Saturated) [kn/m 3 ] 0 Drainage Parameters Undrained B Non-Linear Cohesion (c) [kn/m ] 5 Inc. of Cohesion [kn/m 3 ] 4 Reference level 0 m Frictional Angle (Φ) [deg] 0 3

0 Material & Property Structure [unit : kn, m] Name Steel-Pile Name Steel-Pile Material Isotropic Property D Model Type Elastic Model Type Shell Elastic Modulus (E) [kn/m ] e+07 Thickness 0.05 Poisson s Ratio (v) 0.3 Unit Weight (γ) [kn/m 3 ] 78 Interface Name Outer Interface Inner Interface Type Plane Shell Wizard Plane Shell Wizard R (Strength Reduction Factor) 0.7 tv (Virtual Thickness) 0. 0. Seepage Flow (m/sec/m) 0.003 0.003 4

0 Material & Property You can start the tutorial by opening a new file and setting the analysis settings to 3D and units to kn / m / sec Menu > New 5

0 Material & Property Define materials and properties from tables in previous slides Mesh > Material > New > Isotropic Define the materials from table. Clay Select Porous > Drainage Parameters > Undrained (Effective Stiffness / Undrained Strength). Steel-Pile Activate Structure Box for Steel Pile 6

0 Material & Property Define materials and properties from tables in previous slides Mesh > Property > Create Define the the properties Clay is 3D Shell is D with 0.05m thickness 7

0 Geometry Modeling Geometry > Surface & Solid> Box -Origin: (-30, 0, -30) - Width X = 60 - Width Y = 30 - Height = 30 Change Work Plane to X-Y Draw Circle Face Location (0,0,0) Radius (.5m) Check On Make Face 3 8

0 Geometry Modeling Geometry Protrude> Extrude - Select: Circle Face - Direction: Z-axis - Method: Length - Distance: -0 - OK Geometry > Boolean > Solid - Target : Soil Block - Tool: Pile Cylinder - OK 9

0 Geometry Modeling Geometry > Transform > Mirror -- Select: soilds - Plane: XZ-Plane (as shown in the figure) - Copy - Ok 0

03 Mesh Generation Mesh > Generate > 3D - Auto-Solid tab - Select: both cylinders - Size: - Tetra Mesher - Property: clay - >> Higher Order Elemet - Mesh Set: inner soil - Apply - Select: both soil soilds - Size: 3.75 - Tetra Mesher - Property: clay - Mesh Set: Outer soil - >> Higher Order Elemet - Apply

03 Mesh Generation Mesh > Element > Extract - Geometry tab - View Toolbar: Top -Type: Face - Select: the 6 side and top faces where the pile will be modeled - Property: Pile Wall - Mesh Set: Pile - OK - Measure 7m down the right side of the pile shell. - Draw 3D point at (.5, 0, -7)

03 Mesh Generation Mesh > Element > Interface - Plane tab - View Toolbar: Front - Type: From Shell - Select: all the wall elements - Direction: Negative Normal - Merge Nodes: Check on - Select: all the bottom nodes of pile elements (as shown in the figure) - Property Parameters: Wizard - Strength Reduction Factor(R): - Virtual Thickness (tv) 0. - OK - Create Rigid Link Element: Check on - Mesh Set: - Inner Interface Apply - REPEAT for Outer Interface using R = 0.7 (next slide) 3

03 Mesh Generation Mesh > Element > Interface - Plane tab - View Toolbar: Front - Type: From Shell - Select: all the wall elements - Direction: Normal - Merge Nodes: Check on - Select: all the bottom nodes of pile elements (as shown in the figure) - Property Parameters: Wizard - Strength Reduction Factor(R): 0.7 - Virtual Thickness (tv) 0. - OK - Create Rigid Link Element: Check on - Mesh Set: Outer Interface - OK 4

03 Mesh Generation The interface material can be defined using the following equation. Using the stiffness of adjacent elements and nonlinear parameters, the virtual thickness (tv) and strength reduction factor (R) is applied. Interface material stiffness and parameters are applied differently according to the relative stiffness difference between neighboring ground and structural members. The Wizard can be used to simplify this process. The general Strength reduction factor for structural members and neighboring ground properties are as follows. Checking the Element size consideration calculates the interface material properties considering the average length(line), average area(face) of the neighboring ground element when creating an interface. In other words, the average length(l), average area(a) are multiplies to the virtual thickness in the equation below to calculate the tangent, normal direction stiffness of the interface. If the consideration is not checked, the unit length(area) is applied. The thickness is defined separately for a line interface. The thickness is an important element when using the interface on a ground material that displays hardening behavior. Generally, the neighboring ground particle size is input, but if an accurate numerical value is not available, the default value from the program is used. For a 3D model, like the in the example above, the surface interface does not need a thickness. When defining the stiffness against seepage for an interface element, the permeability coefficient can be defined to be the same as the permeability coefficient of the ground. If the option is not checked, the layer is considered to be impermeable. 5

