Example Application 4. Undrained Cylindrical Cavity Expansion in a Cam-Clay Medium

Transcription

1 Example Application 4 Undrained Cylindrical Cavity Expansion in a Cam-Clay Medium 1

2 Cylindrical Cavity Model Geometry 2

3 Saturated Clay Properties Cam-Clay Model 3

4 Modeling Procedure Step 1 Step 2 Step 3 Create a cylindrical cavity model using the axisymmetric configuration. Assign the Cam-Clay material model and properties. Set boundary and initial stress conditions. Input Cam-Clay properties that are stress dependent. Apply cavity expansion and monitor stress and pore pressure change. 4

5 In the [Model options] dialog, select [Axisymmetry] and [GwFlow] configuration options, and [Include advanced constitutive models] user interface option. The system of units are [SI: meter-megagram-second]. 5

6 A project title is assigned, and a project file cavity.prj is created and stored in a working directory. 6

7 Step 1-1 In the [Geometry Builder] create a rectangular box with boundaries at Xmin = 1.0, Xmax = 100.0, Ymin = 0.0, Ymax =

8 Step 1-2 In the [Blocks] edit stage check that the model contains one quad block. Press [OK] to exit the [Geometry builder] 8

9 Step 1-3 Enter the [Virtual]/[Edit] tool and select the [Mesh] edit stage. Uncheck [Use automated zoning]. Input the mesh size for the model (i=31,j=1), as shown. 9

10 Step 1-4 Check [Adjust ratio] and set Ri = 1.1, Rj = 1.0. Press [OK] and then [Execute] to send the commands to FLAC. 10

11 Step 1-5 Check the commands in the Record pane. 11

12 Step 1-6 Enter the [Material]/[Models] tool. Select [cam-clay] plastic model and then press [Set all] to open the Model cam-clay properties dialog. Input the Cam-Clay properties, as shown. Press [OK] and then [Execute] to send the commands to FLAC. 12

13 Step 1-7 Enter the [In Situ]/[Fix] tool. Select [Fix] mode and [All] range and click on [Y] GP velocity type. Roller boundaries are then applied on top and bottom of model. 13

14 Step 1-8 Select [Fix] mode and [Rect.] range and click on [X] GP velocity type. Drag the mouse along the left boundary to fix movement in the x- direction. 14

15 Step 1-9 Enter the [In Situ]/[Initial] tool and select [GPs] and [xvelocity]. Drag the mouse over the left boundary gridpoints and the x-velocity dialog opens. Input the value of 1.0e-5. This will apply a constant value of 1.0e-1 because this is a fixed velocity gridpoint. 15

16 Step 1-10 Enter the [In Situ]/[Apply] tool and d=select [Stress]/[pressure] Drag the mouse over the right boundary gridpoints and the Apply value dialog opens. Input the pressure =

17 Step 1-11 Enter the [In Situ]/[Initial] tool and select [All]. Click on [sxx] and press [Assign]. When the xx-component of stress dialog opens, input a value of Repeat this procedure for [syy] and input a value of Repeat this procedure for [szz] and input a value of Press [Execute] to send these commands to FLAC. 17

18 Step 1-12 Enter the [Settings]/[GW] tool and uncheck [<flow> groundwater calculation]. Enter the [Settings]/[Mech] tool and check [Large-strain]. 18

19 Step 1-13 Save the state as cav1.sav. 19

20 Step 2-1 Enter the [Fish] pane. The FISH function set_prop.fis inputs the Cam-Clay properties that are stress dependent. Execute the function. 20

21 Step 2-2 Return to the [Record] pane. The function set_prop is shown in a new branch. 21

22 Step 2-3 function. Enter the [Fish] pane again. The FISH function c_var calculates Cam-Clay parameters to monitor during the calculation. Execute the 22

23 Step 2-4 Enter the [Utility]/[History] tool. Add FISH histories c_var, c_a and c_q using the [Fish->History] button. 23

24 Step 2-5 Add histories for [sxx] and [pp] at gridpoint i=1,j=1. Press [Execute] to send the commands to FLAC. 24

25 Step 2-6 Save the state as cav2.sav. 25

26 Step 3-1 Enter the [Run]/[Cycle] tool and run the cavity expansion calculation for 100,000 cycles. 26

27 Step 3-2 Save the state as cav3.sav. 27

28 Step 3-3 Use the [Plot]/[History] tool to plot deviator stress versus a/a 0. 28

29 Step 3-4 Use the [Plot]/[History] tool to plot total radial stress and excess pore pressure at the cavity wall versus a/a 0. 29

30 Step 3-5 Enter the [Fish] pane. The FISH function b_table creates tables to plot stress and pore pressure results when a = 2a 0 plotted versus ln(r/a 0 ). Execute the function. 30

31 Step 3-6 Return to the [Project] pane and save the state as cav4.sav. 31