The Art of Grading 5

[UrbanDesignr]

It seems that site grading is one of those things they never teach you in school, but expect you to know on the job. I have had some exposure to grading in the past and have been able to work my way through it, but never felt that I had a firm grasp on the procedure. A big grading job was just presented to me and I want to take the correct approach to it.

Can anyone recommend a book or (better yet) an online resource that lays out the proper steps to take when approaching a grading design? Or can you offer me tips on what the steps are? Where do I begin? I am specifically interested in grading for residential and commercial site development.

 

[cvg]

coming from a drainage background, I see too many designers laying out their sites and then giving the plans to the drainage engineer and ask him to "check the drainage". Planning the drainage first is essential to reduce wasted time on re-designing site grading.

Secondly, get the geotech to give recommendations before starting the earthwork.

 

[DarthSoilsGuy]

Land Development Handbook published by McGraw Hill
is a standard read for civil firm and you won't regret owning it.

2nd the motion that you should be learning drainage at the same time. Drainage drives the grading at my office on most of our projects.

different CE firms have their own style for everything so you shouldn't be expected to pick it up and run with it the whole way. Read the chapters on the stuff you don't feel comfortable with and work on it from there.

Also, grading is more or less a culmination or compromise of dealing with all the issues on the project. (Road, parking, sidewalk, utilities, drainage design, wetlands, and a whole bunch of other permitting and site constraints specific to the job)

 

[civilperson]

Site grading for sub-divisions:
1) Follow the natural contours wherever possible
a)Put the drainage conveyance along the natural stream bed alignment and also put the main roadway/sanitary sewer parallel and close.
b)Try to not cross into another drainage basin with runoff or sewage.
c) set the road center line about 2.5' lower than adjacent building pads, (ranch style), or 4.0' lower if basements are standard.
d) Drain each lot to the public ROW,(not onto a neighboring lot).

2) DIRT IS CHEAP, no retaining walls or abrupt change in grade. Minimum slope is 0.8%, maximum is 7-8%. Use 25-50' tangent slopes out of intersections, pick up gutter flow upstream of intersections.

3) Follow all zoning rules and setback requirements in the initial layout. Side yard, front yard, back yard set backs and % green space.

 

[BelspringKen]

I want to re-iterate (3) from civilperson - read those local codes. You may find in some areas that you can go slightly flatter - I have seen 0.5% pass as a bare minimum on a longitudinal grade, and 10% as a max in a mountainous area. Talk to the plan reviewers if you need to do that, to make sure you and the reviewer are on the same page.

So read those local zoning codes and regs... pay special attention to the SWM regs for quantity and water quality.

 

[UrbanDesignr]

Thanks for the advice all!

Id get into the site details but its a can of worms. I may post later if I have specific questions. I think I'm getting the hang of it. Your tips have been helpful.

 

[queque]

This is excellent advice from everyone. We always start by calculating existing inflows and existing outflows. Next, revised outflow caclculations based on extent of development.
Then the drainage plan is coordinated with the developer's ideas about layout and related grading . Location and sizing of detention basins is part of pre-design.

 

[UrbanDesignr]

As it turns out, we are holding off on the grading until we get the drainage worked out. This is the approach you all have suggested and I think it is the best way to go. The developer has the site overdeveloped and left no room for stormwater detention. We are required to hold 5" across the site, so siting the numerous dry wells is turning out to be a nightmare. In the end, development may need to be scaled back, so grading at this point would be foolish, as the plan may change drastically.

 

[civilperson]

Try oversizing the stormwater conveyances to increase the volume on site and restrict off-site flow with orifice or weir. A creek bed with trails/greenspace alongside can hold large quantities of water for 12-24 hrs after the storm event with minimal damage to the facilities.

 

[BelspringKen]

No room left for detention pond? You may be doing an underground system, under a parking lot. Vendors may be able to help in the sizing of the system.

 

[UrbanDesignr]

Thanks for the last 2 suggestions.

When I say the site is maxed out, I'm not exaggerating. Its urban infill so there is no room for an open drainage pond and all of the parking is buried, so an underground system also is unfeasible. We have some room in the driveway, so that may be an option. One of the rare cases where a parking lot would actually be desirable.

 

[cvg]

if the site is small, underground can still be feasible. I have seen it used in the basement level of a parking garage before. Main concern with this design is disposal of the water. Make sure your dry well can handle it, or provide a small pump to discharge the water once the basin is full.

 

[sammyk]

Drainage and Grading go hand-in-hand.
I love the title of this thread because grading/earthwork/drainage is an art that is best learned from someone thats already good at it.

On residential subs. your roadways profiles dictate everything. So getting the profiles right are critical. Overland flood routes (and drainage in general) have to be considered when setting these profiles including the amounts of excavation coming from your basin digs (which dictates how much below or above existing grades you need to set the profile at).

The reason this is the most important topic in land development is that Earthwork is the one area of development where you can save your client lots of money if you do it right. A balanced site means no haul-off or double handling of material. Not to mention that if you get it wrong, drainage problems will leave you open to serious liability.

 

[sam74]

I'll give you a star for that sammyk.

Some people just don't get it. At my last job some mid-management decided we were going to standard sheets which would involve separate grading plan sheets and separate drainage plan sheets. Made no sense at all. From the design standpoint or the contractors standpoint.

Oh well, I just do the work. Right now anyway. It is good to have faith in your managements decisions, maybe that is part of the reason why that is my previous job now.

 

[sammyk]

Sam 74,
Heres the biggest problem in the engineering community:
By the time you get good at something you are pushed to mid-management and no longer do serious ground level engineering, you become a project manager. That leaves the newer kids to do these critical drainage/earthwork routines.

This topic should never be given to the younger engineers without extreme oversight. Sometimes the mid-management role leaves insufficient time to train the young ones in this extremely important topic. I wish it was different.

 

[UrbanDesignr]

I agree completely Sammy. Furthermore, given the nature of the consulting business, few firms actually take the time to properly train their young engineers because it is not billable. However, the time spent in properly training engineers would surely be saved in improving efficiency (less mistake, less having to redo things 3 and 4 times to get it right.

Also, I've always felt that this should be covered in school. 4 years of advanced calculus does little to teach site grading or utility coordination. A colleague from Australia took a 2 year 'college' degree where he learned some of the more practical aspects (survey, grading, how to lay out a road) then went on to 'university' to learn the theory. Seems like a good way to go IMO.