I want to take down a retaining wall made of railroad ties. There are large spikes holding the ties in place. I need to know how to remove these spikes.

Let's look at how it's constructed: How to build a retaining wall with railroad ties - by Tammy L Mahan - Helium

Those spikes are rebar. They don't cut easily and they are not smooth.

I'd be tempted to use a large flat chisel with a hammer drill and a couple of crowbars to remove tie by tie.

I might also consider a pair of hydraulic jacks.

Railroad ties can have some nasties in it like arsnic and may have to be disposed of as hazardous waste.

There is such a thing as retaining wall spikes.a crowbar has a claw on the curved end like a hammer you should be able to pull them with that.you may have to pry the top tie up a little to pop the spike up a little so you can get the claw on it or drive the claw under the head with a hammer.if it is rebar then drive a wedge under the top tie so you can get a sawsall in and cut the rebar or try to pop off the top tie with the wedges and crowbar then bend the rebar with a long piece of pipe ,sledge hammer so the crowbar can get a grip

Tie spikes are 12 to14 inches long. Usually 4 spikes to 8 foot tie. Pry top tie up high enough to get metal sawsall blade in. Cut spikes and remove ties one at a time.

To pry these out u would have to use an 8 foot wrecking bar. Also would need to raise the bars foot as u pull spike.

Good luck

Chuck