3d drawing how can I slice using a freeforming polyine,arc,curve line from topograph

Hello,

I have designed a layout of a mine for my company. Now i have to slice the shape i have created 30m in from the edges. The edges have a radial contour, so i dont wanna end up doing 20 slice cuts, then union back the pieces to create two seperate pieces. This will still look choppy and produce bad numbers for volumes. So anyone know how i can go to topographic draw a polyline on top of the 3d shape and use it as my slicing edge?

P.S I have made a polyline and extruded through the shape, then used slice>object select but it comes up with no result. I have managed to slice in topograph and even in 3d views but NO MORE SHARP LINES

So you solved your own problem? Yes? No? I'm not sure?

I might have used the slice with surface option.

no i wanna make a curved slice cut, NOT straight line slices