As there is so much change in the market, and competition for projects, as a junior engineer you can often end up being swept around, forgotten, lost in the blur of the busy workplace. It's not uncommon for junior engineers to have literally nothing to do, and I've seen very intelligent junior engineers sitting around for months on end doing literally nothing. One friend of mine sat at his cubical for an entire year with no real work to do.
But as long as your hours are being billed to the client, nobody really cares whether or not you're actually performing. This can be immensely discouraging, especially if you're bright and ambitious to learn.
Since there is a lot of turn-over in this type of company, you may also have the experience that you're constantly re-establishing and re-proving your skills and your worth. You may get a new boss every 3 or 4 months, and what's expected of you can be very vague.
HR puts a lot of work into trying to guide your development, and put you on the path of honing your skills and improving your knowledge, to better perform. But don't fall into that trap - the reality is that these "Jacobs Future" or development programs are more or less useless. The key to succeeding is in developing connections and relationships with people directly in the company. Use honesty, be ambitious, but be patient.
Overall, Jacobs is quite a decent company. I'm not sure that I recommend it to junior engineers, especially if you are in civil / structural. As a civil / structural engineer, you need a lot of hands-on and field experience to understand the concepts and know what you're doing. At Jacobs, you'll likely get zero, as the construction contractors are typically a wholly other company.
I left after 2 years, having decided that I didn't like the big-company Dilbert-style of career. Best of luck.