One of Mark's recent students and a current InRoads intern asked for Mark's help on a grading and paving project she is working on:

Hello Mark,

I don't know if you remember me from the class this spring but I have a question about a repaving project that I am working on. I have an existing ground surface DTM that includes ground shots, curbs, flowlines, building outlines, etc. and I know that all of the asphalt in the facility is being demolished and repaved and so I am wondering what you think would be the best way of creating a proposed surface from which I could generate proposed contours? So far in InRoads I have been involved in setting up the XIN, creating profiles, and putting together existing ground surfaces and that has been a lot of fun, but I know there are many more tools available to me that I have yet to learn so I am hoping you can nudge me in the right direction.

Obviously I need to keep the features that will not be demolished or changed like curbs, buildings and concrete but where I get stuck is trying to figure out how to use InRoads to design the asphalt to adhere to minimum slopes that still match the features that will remain.  

So far I have come up with the idea of generating existing contours to start, then modifying them and importing them as design. But I am wondering if there is any tool you would recommend that could create slopes in the ground surface but still match existing features? I have attached a PDF of the existing ground and I would appreciate any feedback if you get a chance!

Thank you for your time,

Alejandra 

Here is the Zen Dude's response:

Hi Alejandra!

Of course I remember you!! 

Regarding your question ... oh boy. There is no easy answer. InRoads has always been seen and used for roadway design, but site design has always been an 'art' with InRoads. Interestingly, most of my experience is with site design ...and not roadway design so I'm unusual in that sense (and other senses as well)  : P

I don't even know where to start without spending an hour writing something up. One thing I will say, is the contour route isn't the way I would personally go. The only time I use contours is for landscaping, golf courses, and other 'soft' grading. You are correct regarding using all the existing features that you can as parts of your ultimate design.

Your main tool palette is the Surface Design tools and Surface Editing tools. These act like a toolbox and you have to know most all of them so you can pull out the right tool for the right task. 

When I teach a site design class I basically go through every single tool in both of these sections and explain what they do. The tricky part is that you can obtain similar results using different tools and different techniques. I know I'm not being too helpful, but this is a tricky thing to explain. I've been wanting to take the time to write up a site design book but just never carved out the window ... plus, it's not just about knowing the tools. It's fundamentally about understanding grading and site design. ...remember, these are just "tools". It's the calculator ...they aren't the engineer. A while back I started to write my site design book and realized that it would have to discuss the "how" site design is done within the descriptions of the tools.

One bit of guidance that I give you is ... forget about the tools for a moment and focus on where your key grades (highs, lows, and catch basins) and grade breaks are. Where you want or need straight grades to occur like along a flow line. Then it's just a matter of picking the tool out that will place that information in the DTM. Once the key grades and grade breaks are in the surface the triangulation will form the 'planes' between the 3D elevations that you've defined. But ... I would try my best to stay away from drawing contours ... unless you absolutely have to. That's a trap that can unknowingly introduce potential conflicts if you're not careful. That's probably the biggest 'philosophical' difference between doing site design with InRoads versus the 'old school' ways. Some guys just want to sketch out contours. But it's a sloppy imprecise route in my opinion. Layout your key control and then check to see if the resulting contour display matches your grading concept.

Civilly yours,

- zen

   

Hello :-)

  

Right after I emailed you I realized the contour way would be a mistake since I would be very much restricting the model from any design changes. So then I came up with this approach: focus on an area at a time, take the existing feature that will remain and parallel copy it radially inward to an elevation where the design minimum slope occurs and do this until the design slope conflicts with the nearest existing feature. For example, I don't allow the elevations of my control features sloping from the gutter be greater than the building they are approaching. In my mind the focus behind this is the existing features that I want to grade between as smoothly as possible so this allows for every point along a gutter, for example, to be met by the same slope... but now I am wondering if I am still just doing the same thing (creating contours) or if I am focused too much on the existing features? I will create another surface today, focusing on grade breaks and control information I can define.

 

I greatly appreciate your time,

 

Alejandra

                                           

Hi Alejandra!

 

You're approach related to focusing on the existing features and developing the design elements from those is correct. Do this wherever you can. You won't be able to do this everywhere, but it will get you started. There are three aspects to site grading like this:

 

1)      Areas that tie into existing - in these cases you will actually use the existing features from the existing surface and bring those into the new design DTM. You may also create 'new' features based on the existing DTM by doing things like drawing in a 'saw-cut' line in MicroStation (or using InRoads tools) and then draping it onto the existing surface to extract the grades.

 

2)      Areas of the design that are relative to existing features - in these cases you will use the Design or Editing tools of InRoads to develop design features that are based on existing features like taking an existing parking lot pavement edge and projecting a 2% grade from that edge using the Generate Longitudinal Feature command.

 

3)      Areas of the design that are completely independent of the existing - these are truly 'design' elements like the establishment of a catch basin location or a high or other low spot.

 

 

I hope this helps!!                      

 

Civilly yours,                                                      

- zen