Determiners are words like: a, the, this, that, my, your, no, one, two, many, much.
If a noun already has a determiner, we can't also use the determiners much or many with that noun:
- *much the work, *much our water, *much which water (ungrammatical)
- *many the people, *many my friends, *many these people (ungrammatical)
We also cannot use much or many with pronouns:
- *many them,*many us, *much it (ungrammatical)
When we want to use much or many with these phrases, we need to use a preposition phrase with the preposition of:
- much of the work, much of our water, much of that paper
- many of the people, many of my friends, many of these animals
- many of them, many of us, much of it
If the noun doesn't already have a determiner, we do not need to use the preposition of when we use the determiners much or many:
- much time, much water, much effort, much paper
- many people, many friends, many animals
The Original Poster's example
In the Original Poster's example they use the uncountable noun administration without another determiner apart from much. Because of this the OP doesn't need to use the preposition of:
There is so much administration to do.
*There is so much of administration to do. (ungrammatical)
However, if they wanted to use another determiner with the noun administration, then they would have to use much of. Here are some examples with the determiner this:
*There is so much this administration to do. (ungrammatical)
There is so much of this administration to do.
Hope this is helpful!