RW15_constrain model based on ground surface

[temelsu]

Hi everybody,

While we are creating our stratigraphic model, we want to define ground surface from a dxf file. The first question is how to convert .dxf file to .grid file. We followed the instruction but program gave an error in each application.

Somehow, we managed to convert our .dxf file to xyz data sheet and we created our grid file for ground surface.

The second and more important question we come accross is here actually: We have stratigraphic layers defined by borehole data. When we create our model without checking the “constrain model based on ground surface” option, the boundary conditions of our model are seen as acceptable. However, the surface condition is not similar to our real condition; in other words it is not acceptable. So we checked that option (constrain model based on ground surface), defined it by our previously converted .dxf file and we also choose the “truncate units above ground surface” & “replace topmost surface with ground surface grid model” options. However, in this case we got a model which have acceptable ground surface condition (by the way, when we import our original .dxf file on to model we see that they do not match properly but they are at least close to each other) and nonsense stratigraphic design. Our topmost stratigraphic layer extended up to newly defined surface without saving its thickness we had defined in borehole data.

As a brief summary; I want to create my model based on my borehole data and define its ground surface with an adaptable imported file (eg., .dxf file). However, as I tried to describe I have some problems with it. So I need some help urgently. So if you help me soon I will be appreciating.

[Molly]

The "replace topmost surface with ground surface grid model" option tells the program to discard the surface it interpolated for the top of the uppersmost unit from your borehole data, and to use, instead, the imported ground surface model as the top of that unit. If you activate this, then the borehole thickness information will not be considered.

The "truncate units above ground surface" option simply tells the program to constrain the top of the uppermost unit from extending above the ground surface grid.

The easiest solution for visualization would be to activate the "truncate" option, to prevent the interpolated surface from extending above-ground, to de-activate the "replace" option, and then to simply append the ground surface to the stratigraphy model in RockPlot3D to illustrate the true topography. (To generate a 3D display of the ground surface grid, just double-click on the GRD file name in the project manager and choose Create 3-Dimensional Grid Diagram. Save the view in RP3D. In the RP3D view of the strat model, choose File / Append to append the surface's .R3DXML file to the model.)

If you need to replace selected portions of the interpolated surface with the ground surface, this gets more complicated. I'd need to see the data.

To get your DXF contours into RockWorks as a GRD model, I think the method you used is correct: File / Import / DXF into the Utilities datasheet, then Map / Grid-Based Map to interpolate a grid model from the contour endpoints, using the project dimensions. The accuracy of the resulting surface will depend on the spacing of the nodes, the detail of the topography, the gridding method, etc.

Molly Mayfield

RockWare Inc

molly@rockware.com

[Molly]

You might also refer to a case study on our website, "Adjusting DEM Grids to Fit Measured Elevations" if you wish to adjust your topography grid to borehole elevations and then use that for the upper strat surface. This paper can be found at:

http://www.rockware.com/assets/products/165/casestudies/8/6/dem_case_study.pdf

Or just go to the RockWorks section of our website, and browse through the Support options in the left-hand menu.

Molly Mayfield

RockWare Inc

[temelsu]

Dear Molly,

Thanks for your reply. We have just tried the things you mentinoed whereas we were not able to fit the ground surface to our top of stratigraphy model. There was a gap between ground surface and stratigraphy model. In addition, some of our boreholes extend above the ground surface, though the ground surface elevations and borehole elevations are ok in our CAD drawing. We are trying to model a dam site with the borehole data available. Is it possible to send our data and let you to look at it?

Regards

[Molly]

Of course. You can zip your project folder and email it to me (molly@rockware.com). If it's too big to attach to a message, please send me an email with this information, and I'll reply with the instructions for uploading data to our guest site.

Molly