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MSE Wall Design (with .x30 Criteria)

Federal Lands Highway has a variety of retaining walls available within the FLH criteria library. The basic design and layout of these walls are all very similar. I will attempt to illustrate a step by step procedure for designing what we refer to as a MSE (Mechanically Stabilized Earth) Wall, a wall commonly used here in Western Federal Lands Highway.

An example of a typical MSE Wall (including a description of the wall adhoc attributes) is shown below:

Adhoc Name: Description:
Wall Foreslope Slope of the wall foreslope, expressed in rise:run.
Wall Batter Slope of the face of the wall, expressed in rise:run.
Leveling Pad Depth Depth for optional leveling pad, expressed in master units.
Wall Lift Height Thickness of reinforced earth layers, expressed in master units.
Set Back Width Required distance for the face of the base of the wall from existing ground, expressed in master units.
Wall Width Factor Value used for mathematically determining the minimum width of the wall based on the wall height.
Additional Exc Width Optional distance for providing additional excavation area behind the reinforced earth wall, expressed in master units.
Min Reinforce Length If greater than zero, the width of the reinforced volume will either be "Wall Width Factor" x "Wall Height" or "Min Reinforce Length", whichever is greater. Expressed in master units.
Wall Excavation Slope Slope of the wall excavation on the back side of the wall, expressed in rise:run.
Embedment Depth Minimum depth below existing ground measured to the bottom of the MSE wall. This does NOT include the depth of the leveling pad. Expressed in master units.
BottomFootingProfName Name of the designed proposed base of wall profile. This is used in the second phase of the wall design.
WallChainName Name of the chain used for the face of wall stationing, (independent stationing from centerline).
UNLOCK Wall Foreslope Optional adhoc to allow the wall foreslope to "float" (vary) and always provide exact thickness for the top reinforcement layer.

FLH has two sets of criteria now available for use:

The .X30 criteria is the most recent set of scripts, so these instructions will be using the .X30s.

Retaining walls available with the .x30 criteria are shown below:

NOTE: click on each wall type below for an example of what the criteria draws:

This design concept consists of a multi-step process that involves not only the designer, but also the Structural and/or Geotechnical Engineer, with the final result being a set of proposed cross sections that reflects a constructible wall with a designed profile at the base of the wall and accurate earthwork volume calculations.

The "Steps" (explained in detail later):

  1. Create the initial proposed cross sections that reflect a retaining wall resulting from default values such as:


  2. From these proposed cross sections, use Geopak's Profile Grade Report and store a couple chains and profiles from "search text" (automatically drawn on the cross sections by the criteria) reflecting:


  3. Create an elevation view layout that reflects the 2 profiles. Provide this to the Structural and/or Geotechnical Engineer.


  4. From the elevation view, the Structural and/or Geotechnical Engineer will perform the actual FINAL wall layout, reflecting the stepped bottom of wall elevations.


  5. From the final layout, store the proposed bottom of wall profile into COGO reflecting the steps.


  6. Delete the initial proposed cross section elements, created in Step 1.


  7. Recreate the proposed cross sections using the stored wall profiles.

Step 1... Create the initial Proposed Cross Sections:

All of the retaining walls available to design using the criteria are driven by plan view elements. In some cases the actual horizontal offset position of this plan view element has no effect on the location of the wall in the cross sections, but simply acts as a trigger to tell the criteria to draw a wall against the edge of the pavement. The MSE wall is one of the walls that uses the exact plan view element's horizontal offset position as the distance from centerline to top face of the wall.

Note: For more information on how the other walls react to these plan view elements, see the documentation included in the "help files" available by clicking on the Description button from within the Project Manager run. A fragment of the dialog is shown below:

In our example here the edge of the pavement is 12.0 feet from centerline. Since the actual offset of the line matters in the case of this wall, draw the offset line at the exact offset for the top face of the wall. This wall will be located right of centerline from sta. 41+50 to sta. 46+50.

Invoke the Design and Computation Manager, I'll select Prop. MSE Wall and assure that Place Influence and Adhoc Attributes are toggled ON.

Adjust the Adhoc Attributes "default values" as desired, by double clicking in a field under the Value column, (as shown below):

Using Draw Transition, I'll draw a line 28 feet right from 41+50 to 46+50, as shown below.

Below is a screen capture illustrating the Prop. MSE Wall line, drawn 28 feet right of centerline:

Create the proposed cross sections as usual. Below is the result at station 44+00 illustrating the MSE Wall, drawn 28 feet right of centerline:

Step 2...Store the Chains and Profiles:

NOTE: You must have Geopak Road 2004 Edition version 08.05.02.55 or newer installed in order for the Profile Grade Report to work properly.

