Low Volume Road Design using Softree’s RoadEng ™

Overview

Start Designing

Auto-Balance

Horizontal Alignment

Mass Haul

Assign Templates

Pretzels

Design

 

Overview of Manual Method

Design with RoadEng is not much unlike the manual method. The only real difference is that the program does most of the number crunching for you. However, you still have to make the decisions on where the road is to go.

The following is just a quick review of basic manual design on paper.

You start out with the survey notes taken in the field, and from these, you plot out the plan and profile of the road, as well as cross sections for each survey point, each to a convenient scale. On the plan view, add in straight lines perpendicular to the P-line at each survey point for the cross sections.

Assuming that the road is grade controlled (as many low volume roads in the state are), start out the design by adding vertical tangents to the profile. Fit in a vertical curve for each VPI, then go along the length of the road and record the vertical offset of the tangent to the P-line for each survey point.

Now, for each cross section, record the corresponding vertical offset. At the appropriate height above or below the terrain, draw in a horizontal line. Then slide a template (can be easily made from an overhead transparency) left or right along the line to find the place where the cut and fill are balance. At this point, draw in a vertical line and record the horizontal offset.

For each straight cross section line on the plan view, put a mark for each horizontal offset. All the marks together represent the balanced road, but this result will probably not have very good horizontal alignment. At this point, horizontal tangents need to be added in along the offsets, but with the design goals in mind. Once these are drawn and the curves added in, the first phase of the design is done. Now just go through and update the offsets on the cross section sheets and on the profile. Aside from further tweaking, this is a rough design.

Enter RoadEng

Designing with RoadEng is not much different, just faster because you don’t have to draw everything by hand or measure scores of offsets. It has its own quirks, however, which shall be discussed later.

You should still bear in mind all the design criteria of the road, as this bears on what level of design is needed, and hence, how much it will cost.

One of the advantages of RoadEng is that you can quickly adjust the locations of PI’s and other design features.

When learning how to use RoadEng, it can be useful to have the help file open while designing.

 

Start Designing

Since most low volume roads are going to be grade-controlled, at least in western Washington and Oregon, it’s prudent to start with the profile. The first step is to add in the VPI’s.

To do this, just click on the profile at the points where you want a VPI. A tangent line will be drawn automatically to connect the points. Keep doing this along the whole profile. The tangents don’t have to be perfect the first time, just get them close. To move a point, right click the mouse. The cursor should change to a box, which you use to click on the design points and thus move them to wherever you want them.

Next, add in some preliminary vertical curves. To do this, click on the button with a "C" and a curved line in the menu. The cursor should now be a pencil with a curve instead of just a plain pencil. When you click on a VPI, a new window should pop up, where you type in the curve value. For vertical curves, the default is the Parabola K value, which is just the parabolic radius divided by 100.

Some time before or during this process, add in reporting points. These points don’t do anything for the alignment, but they do calculate an average cross section between survey points and can help to give a better estimate of earthwork. The easiest way to add them into the whole road is through the "Auto Generate" function in the edit menu. Select a fixed interval between 10 and 20 feet, and reporting for point type. This way, a reporting point will be added at the specified interval along the whole road.

 

Auto-Balance

Once these preliminary points are added, you can use the "Auto-Balance" option in the Edit menu. What options for self-balancing you choose depend on what view you start with. Since in this case you start with the profile, then choose the horizontal alignment. This holds the vertical alignment and curves constant, while moving the horizontal alignment at each selected point to produce a balanced alignment. Read through the help file on this to get a good idea of what is going on.

RoadEng does state that there are some problems with the horizontal alignment option and that it may have to be run twice in order to get the results close.

Another thing to note on the self-balancing is that it does not produce exactly balanced cross section. As well, the resulting horizontal or vertical alignment from the balancing does not generally produce a good design. However, it does give a good idea of the relationship between the plan and profile, how moving a point in one affects the other. So, take a look at the horizontal alignment and consider it a starting place. Step through all the points while looking at the plan and section windows and figure out where the horizontal alignment should be to provide a good road.

Another Way

There is another way that the sections can be balanced. It takes a little more work, but may provide for better results. The first step is to use the auto generate function to remove all existing reporting points, and at the same time to add new reporting points to each survey station. Once this has been done, deselect the vertical alignment option in the section options window. Now, with the section window active, start at the first point and manually move the road left or right until the cut and fill are about equal. Hopefully the cut and fill area details are in the bottom of the section window. If not, turn them on. Preferably, the cut should be slightly higher than the fill. Keep going from point to point using the arrow buttons and repeat the process. It will take longer, but the results may be more accurate than the automatic version.

Horizontal Alignment

So the road is balanced based on the profile. It is time to go through the plan view and work up some horizontal tangents. Since the alignment is bound to be a little too crooked for trucks to drive, you’ll have to start making some compromises. "Do I cut more here, or fill more there?" "If I push the alignment into the bank, I’ll be cutting more, to avoid that, need to slack the grade." This is where the design gets fun, since you have to really visualize what the road does when you move the alignment around and how to correct for it in the other alignment.

Get the horizontal tangents in and put in some preliminary curves. Then start going back and forth between the horizontal and vertical alignment to get close to a design. Keep in mind that certain additions will need to be added, such as turnouts, curve and fill widening where appropriate, etc.

 

Mass Haul

Another thing to keep in mind is the mass haul. When designing, keep an eye out for where the mass haul is rapidly gaining or losing material. In places where it’s gaining quickly, find a way to eliminate some of the earth, unless you’re doing a full bench design, at which point endhauling to a designated waste site will probably be necessary.

Ideally, you will probably want to allow a slight gain of material along the road, somewhere between 15-25 cubic yards per station. It may be more or less depending on the site, so look at the constructed roads nearby to see what sort of material came out during excavation. Allowing a gain of material simply accounts for unexpected holes encountered during excavation due to hidden boulders, stump holes, etc. In any case, it’s usually better to have a little extra material rather than not enough material.

 

Assign Templates

At appropriate places, the road will need turnouts, usually every thousand feet or so. For curves with a radius of one hundred feet or less, curve widening will be needed. Fills at the shoulder greater than about two feet need slough widening to account for sloughing. Widening values should be appropriate for the road, the design and critical vehicle, use level, etc.

You should have a template made up for each of these cases, which will be available for assignment to specific portions of the road from within the "Assign Templates" option in the edit menu. Basically you should know where the start and endpoint of each template should be. The input should also be in P-stations, not L-stations because the design stations move around, whereas the survey stationing is constant. At the same time, when printing out design summaries, the final locations of templates and other design elements should be in L-stations.

 

Pretzels

It is possible with RoadEng to get some really messed up alignment for apparently no reason at all. In this state, the road sort of resembles a pretzel. The common way for this condition to occur is when working with acute tangents, especially on switchbacks that have been poorly surveyed.

The first way to avoid pretzel roads is to ensure that the road is surveyed in well the first time. When working with tight curves and switchbacks, it pays off to take the extra time to do a little field design with a curve deflection table before surveying. This way the design is a little closer to what is laid out on site.

The next way to avoid pretzels is to not form acute angle with horizontal tangents. They just don’t work, so make the maximum angle between tangents 90 degrees.

 

Odds and Ends

One of the last things to note is an oddity of RoadEng where the profile topo line will get little pits or spikes in it. These don’t generally seem to do much harm, and why they appear is strange. It seems to have something to do with reporting points, but they can be both the cause and solution to the problem. Sometimes taking the reporting points fixes it, sometimes it makes it worse. Just treat each individual case as it occurs.

 

Tuesday January 15, 2002