how to determne grade for a new driveway

[/pine]

I think I have a plan. Actual grade will depend on total distance. I Think I can put together a 50ft water level and start with the 4% number on one end and just see how close it comes out at the other end. The 50ft stations will give me a total distance traveled, and I can then just measure the difference in the end results and the desired results and make the needed adjustments for a final centerline. Once the centerline is flagged I can then use the water level to determine the heights of the high side cuts and lower side fill, based on the width of the road. This should give me some ideal as to how much timber needs to be removed. This is something I can do without waiting for another person to help.

As for the topo maps being accurate or surveyed, they probably havent had a actual physical measurement made. I dont know what kind of device or instrument those mappers use to come up with their numbers. I do know that trying to use a sight inclinometer, and guessing at slope wasnt working. To much changing directions and correcting grade to get where you want to be. If it wasnt for going around a hill side, the inclinometer might have worked pretty well, but its hard to sight around a curve.

How can you get 50' stations with just a 50' hose?...a water level usually requires two people...IMO an optical level is easier to use if you have a rod man...

 

[s219]

The contour lines on topo maps aren't all surveyed. They may not be as accurate as you'd like.

Very good point, if done from aerial imagery then they are an approximation with low accuracy and low resolution. They will skip or blend over all sorts of features when they render the contour lines. These are more like approximate 3D models (with plenty of math) rather than actual surveys (with plenty of data).

When we were buying our property in 2011, I was walking the land and darn near fell into a ravine with a creek. Wasn't on any map anywhere yet it was 8-12' deep in spots and ran diagonally across the property (cutting a rectangular parcel into two triangles).

Later when we got the land surveyed, I asked the surveyor to make sure he got some measurements of the ravine since it was a very prominent feature. He at first acted like I was being picky, since his company had done the development plan for the land 5-10 years earlier and he thought they did a pretty good job with their base map. I think he was just going to import those contours and use them for the new survey plat. Well he called me up afterwards and was almost euphoric that it was indeed a land feature and was missed. His surveyor got 4-5 readings across the ravine in 10 locations and it made for some nice contours.

One suggestion, which I have used in challenging situations. Estimate an approximate grade best you can, perhaps based on constraints or requirements, and then build the road to that grade. Make it work. I have used this approach twice when building stairs on a 40' bank. Good luck trying to measure accurate rise/run on a steep bank. Instead, I got a rough estimate, decided on the stair pitch I wanted (for easy walking and safety), and then made it work. Stairs are somewhat of a math challenge since you have a fixed integer number of identical steps, but we're talking about steps that are 5-7" high and over 40' that gets lost. Build from the bottom up, and at the worst, the top step will be off +/- 2.5-3.5". If below the top grade, go up one extra full step to be above the top grade and then use dirt to make up the difference.

Obviously a road is more complicated than steps, but use the same line of thinking. Get a rough idea, consider constraints and requirements, and then make the road do what you want. Dictate the grade. Move dirt to deal with the little nuances.

 

[Egon]

Hand Level, 100 ft. Chain/tape, a six foot long piece of 1x2 marked in ft &. Tenths, a piece of Keel, bundle of lathes and a hammer is all you need.

Run an offset line of stakes you can reference to and you are all set.

 

[mapper]

The contour lines on topo maps aren't all surveyed. They may not be as accurate as you'd like.

The accuracy of the contours depends on the DTM data that is used to generate them. If they are derived from 15' USGS quad maps then they can have considerable error when there is heavy tree cover. Within the last 15 years or so many state, federal and local agencies have been upgrading their DTM data using aerial LIDAR (laser tech) this data is usually very accurate even under tree canopies.
You may be able to find out from your county website where you got your contour data from, look for a way to access the metadata. That should tell you what was used to create the DTM data layer. Or perhaps the easier, call your county GIS or geodata office and ask them.
I spent nearly forty years in photogrammetric and LIDAR mapping, answering questions about map accuracy was part of the job. You have to know how the data was created and what the required accuracy was for the data when it was collected. Until recently very high accuracy data also carried a very high price tag, technologies such as GPS, digital photography and LIDAR have changed that to some extent.

 

[muddstopper]

How can you get 50' stations with just a 50' hose?...a water level usually requires two people...IMO an optical level is easier to use if you have a rod man...

50ft is 50ft. I will probably buy a 100ft hose to make the water level and just keep 50ft coiled up Doesnt matter is you use a tape measure or a water hose. I have a ton of experience laying out curves. The surveyors would make 100ft stations and stake it out that way. This is fine if you have clear line of sight. Even once they had the curves laid out in 100ft stations, I would go back and make corrections at 50ft intrevals. It had more to do with keeping all measurements within the limitations of the measureing equipment I had to use. You would be surprised at how many times I would fine errors in the surveyors measurements. When you graph it on paper and there is a obvious deviation in the connecting dots, its easy to see someone made a mistake in their layout. I dont have access too any fancy equipment and I dont have readily available help to do the layout. A water level can be one man friendly. You set your starting point, calibrate the water level and then just take the other end of the hose and start walking. Once the next station is located, you just move the whole water level up to that station and do everything all over again. Going 50ft per station in a wooded area, it is easier to keep a line of sight. Knowing that each station is a set number of feet also give a pretty accurate total for the number of feet traveled. When you are paying for grade work by the linear foot and power lines cost a set amount per ft. You can get a pretty good estimate of the total cost. Right now I am baseing my cost estimates around best guesses. I am guesstimateing around $40k to build the road, install power, septic and well. road building and power are a large part of that estimate so cutting the lenght of the road by as much as possible will result in a big savings.

