Wick Drains
1.0 Introduction
This tutorial introduces the Wick Drain feature in RS3. Wick drains are installed in soil to improve the rate of seepage when placed to speed up consolidation. In the tutorial, we cover how wick drains are used in the coupled transient analysis model that involves construction of embankment over the stages and also take into account the traffic loading. The modeling results show the effect of wick drains based on the change in pore water pressure and total head distribution.
2.0 Starting the Model
- To start the tutorial, select File > Recent > Tutorials Folder in the main menu.
- Open the starting file Embankment Consolidation-no wick drain.rs3v3.
- To show all geometry, select View > Show Intersected Geometry.
2.1 PROJECT SETTINGS
We'll start by checking that the project's Groundwater and Stages settings are set up appropriately.
- Select Analysis > Project Settings
- Select the Groundwater tab to view Method = Transient settings.
- Select the Stages tab to view how the staging is set up.
2.2 MODEL DESCRIPTION
2.2.1 Embankment Construction
The model is designed such that the embankment is constructed by layer over nine stages (Stage 1 - Stage 9). The embankment is divided into four entities that have staged material properties. All four entities have no material property assigned (Applied Property: No Material) at Stage 1. Sequentially, the model is designed in order that the material property named as Embankment Fill is assigned to the embankment entities every other stage from the bottom layer (Stage 3) to the top (Stage 9).
For instance, Stage 1 represents initial condition before embankment construction, as shown below:
In Stage 9, the model has all embankment entities assignment with Embankment Fill property, representing completed construction of embankment:
2.2.2 Applying Surface Load
In Stage 11, a surface load of 10 kPa is applied on the top surface of the embankment to represent the load applied by the traffic.
You can check this by switching the workflow tab to the Load workflow tab , wherein the applied surface load will be automatically selected.
2.2.3 Groundwater
Select the Groundwater workflow tab , as this section describes the groundwater boundary condition applied to the model.
Total Head of -12 m is applied on the left and right face of the soil foundation (represented by Intermediate Layer entities) while an unknown boundary condition is applied on the top surface.
As the embankment is constructed with the stage advancement, the unknown boundary condition is updated accordingly, as such that it is removed and re-applied to cover solely the surface of the embankment.
- Switch to the Selection tab under Visibility Pane.
- Select any combination of items.
- Clicking the Add a New Selection Group icon under Selection tab.
For this tutorial, the Selection group is made for the faces of the top surface of the intermediate layer that is not covered by the embankment to repeat adding the Unknown groundwater boundary condition.
2.2.4 Meshing and Restraints
Additional steps in creating the model include:
- Defining the mesh refinement region using the box with the uniform element size of 1.5 m.
- Meshing the model with uniform element size 2 m.
- Applying restrains to fix in x and y direction and all direction on the side surfaces and bottom surface of the foundation, respectively.
3.0 Adding Wick Drains
This section explains the procedure to install wick drains. In this model, wick drains are added in Stage 2.
- Select the Groundwater workflow tab
- Select Intermediate Layer entities from the Visibility Tree.
- Right-click and select Hide All but Selected Geometry.
- Select: Edit > Selection Mode > Faces Selection
and select the faces below the embankment or under Visibility pane, switch from Visibility Tree to Visibility Selection and select Wick Drain group, which already has those surfaces grouped.
- Go to Groundwater > Add Wick Drain Region. The Polyline dialog will pop up.
- Under the Plane Options enter XY Orig = (0, 0, -5).
- Click Edit Table under Coordinate Input and copy/paste the coordinates below or draw a polyline following the edge of the selected surface (highlighted in orange).
UV33.93602 34.37565 50 35.35914 65 38.08641 70 37.17732 80 38.08641 80.66866 38.11681 80.66866 11.88319 80 11.91359 70 12.82268 65 11.91359 50 14.64086 33.93602 15.62435 33.93602 34.37565 - A Wick Drain/Relief Well Options dialog will appear. Enter the following:
- Spacing: X = 4, Y = 4
- Grid Origin: X = 52.248, Y = 26.892, Length = 20
- Wick Drain/Relief Well Properties:
- Type = Wick Drain
- Pressure Type = Pressure
- Pressure = 0, Diameter = 0.1
- Equivalent Permeability = 0.001
- Type = Wick Drain
- Install at Stage 2
- Remove at Stage 12
- Spacing: X = 4, Y = 4
4.0 Compute
- Select the Compute workflow tab
- From this tab, we can compute the results of our model. Before commencing the stress analysis computation, it is recommended to save the final model as a separate file so that you can access the original file anytime: File > Save As.
- Select Compute > Compute
5.0 Results
- Select the Results workflow tab
The role of wick drain is to increase the rate of seepage to reduce the consolidation time. Therefore, it casts direct impact on pore pressure and vertical displacement as a suitable indicator to monitor the consolidation settlement. The performance of wick drains can be visualised by placing a contour plane intersecting the wick drains. - Select: Interpret > Show Data on Plane > XZ Plane
- Enter the origin location/orientation of the plane as following:
- X1 = 50, Y1 = 23, Z1 = -20
- Orientation (X, Y, Z) = 0, 1, 0
- X1 = 50, Y1 = 23, Z1 = -20
- Add YZ contour plane with following location/orientation:
- X1 = 48, Y1 = 25, Z1 = -20
- Orientation (X, Y, Z) = 1, 0, 0
- X1 = 48, Y1 = 25, Z1 = -20
5.1 Pore Water Pressure
- In the Legend, select the Seepage > Total Pore Water Pressure contour plot.
- Click Contour Options
and Reduce the Interval Count to 20 and with Show Contour Lines enabled.
Total pore water pressure distribution for Stage 1, Stage 2, Stage 8 and Stage 14 are presented in the figure below. The modelling results show that along the length of the wick drain, the pore water pressure remains close to or less than 0 kPa.
5.2 Total Head
- In the Legend, select the Total Head contour plot.
- Click Contour Options again. We will keep the same contour options as pore water pressure (20 intervals and showing contour lines). However, for total head, we will use the Contour Range = Auto Range (All Stages) option (which only becomes enabled after loading the total head contour plots for all stages).
Total pore water pressure distribution for Stage 1, Stage 2, Stage 8, and Stage 14 are presented in the figure below. The modelling results show a significant reduction in total head around the regions with wick drains installed.
5.3 Z Displacement
- In the Legend, select the Z Displacement contour plot.
- Adjust the Contour options as following:
- Contour Range = Auto Range (All Stages)
- Interval Count = 20
- Colour Table = Cold to Hot
- Show Contour Lines = Enabled
- Contour Range = Auto Range (All Stages)
The Z displacement contour plot shows the settlement progression with respect to time.
The magnitude of settlement can be quantitatively compared between stages by using the query point and plotting a z displacement-time graph. To obtain the graph, the following steps needs to be executed:
- Select Interpret > Queries > Add Line Query.
- On the Draw Polyline Pane, enter coordinate point 65, 26, -5.2 for X, Y, Z and click Enter.
- Click Done.
- Select the created Query Line entity from the visibility tree.
- Select Interpret > Graph Data or click the Graph Data icon in the toolbar.
- Under Chart Options select [Change Plot Data...]
- The Chart Options dialog will appear. Keep the Primary Data = Total Displacement [m], switch Horizontal Axis = Stage Time [Days], and check all stages other than the first three. Click OK.
- Under Settings, enable the Logarithmic X-Axis option and enter:
- Min X Value: 13
- Max X Value: 2640
- Min Y Value: -0.14
- Max Y Value: -0.05
Following the above-mentioned procedures, the Stage Time [Days] - Z Displacement [m] graph should be generated as below: