Spigot/bukkit's chunk loading system is does not function as intended.
Chunk.isLoaded() will always return true because World.getChunkAt() loads the chunk.
Therefore Chunk.load() does nothing.

Chunks cannot be kept loaded by cancelling a ChunkUnloadEvent. This is strange because if there is a redstone clock on the chunk, the chunk will stay loaded if the event is cancelled.

However, if all ChunkUnloadEvent's are cancelled, then the chunks will remain active.
If the chunks do not have a redstone clock, they will not actually load until a player is close to them.

I used a minecart to test this.