04 Analysis Setting Show all mesh sets. Static/Slope Analysis > Boundary > Constraint - Auto tab - Boundary Set: Ground support - Apply 6

04 Analysis Setting Show all mesh sets. Static/Slope Analysis > Load > Self Weight - Gz: - - Load Set: Self weight - OK 7

04 Analysis Setting Show only the Pile mesh set. Static/Slope Analysis > Load > Pressure - Face tab - View Toolbar: Front - Object Type: Node - Select: the highlighted point (as shown in the figure 7m below top on right side) - Direction Type: Coordinate X: 949 kn Z :5 kn - - Load Set: 30 degrees - OK 8

04 Analysis Setting Show all mesh sets. Static/Slope Analysis > Construction Stage > Stage Set - Add 4 cases - Stage Name: Initial - Select the highlighted mesh, boundary and load sets. Drag and drop them into Activated Data from Set Data. - Show Data: Activate - Define Water Level: 50 m - Clear Displacement: Check on - Save

04 Analysis Setting - New - Stage Name: Pile - Select the highlighted mesh sets. Drag and drop them into Activated & Deactivated Data from Set Data. - Save 3

04 Analysis Setting - New - Stage Name: 30 degrees - Select the highlighted mesh set. Drag and drop it the 30 degrees load - Activate Analysis Control -Allow Undrained Material Behavior - Set 0 Load Steps - Every Increment -- Save - Repeat 3 times for the other Construction Stage sets by making Copies and replacing the last stage with the corresponding load. 4

04 Analysis Setting Analysis > Analysis Case > General - Title: 30 Degrees - Solution Type: Construction Stage - Analysis Control - Initial Stage for Stress Analysis: Check on - Initial Stage: : Initial - Apply K0 Condition: Check on - OK Automatically consider Water Pressure: Check on -- OK Analysis > Analysis > Perform - Analysis Case: Check on - OK 5

05 Results 30 Degrees > Increment 0 > Displacement > TOTAL TRANSLATION (V) Activate only half soil of the mesh sets Results > Show/Hide > Min/Max Result > General > Smooth: Fringe Result > General > Deform: Undeformed Compare to results from plaxis tutorial Loading of Suction Pile for same load stage. Plaxis 6

05 Results 30 Degrees > Increment 0 > Displacement > TOTAL TRANSLATION (V) Select Iso Value Surface option Set Capped Style Upper Part Limit to mm 7

05 Results 3 30 Degrees > Increment 0 > Displacement > TOTAL TRANSLATION (V) Results > Advanced > Extract 3 Select Analysis Set: 30 Degrees Results: Total Translation Select All Nodal Results Extraction: Maxiumum Click Table 3 Select Step Value and Displacements Show Graph 8

05 Results 3 30 Degrees > Increment 0 > Displacement > TOTAL TRANSLATION (V) Rotate Model as shown Check On Multi Step Animation Recording Click Steps and Select All OK 3 Click Save to create animation. You can edit Animation in Properties drop down window menu 9

05 Results 30 degree load > Shell Element Forces > Axial Forces XX 30 degree load > Shell Element Forces > Moment YY 30 degree load > Interface Stress > Normal X Friction force between pile and ground 3 30

05 Results 40 Degrees > Displacement > TOTAL TRANSLATION (V) Activate only half soil of the mesh sets Results > Show/Hide > Min/Max Result > General > Smooth: Fringe Result > General > Deform: Undeformed 40 degree load > Shell Element Forces > Axial Forces XX 3 3 40 degree load > Shell Element Forces > Moment YY 3

05 Results 50 Degrees > Displacement > TOTAL TRANSLATION (V) Activate only half soil of the mesh sets Results > Show/Hide > Min/Max Result > General > Smooth: Fringe Result > General > Deform: Undeformed 50 degree load > Shell Element Forces > Axial Forces XX 3 3 50 degree load > Shell Element Forces > Moment YY 3

05 Results 60 Degrees > Displacement > TOTAL TRANSLATION (V) Activate only half soil of the mesh sets Results > Show/Hide > Min/Max Result > General > Smooth: Fringe Result > General > Deform: Undeformed 60 degree load > Shell Element Forces > Axial Forces XX 3 3 60 degree load > Shell Element Forces > Moment YY 33

06 Conclusion This tutorial was based in part on PLAXIS Tutorial: 3D Loading of Suction Pile Plaxis only models half of the shape, not the full pile and ground. modeled full 3D geometry. has more CAD import capabilities as well as more geometry CAD based commands for more accurate modeling. Plaxis used a RIGID BODY Object instead of Shell Element for the Pile. It has no structural properties, therefore it can t give any structural results like forces or moments like does. Plaxis used a HELPER Object for local mesh refinement. has more options for mesh refinement during and before meshing including command Mesh Size Control. has more options in post analysis results inspection including animation of construction process, on curve diagrams, results extraction/graphing, 3D pdf report, iso value surfaces. 34

Thank you! 35