Grading steps for a surface with simple retaining wall made of CMU

[qureshikhizar]

Hello,

I need help with steps to grade this surface when we put a retaining wall (red)

red= wall

yellow=conc pad

Green=feature line but im not sure if we can use feature line grading here

blue=existing building

cyan=tower, goal is to put telco equipment on the yellow concrete pad and a cable bridge will carry cables uphill to tower

Issue is that the grade is steep where we need to put the pad (10x15). need 2-3' around the pad as well as you can see. 

I THINK YHERE ARE 2 APPROACHES TO THIS,

1=Grade and prepare the surface and just show the retaining wall as i have shown in plan and

2= Use civil 3d sub assemblies to put retaining wall and probably civil 3d will generate proposed contours and profile view if required.

Please guide me how to do this.

Thanks

[rl_jackson]

Just my take here, I like to keep things simple when I can and I'm sure there's multiple solutions to this.

1. red line: Wall you need an idea of what the yellow line is going to be? Is there a slope from yellow to red and is blue ultimately higher than yellow? With the idea of yellow I'd draw a featureline (FL) at an elevation that was less than yellow as a wall generally has one elevation, offset the FL a small amount .05, then this resulting FL would take on the elevation of the surface (i.e. creating the wall face), the other red lines would create the top of the wall.

2. Yellow, needs a little slope for drainage not a hill, but it's all probably based on the blue building...

Just my take at creating a simple FG (finish ground) surface, no grading objects or anything hard.

A featureline is a surface, if you want to make it one, using the tools at hand makes for an easy life.

NOTE: In this process I've created a new surface prior to starting with #1 and all the new stuff gets added to that surface.

[gherrmanRQ549]

You probably don't need to make a TIN surface for the wall itself. I'll do that sometimes when the geometry is complex and I want to use Civil 3D to calculate materials volumes (cy of concrete). But here, adding that information to your model doesn't really gain you that much. What you should consider is how you're going to backfill the wall. Are you going to backfill right up to the top and let any stormwater flow over the top of the wall? Or you going to slope the backfill from SW to NE (in which case do a spot elevation for the backfill at each corner)? In either case, you have the option of creating a TIN surface for the backfill and showing the FG contours there if desired. Or a couple of spot elevations and a text note specifying the grading would work too.

[Neilw_05]

You might consider using a corridor with a Featureline as a baseline. Define a featureline to represent the bottom of the slope and add as a baseline to a corridor. Then define an assembly that uses a Daylight Bench subassembly. This will create a slope with benches according to your parameters until it catches existing grade.

[gherrmanRQ549]

@Neilw_05, I had the same thought, but in order of complexity, I'd rank the options from easiest to most complex as:

• No retaining wall TIN surface
• Retaining wall TIN surface with standard breaklines (top and bottom breaklines offset by some negligible distance like 0.01')
• Retaining wall TIN surface with wall breaklines
  • Backfill surface can optionally be generated in any of the above configurations by setting backfill elevations on a 3D polyline or feature line and grading at desired slope/grade back to existing ground.
• Retaining wall TIN surface generated from corridor.
  • Backfill surface can optionally be generated from the corridor with appropriate subassembly or via the method outlined previously.

[Neilw_05]

When it comes to modeling walls, You don't need to model the wall with the TIN. All you need is the FG dirt at the top back and bottom face of the wall. The wall itself should be modeled by a structural engineer using Autocad structural tools. So using the benched daylight subassembly you can account for the wall thickness in the batter parameters. This should get you close.

If you want to be more precise,  use offset alignments or featurelines for the walls. There is no Easy button for this.

[santhoulakis]

Does it really matter to show elevations on top of the wall?

If no, you can just have a feat. line for the whole wall. It will just have ground elevations just adjacent to the wall.

If yes, you can add one more feat. line, inside the first one and offset by a small distance. It will have the top of the wall elevations.

[Neilw_05]

Top of wall will not be a linear progressive transition elevation. In most cases it will be stepped at some interval to fit the finished grade based on the type of materials used to build the wall. If it is a CMU block wall (US), the steps will be at 4"x8", 8"x8" and 8"x16" increments. Civil plans typically don't provide the details for where and how the wall and footing is stepped. Thus modeling the exact top and bottom of the wall is meaningless in the civil plans. The structural engineer needs the finished grades at the top back and bottom face of the wall to calc the actual top and bottom of wall elevations. That is what needs to be provided in the civil plans.

[santhoulakis]

Assigning some assumed but realistic elevation to the top of wall could
just provide a more realistic view - probably unnecessary most of the
times. I wouldn't show those elevations on the plan cause as you mentioned
it is the structural engineer's job.

[Neilw_05]

All you need to care about is the dirt. Make it do what you need it to do and let the structural guys figure out their part. 

[gherrmanRQ549]

Unless you're also the structural and you just feel like doing it 😉 If it's a cast-in-place concrete wall with no or few transitions, that's fairly straightforward to do with breaklines. Start adding in lots of transitions - as in a CMU wall - and your best bet is to use a corridor with a profile(s) (as needed: top of wall, top of footing, bottom of footing) or just abandon the idea of modeling the wall with a TIN surface.

[Neilw_05]

If it is your job to provide the exact details for the wall, then you will need to provide an alignment for the face or back of wall, providing the finished grade dirt elevations at the back and face of wall. Then you will lay out the top and bottom of block in the profile view to fit the finished dirt grade, stepping the wall based on the material used (block vs. poured concrete). This is a very detailed approach to presenting walls in a civil plan.

Keep in mind, C3D cannot model absolute vertical steps. Thus any steps in your wall profile will have to have a slight horizontal offset to be functional in C3D and thus will NOT represent the true locations..

[gherrmanRQ549]

But getting back to the civil considerations at hand.

1) I wouldn't site the project so close to the existing building. You're creating access/maintenance issues for the occupants.

2) As @rl_jackson said, slope your concrete pad towards the opening in your retaining wall.

3) Once your wall is sited, you can get an initial max height of unbalanced backfill to give to your structural so they can start designing the wall. They'll take care of designing a footing and reinforcement schedule, but you do owe them how tall the wall needs to be.

4) I'd look at eliminating the NE section of the wall.

5) Any existing drainage structures near the existing building?