Road construction take long time ? Because

Road construction take long time ? Because

From rugged dirt paths to modern super highways roads are one of those consistent background characters in nearly every person’s story. And, if you’ve ever been a driver, I know another similar character in your life road construction. Most of us love having wide, smooth roadwaysto take us to work to home and everywhere else we travel. But, we’re hardly ever excited to see aconstruction project starting on our favorite roadway. I’m here to change that  or least to try. I love construction  always have and whenit happens along my commute, I love it even more because I get to see the slow but steady progress each day. And, I think  or at least I hope  that ifyou can know a little bit more about what’s going on behind those orange cones, you might appreciate it a little more as well. we’re talking about earthwork for roadways. The first roads in history were probably formedas people or animals followed the same trail long enough to tamp down the vegetation andestablish a route between two points. But that’s not enough for the roads of today. 

Why? 

Because the earth is full of irregularitiesthat aren’t conducive to safe, efficient, and convenient travel. There’s a reason we have the distinctionof off-road vehicles. ATVs and dirt bikes are fun, but most of usdon’t want to wear a protective bodysuit for our daily commute. Safe and efficient travel means smooth curves,both horizontally and vertically. It means grades that aren’t too steep, andit means paths that are relatively direct between points of interest. In a very general sense, that means to builda roadway, we need a way to smooth out the surface of the earth. A lot of people use words and writing to communicate. But, roadway engineers and contractors usethe cross-section. This is a special kind of drawing that showsa slice through a particular location, and it’s the literal language of road building. On it, you can see the level of the earthbefore construction, and the proposed surface afterward. 

Any difference in these two lines means someearthwork is going to be required. Areas above the proposed roadway need to beexcavated away also call cut. And areas below the proposed road need tobe filled in. Cut and fill are the most fundamental conceptsin any earthwork project. And keeping cut and fill in balance withone another is a critical part of roadway engineering. After all, if you need to fill in some areas that soil is going to have to come from somewhere. Rather than importing soil to a project, itmakes a lot more sense to take it from somewhere that already needs it removed. And if you’re going to have to excavatetons of soil from some part of your project, it sure would be nice if rather than havingto dispose of it, you could take it to some other part of your project that needed additionalmaterial. If the amount of cut and fill on a projectis balanced, every shovelful of dirt is doing two jobs taking soil away from where it’snot needed, and gathering soil for where it is. So, engineers designing roadways keep trackof these quantities between each cross-section. Of course, earthwork may seem simple whenyou’re just looking at a drawing, but here are a couple of things to keep in mind: soilis heavy, and roads are long. Just because you have the same volume of excavationas you have fill doesn’t necessarily lead to efficiency. Because if all the cut is miles away fromall the fill, you’re going to have to make a lot of trips. 

So, roadway design not only needs to balancecut and fill but also try to minimize the haul distance. Mass haul diagrams show the net change inearthwork volume over the length of the roadway. This gives the pros a quick understandingof the amount and distance of earthwork for an entire roadway project. But we’re still not there yet. Because, once you get all the soil in theright place, you can’t just build a road on top. I’ve said it before, and I’ll say it again:Soil’s not that strong, especially in loose piles fresh from the bed of a dump truck orscraper. We have to compact it down. But, even that’s not so simple. There may be no other material more tested than soil - maybe blood, but if you measure by weight, I don’t know. In testing labs all over the world, probablyat this very moment, there are people looking at and taking pictures of, shaping and rollingsoil, inserting it into equipment, taking measurements and writing those measurementsdown on clipboards.

Why?

 Because soil is really important. The cost of building roads varies from placeto place, but very roughly, it’s about $3M for a mile of 2-lane roadway. That’s about $2M for a kilometer. Roads might be the most expensive thing youtouch in a typical day because they take a lot of work and a lot of material to build. So if we’re going to go to all that expensejust to make it easier to drive our cars from place to place, we need to make sure thatthe roads we build have a good foundation. That mainly means proper compaction. Soil settles and compresses over time, andif this happens with something on top (like a road or any other structure) it can leadto damage and deterioration. Compaction speeds up that settlement processso it all happens during construction instead of afterwards. If soil is compacted to its maximum density,that means it can’t settle further over time. 

how do we know whether it’s compacted enough? 

That’s where the testing comes in. Soil labs do a ubiquitous analysis calleda Proctor test. If you add different amounts of water to soiland try to compact it, you’ll see that you get different densities. With low moisture content, it’s nearly impossibleto do any compaction—same thing with high moisture content. But, somewhere in the middle, you’ll getthe maximum density. This estimate of the maximum density is oneof the most crucial measurements in earthwork. There are a few ways to test density, but we mostly use nuclear gauges that measure the radiation passing through the soil toestimate its degree of compaction. Soil used for filling areas is first placedin roughly the correct locations by a dump truck or scraper. Then it’s smoothed into a consistent layer,called a lift, by a bulldozer or motor grader. Finally, each lift is compacted using a compactor. This is at the heart of why earthwork takesso long to complete. You can’t compact soil more than arounda foot at a time (that’s 30 centimeters). Rolling over thicker layers will only compactthe surface, leaving the rest lo and free to settle over time. So areas of fill, and especially tall embankments(like the approaches to a bridge), need a lot of individual layers. By necessity, they come up slowly little bylittle, lift by lift. Every so often along the way, someone doesa test to check the density of the compacted soil. There are a few ways to test density, but we mostly use nuclear gauges that measure the radiation passing through the soil to estimate its degree of compaction. We compare that measurement with the maximum density measured in the lab. If it’s close, it’s okay. If not, we keep compacting until it is. 

That gives engineers and contractors the confidencethat when the roadway surface is placed, it’s going to be there to stay. But, it’s one of the biggest reasons thatroadway projects take so long to complete. We can move a lot of earth quickly, but to place and densify it into a foundation that will stand the test of timeis a process, and it doesn't happen right away. One last thing I want to point out: duringthe construction of a roadway (or really construction of just about anything), this earthwork causesa lot of disturbance. What used to be grass, plants, or some othertype of covering over the ground is now just bare soil. That may not seem like a big deal, but toall the aquatic wildlife in nearby creeks and rivers, it is. That’s because any time it rains, all that unprotected soil gets quickly washed away from the construction site into waterways where it reduces the quality and quantity of habitat. So, pretty much every construction site yousee should have erosion and sediment control measures in place to keep soil from washingaway. Silt fences and mulch socks slow down runoff so the sediment can drop out, and rock entrances knock most of the mud off the tires of vehicles before they leave the site. Like it or not, roads are part of the fabricof society. Travel is a fundamental part of life for nearly everyone. Unfortunately, that means road constructionis too.