Initially, the biggest impact from machine control came to the heavy highway contractors. I can remember when Blade Pro 3D and a robot could make crisp crown transitions and get contractors bonus money for smoothness. Even with machine control technology being used in all aspects of civil construction, highway work still benefits from being on the front lines of development. Construction technology manufacturers know the high stakes associated with this work and focus their development on being first to market for new concepts and improvements.
Over the years we have made sure to be in front of the curve. It is satisfying to help a contractor by providing the correct files for their new technology. A client that is new to high level machine control may not initially want to be tasked with model building in addition to field responsibilities. Equipment manufacturers put data modelers together with these people to make things easier. This only happens because the manufacturers trust our work, guaranteeing success. I will cover some things we have been doing for years as well as some newer uses for data in a road model.
International Roughness Index (IRI)
IRI is the standard to quantify road surface roughness. A continuous profile along the road is measured and analyzed to summarize qualities of pavement surface deviations that impact vehicle suspension movement. Reported in units of inches-per-mile, the IRI describes how much total vertical movement a standard passenger vehicle’s body would experience if driven over a 1-mile segment of the subject pavement at 50 mph. IRI is useful for assessing overall pavement ride quality; a higher IRI value indicates a rougher road surface. A good IRI is less than 95 inches per mile while poor is over 170.
Various methods are used to measure the index, from simpler manual units to electronic systems. Contractors will receive a bonus if the IRI is within tolerances specified in the contract documents. Different types of roads have different requirements depending on location, number of lanes and traffic count.
The reason I mention this is that as competent model builders we can improve the contractor’s chance of getting their IRI bonus. When value engineering is allowed, or the job is a design/build, we can adjust the profiles and super elevated curve sections to make machine control better. We are talking about precise adjustments in parameters to improve the surface. All roads need to be in specified tolerances. When there is some latitude allowed, we can make things better.
The way a model is built plays a big part in making a road turn out smooth. Using an older program like Terramodel and then converting that into an xml surface will cause problems that will never be worked out in the machine control’s attempts to get things right.
To create a model that can be properly read by machine control starts with a road job, meaning alignments and templates. Native software can easily make sense of these elements and go a long way in producing great roads when using the same brand of machine control as the software.
Paving Only Models
We have a lot of clients that are performing paving only, weather asphalt or white paving. They are going to be paid for a specified thickness of material over the base. The easiest thing for them to do is trim the base with an elevation dial down. This allows final checks of the lower priced base then the finish will be parallel to the stone.
When another contractor is doing the subbase, things can get complicated.
- Do they use machine control, is it the same brand?
- They may rely on stringline.
- What tolerance are they held to for base? (This can cause issues with minimum depth requirements.)
In these situations, we work hard to get everybody on the same page. Yes, it can get as difficult as it sounds. We stay on top of things and eventually help the job to get on track. The last thing anybody needs is finger pointing when the job is not correct.
When performing paving we need to add a place outside the paved area for the machine to smoothly follow the road profile. This track grade needs to be included as a separate model to subgrade elevation.
An average horizontal distance is 5-feet. When building this, we must be careful with stepped subgrades and super elevation transitions. These complicate things and call for special procedures. The result must be a smooth extension of the roadbed, so the paver does not jump or make exaggerated corrections.
When paving is done, the work needs to be covered up and normal shoulder and grading slopes will need to be made. This requires a different model to show how things will look when finished. Any road job starts with templates that represent the finished work. When we get things to final condition, we can now do dial-downs for subgrades, edges, and slopes. Multiple models make things more difficult for the field. Make sure everybody is on the same page. The best way to accomplish this is to have one person in charge of loading machines and rovers.
As I mentioned, we start with a complete model from catch to catch. This means we are intercepting the existing ground with the correct slopes and transitions. A different model will eventually go to the paving sub, but when we start with a complete model there is no doubt how the individual pieces will fit.
- The most critical component are the driving lanes. Make sure all elements are correct and correspond to the plans. We see differences in COGO math with alignments all the time. It is up to the model builder to get things correct, even if the math seems a bit off. This could be an entire post on its own.
- On roads with curbs, attention needs to be made to the base under the curb. Many plans are drawn with intricate steps and slope changes. You may find out later that “we just do it this way” simplifies the job. Check with the stake holders to confirm. We might make an intricate model that has to be redone and simplified based on local value engineering.
- Side slopes are typically easy. You may find special fill materials being used for improving erosion resistance. Be careful of your trigonometry when calculating the actual depth of the material. This stuff is usually expensive, and you do not want to waste it.
Slope Stake Reports
Whether it is for the field to use, or a requirement of the job, slope stakes can be a big help when used properly. The biggest advantage is the ability to use non-guided machinery to do most of the heavy lifting. When things get close, machine control can get it right on the money. Producing these reports is not difficult when using the software used to make the initial model. This is another reason we start with a complete daylight model. Slope stake reports are just a few mouse clicks.
For reporting options, we always default to what the contractor and surveyor on the job are used to. Remember, it is easy to customize reporting in the office and difficult to try and rethink an unfamiliar format in the field.