Example Application 15. Lined Tunnel Construction in Saturated Ground

Transcription

1 Example Application 15 Lined Tunnel Construction in Saturated Ground 1

2 Conditions and sequence for the lined tunnel construction 2

3 Modeling Procedure Step 1 Step 2 Step 3 Step 4 Create a circular tunnel. The geometry is symmetric about the tunnel center, permitting half the tunnel to be modeled. Assign the Mohr-Coulomb material model and properties for the rock. Set boundary and initial stress conditions. The site is dewatered and initially unsaturated. Calculate the initial equilibrium stress state. (Stage 1) Excavate the tunnel to produce closure corresponding to 30% relaxation before the shotcrete liner is installed. (Stage 2) Install the shotcrete liner and advance the tunnel to produce 100% relaxation. (Stage 3) Step 5 Install the concrete liner with a 1 cm gap. (Stage 4) Step 6 Stop dewatering and allow water level to return to original level. Water exerts a pressure in the gap between the two liners. (Stage 5) Step 7 Delete the shotcrete liner, simulating degrading of the shotcrete. (Stage 6) 3

4 In the [Model options] dialog, select [GwFlow] and [Adjust tot. stress] configuration options, and [Include structural elements] user interface option. The system of units are [SI: meter-kilgram-second]. 4

5 A project title is assigned, and a project file linedtunnel.prj is created and stored in a working directory. 5

6 Step 1-1 In the [Geometry Builder] create a rectangular box with boundaries at Xmin = 0.0, Xmax = 120.0, Ymin = -80.0, Ymax =

7 Step 1-2 Select [Circle] and locate the tunnel at Xc = 0.0, Yc = 0.0, with Radius = 6.0 and Segments = 32. Press [OK] to generate the circle. 7

8 Step 1-3 Select [Delete edges] and click on the circle boundary segments outside the model to delete edges. 8

9 Step 1-4 Select [Add] and create a new line group named construction line. 9

10 Step 1-5 Using [Add edges/[box] draw a box around the tunnel. Add a box inside the tunnel and connect corners to form 4-sided blocks. 10

11 Step 1-6 Add additional construction lines to divide the model into quadrilateral blocks, as shown. A horizontal line is positioned at y=60, which is the location of the phreatic surface. 11

12 Step 1-7 Select [Blocks] to confirm the model is divided into 14 quad blocks. It may be necessary to use the [Cleanup] stage to produce the model filled completely with quad blocks. Press [OK] in the Result dialog, and then [OK] to exit the [Builder] tool. 12

13 Step 1-8 The model can now be edited. Select [Edit] to enter the [Edit] tool. 13

14 Step 1-9 Select [Boundary] and [Automatic boundary cond.] to place roller boundaries on the sides and fixed boundary on the base of the model. 14

15 Step 1-10 Select [Mesh]/Block elements] and [Rotate block IJ] option. Rotate the blocks around the tunnel to remove attached boundaries around the tunnel periphery. The rotated blocks axes should appear as shown, to remove attached edges around the tunnel. 15

16 Step 1-11 Select [Boundaries]/[Mark boundaries] and click on the tunnel boundary segments. 16

17 Step 1-12 Select [Mesh]/[Zone size manual] and click on the red boxes to increase the zone density around the tunnel, as shown. 17

18 Step 1-13 Change the zone density in blocks farther away from the tunnel, by clicking on the red boxes and manually changing zoning. Select [Adjust ratio] to increase the zone size by a geometric ratio of 1.1 in the i-direction, and 0.9 below the tunnel, 1.1 above the tunnel in the j-direction. 18

19 Step 1-14 Select [Material]/[Assign] and then [Create] to open the Define Material dialog. Create a material named ground as a Mohr-Coulomb material and assign properties, as shown. 19

20 Step 1-15 Press [Set all] to assign ground to all zones in the model. Press [OK] to exit the [Edit] tool. 20

21 Step 1-16 Press [Execute] to send the commands to FLAC. Press [Save] to save the state as initial.sav. 21

22 Step 2-1 Enter the [In Situ]/[Initial] tool and assign the initial stress state. 22

23 Step 2-2 Select the [Settings]/[Gravity] tool and input the gravitational magnitude, as shown. 23

24 Step 2-3 Select [Settings]/[GW] and turn off the groundwater flow calculation. 24

25 Step 2-4 Select [Run]/[Solve] and [Solve initial equilibrium as elastic model] to calculate the initial equilibrium state. Save the state as equilibrium.sav. 25

26 Step 3-1 Enter the [Material]/[Assign] tool. Select [Region]/[range] and then [null] and click on the zone region inside the tunnel to null the tunnel zones. 26

27 Step 3-2 Enter the [Fish editor] pane and open the FISH function vert_closure.fis. Vertical closure will be calculated between gridpoints i=39, j=19 (tunnel crown) and i=75, j=19 (tunnel invert). Execute the function, and press [OK] to return to the [Record] pane. 27

