There’s a large job near me where they are adding lanes and bridges to an existing busy highway. But, how in the world do drivers pushing dirt with gross precision get it right? I noticed I NEVER see surveyors periodically taking measurements, repositioning stakes, etc. to make sure things go as planned. In fact, I NEVER see an engineer working the beat along side the hardworking, blue collar men getting it done. And yet, it always comes out right (except for one incident in downtown Philly I recall in the 1980’s).
Granted, a road does not require as fine precision as making a Swiss watch, but if the grading is wrong, the road will pool (or, flood) instead of properly drain. And, so on and so forth. So, how’s it possible??? [Ok, roads DO pool, but you know what 'm driving at (no pun intended)!!!]
I used to work as a construction inspector. I was the “blue-collar” guy making sure it was done right. Surveyors and Engineers do show up occasionally, but my job was to make sure the stakes stayed in the right place when they weren’t there, among other duties.
ETA: In fact, I actually wore a “blue-collar” for part of the time, because the work shirts we got from the company one time were blue.
Back in the day, surveyors spent a lot of time doing cross sections of dirt work for subgrade, final grade, etc. I used to do this sort of work between college semesters. They still do, but it’s a lot faster with GPS technology. The bigger companies have GPS gear mounted directly on the grader blades, with a computer on board that automatically adjusts blade height on the earth mover. Pretty impressive technology, although it works toward eliminating jobs.
I’d say observation bias. Unless you’re watching the site 24/7 (unlikely) you may simply always drive by when the surveyors are not there. Did you notice any wooden stakes the road follows? Chalk or red spray paint marks?
There’s also the time factor: if (WAG here) the surveyor needs one hour to map out or check the measurements are still correct, but the actual road workers need 8 hrs. to pour the concrete/ flatten the bed/ whatever, then you have only 1 chance in 8 to see the surveyor instead of the road workers.
About observation bias: there was a nice anecdote about that (I think in Readers Digest?), about an office worker who watched a construction across the street. Every time he took a coffee break and watched the site, the workers were all standing around not doing anything, so he thought “What a lazy bunch, and I’m working my ass of here”.
But one day, he walked past the site after hours and happened to hear the workers talking amongst themselves: “See that office building over there? That guy in the window is always drinking coffee and standing around, he never works. Lazy bastards in offices.”
Only somewhat related to the thread, but I’ll throw it out there.
In case you are wondering why it seems to take forever before they actually poor the concrete or lay the asphalt it because whats under the surface is nearly as important (and perhaps arguably MORE important) as the surface itself. It need to be packed, the right moisture content, and a fair bit of other stuff before you lay down the surface material. Just smoothing the ground and laying stuff on it won’t cut it.
Subsurface materials and their placement are the most critical part of any construction, not just roads. If compaction, drainage or material is wrong, one can end up with all manner of problems, not the least of which is settlement or subsidence. In the Anchorage area, road specs called for 97% fractured face rock in the road mix. This was routinely waived for contractors because of cost, and round river rock was allowed as a substitute. Most roads in that city have permanent tire grooves, which can cause some nasty handling problems.
Jinx, Are you in the DC area? On the Virginia section of the beltway they are adding four HOT lanes in each direction. From bridge to bridge - Woody Wilson and American Legion. About forty miles of road.
Consider they are doing this while the beltway is in constant use, it will take around five years. Where they found room to add four lanes is difficult to conceive because in many places buildings and homes and roads, etc., are all in the way. It’s an amazing project.
But wait there is more.
Occurring simultaneously is the metro rail expansion to Tyson’s Corner and out to Dulles Airport. The Dulles Toll road intersects with the beltway, as well as the new rail line to form one of the biggest cluster f-bombs you will ever drive through.
I have to psych myself up everyday to drive through it as it is the only way I can commute to work. Tens of thousands of commuters doing a drive-ballet trying to safely negotiate all this construction and keep themselves and their cars in one piece. Supposed to finish in 2013.
My experience is with building construction, not road construction, but I think my experience is still mostly relevant in this case. The engineers typically are responsible for the construction documents detailing how the road needs to be built. The construction management team is then responsible for constructing the road per the construction documents. Sometimes the design engineer only does periodic inspections of the construction - the bulk of the inspection may be done by a separate construction inspector. So the engineer may not be on site, but the job is still being built to the design specifications.
Also, I’m not sure how you would tell if an engineer was on the site or not. When on site, engineers typically dress the same as other construction workers. So there may have been an engineer on site, you just couldn’t tell them apart from the other workers.
In the summer of 1980, I worked for an engineering firm in Honolulu, Hawaii. A few years before, that firm had lost a bid on a huge project to build a new elevated road to the Honolulu airport. The new road went over an existing highway.
If I remember the story correctly, the other firm was building the roadway from both sides, and planned to meet in the middle. However, they had miscalculated something and the road surfaces ended up being about 18 inches off. I think they had to redo quite a large section of the highway to account for the difference.
