I got 1 across while I was printing it out but after that......
9a somewhat resembling how the Burj Khalifa was constructed? --/--/a/-o---
12d Who sings? Smooth Rat Pack member, Sinatra to start with ----/--r---s
I think you’re right, Vivian, especially about the Rat Pack clue. The clue ‘Who sings ...’ suggests a singular answer - and I’m not even sure that Sand Martins are renowned as songbirds!