28 Step 3-3 Enter the [Utility]/[History] tool. Press [Fish->History] and select vert_closure. 28

29 Step 3-4 Press [Gridpoints]/[X components]/[xdisp] and select the gridpoint at the tunnel mid-point. Press [Execute] to send these commands to FLAC. 29

30 Step 3-5 Enter the [In Situ]/[Apply] tool. Select [Relax] and drag the mouse along the tunnel periphery. Press [Assign] to open the Apply relax dialog. Set number of steps = 20 and end factor = 0.7. Check [Generate Ground Reaction Table] and select history 1 to write to table 1. 30

31 Step 3-6 Use the [Run]/[Solve] tool to calculate the state at 30% relaxation. The tractions (forces) around the tunnel are shown above. Save the state as relax_30.sav. 31

32 Step 4-1 Enter the [Structure]/[Liner] tool and select [Add]. Drag the mouse along the tunnel boundary to create shotcrete liner segments attached to the grid. 32

33 Step 4-2 Enter the [Structure]/[SEProp] tool and assign material properties representing the shotcrete liner material. 33

34 Step 4-3 Enter the [Structure]/[Node] tool and [Fix]/[Rotation] for nodes 1 and

35 Step 4-4 Enter the [In Situ]/[Apply] tool and select [Relax]. Drag the mouse along the tunnel periphery and press [Assign]. Set the number of steps = 20, and the end factor = 0.0. Check [Continue] and [Generate Ground Reaction Table] to continue the ground reaction curve. 35

36 Step 4-5 Enter the [Settings]/[Mech] tool. Press [Large-strain] to continue the run in large strain mode. 36

37 Step 4-6 Use the [Run]/[Solve] tool to calculate the equilibrium state at 100% relaxation of the tunnel with shotcrete support. Save the state as relax_100.sav. 37

38 Step 5-1 Enter the [Structure]/[Liner] tool and select [Add] to install the concrete liner. Press [Attach nodes:]/[to an interface] and check [Add gap for grid] with distance = Drag the mouse along the tunnel periphery. An Interface properties dialog opens. Enter the properties for the liner/ground interface. (Normal and shear stiffness = 4 GPa/m, friction angle = 30 o.) 38

39 Step 5-2 Select [PropID] and change the liner property to L2. Press [Execute] to send the commands to FLAC. 39

40 Step 5-3 Enter the [Structure]/[SEProp] tool and assign the concrete liner properties, as shown above, to property L2. 40

41 Step 5-4 Enter the [Structure]/[Node] tool and [Fix]/[Rotation] and [X-velocity] to zero for nodes 38 and

42 Step 5-5 Use the [Run]/[Solve] tool to calculate the equilibrium state with the concrete liner installed. Save the state as concrete_liner.sav. 42

43 Step 6-1 Enter the [Settings]/[Mech] tool and turn off the mechanical calculation. Enter the [Settings]/[GW] tool. Turn on the groundwater flow calculation and set water density to 1000 kg/m3 and water bulk modulus to 10,000 Pa. 43

44 Step 6-2 Enter the [Material]/[GWProp/ tool and set porosity = 0.3 and permeability = 1e

45 Step 6-3 Enter the [Fish editor] pane. Open ININVT.FIS. Set wth = 60, k0x = 0.5, k0z = 0.5 and syytab = 0. For this setting (syytab=0) only the pore pressure distribution is calculated and total stress is adjusted from the CONFIG ats command. 45

46 Step 6-4 Use the [Run]/[Solve] tool to calculate the steady state groundwater flow state. The pore pressure distribution is plotted above. Save the state as water.sav. 46

47 Step 7-1 Use the [settings]/[gw] tool to turn the groundwater flow calculation off and set water bulk modulus to zero. Use the [Settings]Mech] tool to turn the mechanical calculation back on. 47

48 Step 7-2 Enter the [In Situ]/[Apply] tool and select [Stress]/[pressure]. Drag the mouse along the tunnel periphery and the press [Assign]. When the Apply value dialog opens, enter the pressure = Pa., and y-variation =

49 Step 7-3 Enter the [Fish editor] pane and open FISH function apply_gap_press.fis. Execute the function and assign y_wtab = 60, tuncen_x = 0.0 and tuncen_y = 0.0. Press [OK] and return to the [Record] pane. 49

50 Step 7-4 Enter the [In Situ]/[Initial] tool and press Clear? [Displmt&velocity]. 50

51 Step 7-5 Enter the [Utility/[History] tool. Press [Reset] and then reassign vert_closure and xdisp histories as done in Steps 3-3 and

52 Step 7-6 Calculate the equilibrium state using [Run]/[Solve]. Save the state as gap_pressure.sav. 52

53 Step 8-1 Enter the [Structure]/[Segments] tool. Check [Delete] and delete the shotcrete structural element segments. Be careful to not delete the concrete liner segments. 53

54 Step 8-2 Use the [Run]/[Solve] tool to calculate the equilibrium state with the shotcrete deleted. 54

55 Step 8-3 Save the state as delete_shotcrete.sav. 55