Our firm had every single newspaper article tacked up on a large wall, with their competitor’s name highlighted.
Engineers and workers look the same from the waist-down, more or less, but the engineers are the ones with the nicer, cleaner shirts (no T shirts, usually) and clean, white hard hats.
The ones with the hard hats covered in stickers (very obvious if it’s a union job), minor dings, and mud are the workers.
The ones who dress in between engineers and workers, but look like they’ve spent more time in bars than in school are the superintendents or owners.
The ones in nice shoes (with clean white hard hats), usually in a group, are the bankers/politicians/big owners.
Could someone start an “Ask the road construction guy” thread or something? They are renovating three major roads near my neighborhood and I have some questions! Plus I’d love to hear other people’s questions.
Pushing soil (engineers don’t call it dirt) around with a bulldozer or equivalent only requires fairly gross precision. Any significant movement of bulk soil doesn’t require very tight tolerances. The precision starts once they begin preparing the subgrade (the stuff below where the concrete will sit). So the precision starts with grading to get to the right surface elevation. Note that roads are typically built with crowns to allow water to drain off to the site - so the surface elevation will change across the width of the road. As others have noted, this is often done electronically with lasers and other equipment. This is where the major adjustments to elevation are made.
Once the grading is done, then layers of aggregate, compacted soil, etc. are added and compacted to the appropriate density. These layers, called lifts, are built to pretty tight tolerances. There will be QA/QC teams out there measuring the characteristics of the material being placed, and the depth, density and moisture content of the material being placed. These people will be dressed about the same as the other construction workers, because that’s basically what they are. They will run tests and typically have a mobile lab on site to test the aggregate and soil being used. Engineers will review this data and sign off as appropriate. This is where fairly minor changes to elevation can be made.
Pouring the concrete is the final step in a very long process. By this time, the elevation of the subgrade has been measured numerous times, and any adjustments made as necessary. The concrete pour itself can be made to fairly tight tolerances, although at this point there will not really be any changes made to correct for elevation. Those changes are made before the pour. There will also be teams of QA/QC people there to again test the materials being used to make the concrete (sand, aggregate) and the concrete itself (slump, moisture). Finally, the QA/QC people will collect samples of the concrete to test for strength at various cure times (number of hours/days after mixing the wet concrete).
I hope this helps some. Obviously - a lot has been left out. And of course, different types of roads are built with very different requirements - so the above can vary pretty significantly as well.
I am a surveyor, but I haven’t done many roading jobs. but the basics are:
The surveyor will do a lot of work right at the start, but has few visits from then onwards. They start by marking out the road with marker stakes that show both the position (Horizontal) and have markings on them to indicate how high or low the road is. The construction workers themselves use these marks to do a lot of the measuring themselves. Some bits of road might be a 500m stretch of road at a steady 2% grade or similar, and construction guys can do a lot of measuring themselves. A tight curve on a high speed road which needs to slope towards the inside of the curve is more difficult and the surveyor has to mark out more measurements.
The key job of the surveyor is to make sure that the construction lads know what to build and where. They get the plans from an engineer and transfer that to the ground so the workers can understand it. It’s very important to make sure everyone is on the same playing field because there are many ways to mark out a road. The surveyor also helps measure the volume of earth being moved because contracts tend to pay everything in rates (e.g $30/m³ moved)
A workmate once told me that career progression in an earthmoving company is that you start driving rollers and go through bulldozers/diggers, scrapers and finally graders - moving up in skill level each time. He also told me that grader drivers often had incredible ‘feel’ for the surface of the road and could tell when there were tiny fluctuations in the road that needed to be fixed. They also frequently stopped and measured - The contructors make much use of stringlines and builders optical/laser levels, and recently, machine mounted GPS so you can measure on the go.
OP, note that the surveyors, etc usually work normal office hours so if you don’t drive past during the working day, you won’t see them. Also, the traditional optical instruments are being replaced with high precision GPS systems that use a base station to get centimeter accuracy, so they look a bit different.
The skill of the grader drivers really is impressive as Jaguars! says. I remember twenty years ago my father had a local grader driver do our driveway (compacted limestone, about 500 metres, up hill with several curves and ‘interesting’ drainage issues) as a weekend job. After walking the drive once the whole job was basically done in one pass and aside from the occasional clearance of tree limbs and washouts hasn’t needed to be done since. I think those of us in office environments tend to underestimate the sheer skill that workers in the more physical trades possess.
There is always a deadline, and crews are almost always behind for one reason or another. Additionally, in northern climates it is critical to get all the projects done in the shorter construction season. Crews in Anchorage used to work 16-hour days in the summer.
They’ve been talking for years about fixing the street to my apt. Really horrific bumps in winter (Wisc.) and marshes around, altho worse bumps seem to be at the top of knolls. How deep will they have to put foundation to really fix it? 2-lane, no thru truck traffic.
An episode of Modern Marvels had a segment about using very dense styrofoam as an underlayer for roadways, that it would absorb the shifting and dramatically increase the life of the roadway.
