The railroad serving your customer should have a standard plan. However, once you encase the rail in concrete maintenance becomes an issue as you need a jack hammer to expose the rail and fastenings. You may want to condiser a rubber flangeway filler that would pop in and out to allow track...
This is not as easy as it sounds. Railroad bridge replacements are normally performed under traffic. If it is a high density freight or critical passenger corridor then you will have limited opportunity to take the track out of service. Therefore your design must consider construction in...
Ususally those manufacturers are quite willing to share their data especially if you are trying to solve a problem. The best way in usually is through their sales contacts.
Drilling is preferred to torch cutting and you want to stay as close to the center of the web as possible. Can you guess at the wheel load of the doors?
AREMA publishes the Talbot reports where they explored track reactions to loading. A quick flip through the book did not give any high level math. What's the context of your problem?
Most PE review texts have a pile section as well as books such as "Foundation Analysis and Design". However, these are all on the design side. You may want to search the web for tips from the major manufacturers.