A Beginner needs HELP!

Hello I am a complete beginner when it comes to train modeling. I am doing a project for a class that involves modeling a construction site. Some of the work has already been done by a previous student, but my partner and I have had to take apart the model complete and rebuild a lot of it.

The model description:
rectangular area about 3'x5'
includes bridge construction site
tunnel construction site
building construction site
also includes roadway, river, and of course railroad
The model is HO scale

Some questions and issues I am working on right now:
Making a realistic "mountain" to have the tunnel go through. I have attached a photo of a mountain tunnel that I'd like it to look like.
making a realistic tunnel excavation
making a surface for the mountain and the rest that looks like it should (dirt and rock)

I purchased a lot of the pink insulation foam for the modeling.

Can anyone refer me to a resource or give me some tips? Any help is appreciated!

Thanks