missed pipe blockout in stormwater pit

[Sang_12345]

Need technical guidance!
During a concrete pour of cast in-situ pit, we missed to include a blockout for pipe penetration. One pit has been designed for 100 years design life and other for 50 years design life. What can be most suitable solution to create an opening for 750mm (in 100 years design life pit) and 450mm (50 years design life pit) pipe opening in the pits? The applicable standard- Australian standard.

Furthermore, are trimmer bars and U bars at the opening for the pipe required?

 

[Tstruct]

If possible make multiple openings instead of one big in between the spacing of the steel mesh.