Back-to-back and Chock-a-block

Back-to-back adverb - In succession without others coming in between.

Chock-a-block and back-to-back are semantically related. In some cases you can use "Chock-a-block" instead an adverb phrase "Back-to-back".

Chock-a-block adverb - As completely as possible.

Back-to-back and chock-a-block are semantically related. Sometimes you can replace phrase "Back-to-back" with "Chock-a-block", this phrases are similar.