Help with Subassembly Composer - Creating a Multi-Layer Breakwater/Dike Assembly

[Kamiriyoucef]

Hello everyone,

I am currently working on a dike reinforcement project in Civil 3D, and I'm struggling to create the custom Assembly using Subassembly Composer (SAC).

1. Project Goal: My objective is to build a parametric assembly that models the reinforcement structure shown in the attached cross-section. The main layers to be modeled are:

• A primary armor layer of BCR 40T concrete blocks.

• An underlayer of ENR (3-6T) rockfill.

• A toe berm structure with a BCR 17T armor layer over an ENR (1-3T) underlayer.

• A concrete crown wall at the top (elevation +8.50m).

Here is the exact cross-section I am trying to achieve: (Remember to insert your image here. It is the most important part of your post!)

2. Where I'm Stuck: I'm having a hard time figuring out the correct logic and workflow in Subassembly Composer to build this complex geometry. My main questions are:

• Layering Sequence: How can I correctly create the different layers (BCR 40T, ENR 3-6T) which appear to have a constant thickness perpendicular to a complex, stepped slope?

• Creating the Toe Berm: What is the best approach to model the toe berm structure (with the BCR 17T and ENR 1-3T layers) which is located at a specific elevation (-9.40m)?

• Handling the Stepped Geometry: How should I manage the multiple slope changes and benches (the "steps") in the ENR (1-3T) layer? Should I use a long sequence of Points/Links with X/Y increments, or is there a more efficient, "smarter" method?

• Targeting the Seabed: The base of the structure at -13.40m (marked "Var." on the drawing) needs to follow a variable DTM/Surface representing the seabed. How do I properly integrate a Surface Target for the foundation of the toe berm?

3. What I'm Looking For: I would be very grateful for any guidance on the general methodology in SAC for this kind of structure:

• Where is the best place to start building the assembly from? The top of the crown wall? The tie-in point to the existing ground?

• What sequence of tools (Points, Links, Auxiliary Points, Decisions) is most suitable for this type of stepped profile?

• Any tips for making the layer thicknesses and bench elevations parametric so they can be easily controlled in Civil 3D.

Technical Information:

• Software Version: Autodesk Civil 3D 2026

I have attached the detailed cross-section drawing to this post. I am happy to provide any further details if needed.

Thank you in advance for your time and valuable assistance.

Best regards,

[nkiakas]

Hi @Kamiriyoucef 

Is zero reference layer the blue NGA and all levels like -5.75 of BCR-40T refer to this zero value? What is the NGA? The natural ground?

What is the surface down right where the slope 3/2 of BCR17 daylighting?

Do you want to build the subassemly from your green line and above or everything in the picture including BLOC ARTIFICIEL,BCR 10t and ENR 15-45t a,d 0.5-15t?

Regards

[ecfernandez]

Hi guys! @nkiakas question is key. What would be the proposed geometry? that is not very clear to me.

I would add: set what the origin point would be for your subassembly and start creating it based on elevation and surface targets. My suggestion for the origin point would be this (I might be wrong as I did not fully understand what the proposed geometry would be):

If you like this, I would suggest to get started with the custom subassembly. If you have more questions when proposing the subassembly geometry, you can post them here, and we'll be happy to help.

Best regards,

[Kamiriyoucef]

Hi @nkiakas,

The NGA corresponds to the sea level reference, meaning elevation 0.

Yes, I want to build everything above the green line, including the artificial blocks, BCR 17t BCR 40T and ENR 3-6t, 1-3t.

[nkiakas]

Hi @Kamiriyoucef 

Is the blue (NGA) constant absolute elevation? (for example 0m? or +-0.25 depends from tide, sea level is not always 0) or its represented by a surface, or a 3d polyline?

What is the width/height/slope of the BLOC ARTIFICIEL steps?

Is the bottom of the sea represented by a surface?

Regards

[Kamiriyoucef]

• Yes, the blue (NGA) is constant and corresponds to the elevation 0.00 m.

• The width, height, and slope of the artificial blocks are as defined in the DWG file.

• Yes, the seabed is represented,  as a natural terrain surface.