Q.1. Why not just overlap the steel wire armour strands and connect them with a big connector like the live cores?
Q.2. Why not provide an air vent hole to let the air out that would aid the filling process. After use the air vent hole could be capped off with a push fit cap.
https://www.bing.com/videos/search?q=youtube+underground+cable+jointing&docid=608005191810220304&mid=B35A506FF48B038CEFEDB35A506FF48B038CEFED&view=detail&FORM=VIRE
Z.