As mentioned earlier, in addition to drawing all the proposed cross section elements, the criteria also places "search text" at strategic locations that can be used by other Geopak applications... such as Profile Grade Report. If we look closer at the corners of the wall, we will see the "search text" as illustrated below from zooming in at each corner:

Top of Wall
(TW)
Front Bottom of Wall
(FBW)
            
Front Leveling Pad
(FLP)

NOTE: Two text nodes (FBW & FLP) are placed at the front bottom of wall. If the Leveling Pad Depth adhoc is set to zero, FBW and FLP will be placed on top of each other. In the illustration above, I have separated them for clarity.

We are going to use these pieces of search text to store Profiles and Chains into COGO using the Profile Grade Report.

The next step is to create an elevation view representing the initial (vertical) position of the bottom of the wall, resulting from the first cross section run.

It is important to note that at this point each cross section is independent from the other cross sections and have no relation to each other. In other words the result of the initial first run of cross sections does not produce a constructible wall design. The bottom of the wall will vary depending on the setback and embedment depth. In order for this wall to be constructible, the base wall profile should be flat or stepped in wall cell widths.

First let's store the chain and profiles that represent where the top and bottom of the wall would be positioned initially using the default adhoc values.

As you can see from above, it is possible to store all the chains and profiles at the same time. I would recommend setting the dialog to Sta. Text Alignment in order to reflect the true length of the chains/profiles.

Once the symbology for Existing Ground Line and Proposed Finish Grade are selected and Apply is pressed, the chains and profiles are stored into COGO as shown below:

NOTE: All chains and profiles will be stored with the stationing beginning at 0+000 (0+00 if your design is US Customary).

    

Step 3 ...Create the elevation view layout:

We can all agree that (in non-tangent wall sections) the actual length along the face of the top of the wall and the face of the bottom of the wall are different since the offsets from centerline are different. After lengthy discussions with our Structural Engineers, we decided that for simplicity, wall face stationing (top) should be used when designing the elevation view. Wall face stationing will provide a true length along the face of the wall.

Using the Draw Profiles tool, draw the Profiles previously stored into COGO. Create the Profile cell using the Top of Wall chain. Any other profiles will be "projected" to the Top of Wall profile cell.

The graphic below illustrates drawing the Profile cell using chain TOPW and drawing the COGO profile TOPW that represents the top face of the wall.

The graphic below illustrates "Projecting" the other profile to the Profile cell that was created from chain TOPW:

NOTE: Later, (in Phase 2) the criteria will be driven by a profile:

Give this drawing (above) to the Structural/Geotechnical engineer for final elevation layout. You may want to add grid lines to make it easier for them to layout the final wall design. We'll get back to this later.

Step 4 ...The Final wall layout:

Using the elevation view , the Structural/Geotechnical engineer would perform the following:

The Structural/Geotechnical engineer does not need to use MicroStation or Geopak to do this. This can be done on graph paper or whatever. You will then take these values and do the work in MicroStation/Geopak.

Let's imagine that after some thought the final layout has been done. You have been given the following by the Structural/Geotechnical engineer:

Step 5 ...Designing the final wall profile:

Once you have obtained the profile information from the Structural/Geotechnical engineer, use the Profile Generator to store the proposed profile into COGO. A fragment of the finished wall layout is shown below:

NOTE: The Profile that is used for the Proposed Bottom of MSE wall will define the Bottom of the Leveling Pad (if a leveling pad is desired). If the adhoc value for Leveling Pad Depth is set to zero, then this Proposed Bottom of MSE wall profile will define the bottom of the wall.

Step 6 ...Delete the initial proposed cross section elements:

Open your cross section file and delete all the proposed cross section elements (at least throughout the wall area).

Step 7 ...Recreate the proposed cross sections using the stored proposed wall profile:

Process the cross section run via Project Manager as usual. The results as shown below:

There you have it... a retaining wall in your cross sections that reflects the exact profile as designed. Since the wall is in the cross sections, you can now obtain staking notes and earthwork quantities that reflect the exact design.

Below is a fragment of the earthwork log file illustrating that the volumes for Roadway Excavation, MSE Wall Excavation and special Wall Backfill (shown below as Select and Granular) are calculated separately from the embankment and pavement layers:

As mentioned earlier, there are many other types of retaining walls that can be designed using our criteria in basically exactly the same manner.

Special NOTE:
Obviously, you will need many extra pattern lines in order to pick up the steps for the base of the wall. COGO's Layout Offset Chain tool will work perfectly for this.


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