Sloped Excavation Surfaces

Terminal Excavation Elevation (TEE) is going to be used to refer to the target final elevation to be reached during excavation in a set location. This post is applicable to projects that work on a grid (like a chess board) and will excavate each grid down to an assigned elevation. This process creates an excavation surface with a consistent slope for each grid. We will be creating "levels" of TEEs. The first level will have local maximum TEEs. We will then hide that level and repeat the process. We will be grading the TEE levels in order of creation. This process cuts the higher TEE sloping where we will actually be digging deeper, thus creating a pretty accurate model of what the excavation surface will look like upon completion.

Step 1: Create TEEs

Create an excavation boundary (to be modified later):

• With sheet pile constriction
• Without anticipated sloping extension

Keep excavation boundary frozen until finished with excavation surface.

Grade the grids as full grids. We will trim the excavation surface later with the excavation boundary.
Create the TEEs as 2D Polylines so that they will have the same elevation on all vertices.

• Layer: _###-C-EXCAV

One way to create the TEEs is to draw a 2D polylines just inside the limits of the grid. You want to leave about a foot between TEEs.

Another way to create TEEs, especially if you have a lot of them, is to create a csv (PENZD) file with a point number (P) center of grid coordinates (E and N), TEE (Z) and Grid ID (D). You will create a point group that you will use to format COGO points into 2D polylines at the correct elevations. This point group has no description and has square around the point with the desired side length. I will import your csv file to your point group and then isolate them in the drawing. Select all of the points and explode them multiple times until they are no longer COGO points, or blocks, but polylines.

QC that they have the right elevations.

Step 2: Create Target Surface

 This surface will be used during the grading process. We will be grading the first layer up to the pre-construction surface. We will paste the first level into the target surface and then grade the second level to that surface. We will paste the second level into that surface and grade the third level to that surface, etc...

Paste in the pre-construction (existing ground) surface to a new surface called "0-Target".  

Step 3: Levels

We will be creating feature lines for the polylines we created to do they actual grading, but we will be saving the polylines as references. A benefit of preserving your TEEs as polylines on separate layers, even after you finish creating your excavation surface, is if you have to go back and recreate the surface for some reason you will already have the TEEs separated out onto different layers. It saves you from having to recreate TEEs if you need to alter something.

Create layers for your levels:

• _###-C-EXCAV-1
• _###-C-EXCAV-2
• _###-C-EXCAV-3
• _###-C-EXCAV-4
• ....

Create a layer for your feature lines:

• _###-C-EXCAV-FL

This layer will be used to isolate your feature lines so that they can be deleted after you have graded them (level by level).
Locate the local maximum TEEs.
Put them on your first level layer.
Double check that they are 2D polylines and have the correct elevations.
Create feature lines from your first level.
Uncheck the box that says “erase existing entities.”
Put the feature lines on your feature line layer.
Freeze the first level layer with your polylines.

Grade the temporary feature lines for your level:
Create a group for your feature lines:

• EXCAV

Set your target layer:

• 0-TARGET

Set your grading settings:

• Grade to Surface (Cut Up Only)

Start Grading:

• Select a feature line.
• Click outside of feature line.
• Yes to apply all around feature line.
• Hit S to assign your slope
• 1.5H:1V or 1H:1V
• Grade all feature lines on the level
• DON’T FORGET TO INFILL!

Create a Detached Surface:

• EXCAV – 1

Object View to QC the new detached surface.

PASTE THE NEW DETACHED SURFACE INTO THE TARGET SURFACE!

Put your surface to no display.
Clean Up Your Grading.

Quick Select all of the feature lines and grading and delete them. This should get rid of all of your grading, including the features lines, which is necessary to accurately grade your next level.

QC the Target Surface:

• Turn on the target surface.
• Object View to QC.
• Put target surface to no display

Repeat for Next Levels:

• _###-C-EXCAV-2
• _###-C-EXCAV-3
• …

Do this until all of the TEEs are graded.

Step 4: Create Excavation Surface 

Create a new surface called "EXCAVATION."
Paste Layers into new surface in order of creation.
Object view to QC.
Turn on excavation boundary.
Adjust the excavation boundary based on where sloping is allowed to occur (absence of sheet pile).
Add boundary as an outer boundary to surface.
Delete and swap lines in the surface where necessary.