Similar results can be had by using a lazer level and tape measure. This method is best used with a known amount of degrees. Stations would be setup at 62feet and deviations measured at 31ft in the middle of each station. A 1 inch deviation is one degree . This is a cordial curvature and is done using a 62ft cord. It takes three people, one on each end of the cord and one in the middle doing the measureing, or a lot of walking to use this method. Most surveys are done on a radial curvature where a transit is just turned a set amount of degrees and linear measurement are made to establish the next station. Most surveyors just scratch their head when you mention a cordial curve.

 

[jmc]

Extend a level by mounting it to a 10 ft 2x4. Mount it near what will become the downhill end of your extended level, where you can see it when you take vertical measurements.

Starting at the bottom of your route, put the uphill end of your level on the path, level it, and measure the vertical gap on the downhill end. (Rise)

Rinse and repeat sequentially so that you have a series of rises every 10 horizontal feet up the path. (End to end chain of measurements.)

Add up all the rises, count the number of 10 foot runs and you have an exact total elevation, a close approximation of the driveway length, and the slope of each 10 ft driveway segment.

I did this and with my child writing down the rises, it took about an hour for 900 feet.

You can do something similar to pick a path by keeping the rise within your acceptable grade range and pointing the leveled 2x4 in a promising direction where the uphill end touches the ground.

 

[/pine]

50ft is 50ft. I will probably buy a 100ft hose to make the water level and just keep 50ft coiled up Doesnt matter is you use a tape measure or a water hose. I have a ton of experience laying out curves. The surveyors would make 100ft stations and stake it out that way. This is fine if you have clear line of sight. Even once they had the curves laid out in 100ft stations, I would go back and make corrections at 50ft intrevals. It had more to do with keeping all measurements within the limitations of the measureing equipment I had to use. You would be surprised at how many times I would fine errors in the surveyors measurements. When you graph it on paper and there is a obvious deviation in the connecting dots, its easy to see someone made a mistake in their layout. I dont have access too any fancy equipment and I dont have readily available help to do the layout. A water level can be one man friendly. You set your starting point, calibrate the water level and then just take the other end of the hose and start walking. Once the next station is located, you just move the whole water level up to that station and do everything all over again. Going 50ft per station in a wooded area, it is easier to keep a line of sight. Knowing that each station is a set number of feet also give a pretty accurate total for the number of feet traveled. When you are paying for grade work by the linear foot and power lines cost a set amount per ft. You can get a pretty good estimate of the total cost. Right now I am baseing my cost estimates around best guesses. I am guesstimateing around $40k to build the road, install power, septic and well. road building and power are a large part of that estimate so cutting the lenght of the road by as much as possible will result in a big savings.

Similar results can be had by using a lazer level and tape measure. This method is best used with a known amount of degrees. Stations would be setup at 62feet and deviations measured at 31ft in the middle of each station. A 1 inch deviation is one degree . This is a cordial curvature and is done using a 62ft cord. It takes three people, one on each end of the cord and one in the middle doing the measureing, or a lot of walking to use this method. Most surveys are done on a radial curvature where a transit is just turned a set amount of degrees and linear measurement are made to establish the next station. Most surveyors just scratch their head when you mention a cordial curve.

Bill, I'd never doubt your expertise...this thread takes me back to the college classroom for "route location and design"...Never did understand why they made us study RR design as well as vehicular highways...but it was fun learning how to design and draw station maps when the curves had super elevations...(used to be a lot of that on 76 until they straightened and flattened it out)

One challenge you might run into is keeping your station pins and grade stakes etc. out of harms way but still close enough to your cut lines to be useful...

Hope you start posting some pics as soon as work is underway...

 

[muddstopper]

While I had considered a water level back when I first tried to layout the road, I had sort of dismissed the ideal. It took JDAOWNER mentioning it again for me to really start thinking about the ideal. It will work, it just might take me a few trys to get the exact slope, but measureing out the distance and elevation and putting it on a graph should put the grade dead on. Once the road is laid out, I can use the water level to determine how deep the cuts will be and how much fill I will have. This should give me a good ideal of just where and how much timber will need to be removed.

I bought a bunch of those little flags I will layout the centerline with and the width boundries. I will be sure to take a few pics once I get the flagging done an as the road building progresses.

 

[brian3180]

While I had considered a water level back when I first tried to layout the road, I had sort of dismissed the ideal. It took JDAOWNER mentioning it again for me to really start thinking about the ideal. It will work, it just might take me a few trys to get the exact slope, but measureing out the distance and elevation and putting it on a graph should put the grade dead on. Once the road is laid out, I can use the water level to determine how deep the cuts will be and how much fill I will have. This should give me a good ideal of just where and how much timber will need to be removed.

I bought a bunch of those little flags I will layout the centerline with and the width boundries. I will be sure to take a few pics once I get the flagging done an as the road building progresses.

How did using the water level go?