Is the oval really so big that they need to factor in the curvature of the earth?
short answer: no.
1) The topography
of the existing ground along the length of the oval is going to vary a lot more than a measly 2.4 mm
2) The track isn't being built directly on top of the the ground
3) Geodetic Surveying (accounting for the size and shape of earth) is typically reserved for huge
distances and benchmarking.. For a building this size, it would probably be less
accurate to account for the curve of earth, because the earth isn't even a perfect sphere.