You have been busy creating all those validation rules. :-)
There is no limit. You will not be able to find anything in the documentation because there is no limit for two reasons: 1) it is a normal table so it can grow up to its physical limits; 2) no one has ever needed so many validation rules.
Take performance into consideration. Each validation rule takes up a small amount of time every time you commit an object.
Why would you like to do that?