Obviously here in Smaug’s lair, Tolkien means that the benches are toppled.  I am intrigues to learn that the word can also mean “rotate” as a wheel, to fall to grief or ruin, or to disorder a stomach.

• 13.046 and benches were lying there overturned,

“overturn, v.” OED Online. Oxford University Press, June 2015. Web. 14 July 2015.

While there’s the figurative meaning of casting one’s opponent out of a position of influence, there’s a less common literal meaning of throwing someone over onto their backside on the ground.  I’m certain both images work here.

• 18.042 and the goblins overthrown,

“overthrow, v.” OED Online. Oxford University Press, June 2015. Web. 14 July 2015.

In this meaning, overtake used to mean “catch up with” not “catch up with and pass”.  Interesting!

• 08.120 and fight the creatures that were overtaking them;

Overshadow is used in its literal sense of a shadow passing over.

• 01.122 overshadowed by the Mountain.
• 09.061 There was a dim sheet of water no longer overshadowed,

The strategists in the Battle of Five Armies plan to lead the goblins between the spurs of the mountain unless they are so numerous as to overrun the Mountain.  Here we have both the spatial sense of running over the surface to cover it and the superiority sense of being most powerful.

• 17.045 to overrun the Mountain itself,

“overrun, v.” OED Online. Oxford University Press, June 2015. Web. 14 July 2015.