This how I raid beaver dams in ark:
First you should get a trex or some other tall, aggressive Dino. You will need them to hop on and escape or to kill the angered beavers. I recommend taking the cementing paste, peals , flowers and mushrooms first, depositing them in a chest then getting the wood. Since wood is heavy, drop it after picking it up. Once all items are taken from the dam it will break and the beavers will build a new one.
How to build dam farm:
12 foundations (preferably stone)
12-24 doorframe (preferably stone)
1)find an already existing dam
2)build a 3x3 box around the dam with fence foundations
3)place doorframe on top of the foundations;if the dam is underwater, put enough layers for the top doorframe to be out of the water
4)using an argie, pick up 2 to 3 beavers and drop them into the box. 2 is the minimum number needed for them to spawn a dam but I find that 3 works better. (note:if you want more dams, bring beavers from another spawn location as no more beavers will naturally spawn in that area. Its also preferable to build another box so they don't end up pushing each other out the top)
Dams will spawn around every 12 hours
Remember to not leave the items you don't want in the dam. Drop them so that the beavers can spawn a new one without having the dam demolish after a week.