InTrans / Sep 29, 2014
What makes a road last longer?
posted on September 29, 2014
When you are driving on a highway, do you ever imagine what the land was like before the road was constructed? For instance, do you consider the difficulty in building a road into a mountain side or over a hill? Many transportation workers—like construction managers, geotechnical engineers, and traffic designers:consider this question carefully. Building a sound foundation for pavement is very important to ensure long-lasting roadways. This ground work is called Earthwork, which is considered to be one of the most important parts of roadway construction.
Why is it important to have a strong foundation?
Let’s look at one important step of the Earthwork process so that you can see for yourself: compaction.
First, the land intended for a roadway must be cleared and compacted. If the soil is too dry during compaction, a rain event can cause an unexpected settlement to occur and change the foundation. If, for example, the soil is too wet during road construction, then the heavy equipment can actually impede the construction process. As you can imagine, the timing for this process can be very difficult! Factors like water drainage, weather, and traffic frequency are very important in considering the design of the road. If the compaction is done incorrectly, the road is much less durable and will have a shorter life span. When you consider a generic two-lane rural road can cost over $1.7 million per mile, the initial groundwork becomes a very important piece!
Iowa State University’s Center for Earthworks Engineering Research (CEER) has been studying intelligent compaction. The goal is to construct pavements that last longer and maintain high satisfaction from the public. Since road maintenance costs are very high, the less maintenance means more savings in the long term.
A conversation with the Assistant Director for CEER, Dr. Pavana Vennapusa
Compaction seems like a pretty easy part of road construction to an unfamiliar person. In reality, though, there is a lot to compacting soil. Can you describe some of the important steps?
Compaction plays an important role in how roads, embankments, dams, and levees perform. Some of the most important elements of compaction include the type of equipment used, and measures followed in the field such as how thick of a lift is placed to compact, how much moisture the soil has and how many passes you make. To compact soil adequately, you need the right amount of moisture content and you need to use the right type of equipment for a given soil.
To assess and properly compact the soil for use, you need experienced engineers in the field. Currently, we are facing a shortage of experienced engineers. Excitingly, new equipment technology has drastically changed how we assess compaction, reducing the need for experienced engineers on site at all times. New technology includes equipment that provides real-time color-coded graphs, to a roller operator showing how well soil is compacted. This alleviates some of the pressure to get experienced construction workers on every construction site.
Do you think that due to some soils, there should not be roads in certain places; do some roads (specifically in the US) create more maintenance issues by locating where they are?
Absolutely. There is an engineering process to classify suitable soils for roads, but ultimately, the performance of a road relies on where it is located and how they are used or modified during construction. For example, roads in Texas must be designed to withstand hot summers and wet monsoons, while roads in Iowa have to be designed to withstand harsh, snowy winters and warm summers. The biggest challenge that engineers face is how to use the soils that are present, because it is often too expensive to consider importing good soils. Engineers use what is called treatments or stabilization methods to modify the properties of those soils to withstand weather conditions.
How does climate change affect roadway construction?
Pavements are typically designed to withstand seasonal environmental changes assuming a certain pattern. However, climate change has brought us unpredictable patterns with harsher winters, heavier rainfall events, and severe droughts, which are not accounted for in the design.
What could happen if a road is poorly compacted?
If a road is poorly compacted, it can lead to problems such as cracking, bumpy roads, and in extreme cases, subsidence [or collapse]. These problems are of concern to general public because it results in road closures or detours for maintenance and cause traffic jams. One of the most important pieces of geotechnical engineering, which is the branch of civil engineering dealing with earth materials, is water. We need the right amount of water for compaction, but yet, it is vital to not allow water to enter the roadways after the roads are built. It is, however, impossible to completely avoid water entering the roads. Engineers design ways to drain that water away from the roads as soon as possible so it doesn’t weaken the foundation.
What would you suggest to a student interested in intelligent compaction/roadway technologies?
There is a bright future for people who have the skills to integrate fundamental knowledge in roadway construction with computer programming and sensor technologies.
Fun Fact: Did you know that the geotechnical properties of soils was critical in the NASA’s Mars rover expedition? NASA engineers have studied these properties over several years to design the unmanned rover’s traction system in a way to avoid getting stuck in the Martian sand.
By Jackie Nester, Go! Staff Writer