site survey problem

Hi all,

I have AutoCAD 2011

I have been asked to work our a volume of a mound of earth my company have to install on. It backs onto a fence line and is a huge mound. They have taken all the levels for me, but they want me to work out how much volume of earth needs to be remove from the top of the mound and put at the back to fill up the gap to then create a flat top to the hill to install on.

Firstly is this something i can do on AutoCAd or do i need some sort of survey software.

If it can be done on my software, how to i create a 3D solid shape of the mound and find out the volume of the gap i hvae to infill.

Apologies if this seems a silly question to ask but i have never had to do this level before and I've only recently got the full version of AutoCAD so still learning the extra stuff it can do.

Thanks

Sarah:?

This is something for which you need AutoCAD Civil 3D. As far as I am aware vanilla AutoCAD is not capable of doing anything like this.

Check out this tutorial http://www.cadtutor.net/tutorials/terra-firma/index.php to see if that offers any help. Alternatively, you could download a 30 day trial version of AutoCAD Civil 3D if you only need it this once, or if you might need it more often you have the chance to evaluate it.

thank you i will try the download i think

I'm not a civil guy, but if you have the survey points, you can create the contour lines, then loft them to create a solid, then slice off however much you need for the landing.

Could you explain how i 'loft them to create a solid'?

 

I'm not a civil guy, but if you have the survey points, you can create the contour lines, then loft them to create a solid, then slice off however much you need for the landing.

 

Nestly how do you create your contour lines in vanilla AutoCAD? The cut and fill exercise, if I understand Sarah right, is an unknown quantity at the start and she has to work that out. The more she slices off the top and dumps in the hole, the smaller the hole is, until the hole is filled and she has a level platform.

I assume the 3D points are available in AutoCAD since she said "they have taken all the levels". If that's the case, I'd filter the elevations and use a polyline/spline to create a close approximation of the contours. After lofting the plines/splines to make a solid, there will be a known quantity above, and below the slice point. I'm not suggesting AutoCAD is the best tool for earthwork, I was just offering a method to solve the problem with tools she has.

I've not much experience with lofting but can you loft a polyline/spline with different Z-values on each node, I don't know. I think the 3D points she has will have been randomly surveyed/levelled and will not have nice even Z-values, if that is the case though your method would be ok to create a solid.

Sarah never mentioned accuracy or bulkage/compaction of the excavated/filled materials.

A bit further explanation, my sales and ops men went on site and hey took levels from a datum point every two metres across the cross section of the mound and did this every 4 metres along the length of the mound, so in autocad i crew all the cross sections of the levels at the correct intervals, so i have a very basic idea of what happens to the levels. Hence I have cross sections and a very crude idea but now need to show outside contractors how much landscaing and earth movement is required to infill the rear of the mound to flatten the top of the mound for installetion of play equipment.

From what you have there it looks like that you have contours, so nestly's idea would work to create a solid. How did your guys create the contours. If they have software to create the contours then they could well have software that will do the cut and fill exercise.

When you say you want to slice off the top of the mound and infill at the rear of the mound, will the rear of the mound have an embankment with preset slopes, or a retaining wall. How accurate do your figures need to be? I know some companies who give that job to the contractors and just indicate a ball park figure when tendering.

It looks like you already have your contour lines drawn at the proper elevations, right? Is there a retaining wall along the rear of the mound at the tree line/fence.

Assuming those contours are closed polyines or splines, just use the LOFT command and select the contour lines in order (from the lowest to the highest) and your mound should become a solid object. You'll need to create another solid in the in the rear you can use to subtract the mound from to determine the amount of fill needed. Then it's going to be trial and error slicing off the top of the mound so you have an equal volume removed from the top as you need to fill along the rear.

If you're not already familiar with 3D solids, I'd refer to your AutoCAD help files for Loft, Subtract, and Slice, and of course, MASSPROP (and/or MeasureGeom) to find the volume of the solid(s)

No, unfortunately the contours were already there from a previous dwg sent to me by an outside surveyer from when the school was built. The contours are not accurate in size hence the fact that my sales/ops team have gone back to re-measure the mound.

The rear of the mound will have a retaining wall. Im hoping my figures don't need to be too accurate. I'm showing them cross sections as they are and then what level I think they need to be brought down to for the equipment to fit on the top. The question is then whether the soil they move will fill in the rear sufficiently or will there be soil that needs to be removed off site.

Thank you for all you suggestions......I'm sure i will be able to get them a close enough idea for them to tender with.

it sounds to me like you only need an estimate. are you sure you're not wasting your time by trying to get more accuracy than is necessary? if the cross sections do not vary too much, take one and multiply it by the length - is this not enough? better still, average the sections' areas and multiply that by the length. i didn't think earthworks was a precise business. besides, compaction etc as above will ****** up your precise calcs anyway.

BTW, don't forget to update your profile if you've moved from the LT to the full version. :wink:

Thank you to you all who have helped me with this, i have at last got them enough details and information that the outside contractors can accurately tender for this job.

I havent done the calculations for them, just given the cross sections and the slices that we need to excavate down to and the area which they need to fill. Will leave it up to the experts themselves to calculate this taking into acount compaction etc.

Much appreciated everyone

x