What were the difficulties of building the St. Louis Arch?

Answer 1

From kozengagner.com: Sitework of the Gateway Arch grounds was extensive. Prior to the construction of the Arch hundreds of homes and businesses filtered the land and had to be demolished. The property was in rough condition. The site plan called for contoured, sloping land bringing forth a pleasant rolling park with tree lined walkways and reflection ponds.

Due to the unique nature of the Arch itself, designers were concerned the structure might be susceptible to high winds, so they conducted windtunnel studies. In combination with the studies and the original grading plan, a specific elevation at each end of the north-south walkway of 478' above sea level was determined, making them the highest two points on the Arch grounds. These hills actually protect the Arch, keeping high winds from putting too much stress on the structure. It should also be noted that designing the arch tram presented separate unique challenges. The tram needed to smoothly ride the arch's catenary curve, yet remain in a constant vertical position. The tram system also needed to be fully accessible for maintenance and repair.