Hi Steve.
I was plant operating...big offroad dump trucks, front loaders, backhoes (excavators).
One of the biggest problems they had on the airport was with water coming up through the ground, which consisted of millions of tons of rock just dumped into the sea and then covered with a few feet of sand.
There are a couple of big tunnel systems running under the runways ('cut and cover' types), so they had to build coffer dams along the length of the earthworks first to keep the water out.
Lots of other problems too..but wouldn't want to bore you.
That's what makes construction work so interesting though.
It was the biggest construction site in the world then. Finally having a total workforce of 20,000 when they were finishing it off and building the Terminals.
I also worked on a 'proper' 23km tunnel system over near Kowloon and the New Territories. Granite rock, with tunnel boring machines,etc, and running below the sea for part of the route.
Now that project REALLY had some problems.

Great job though, if damned hard graft.
Here is one of the tunnels going in on the airport. It finished up being about a quarter mile long, and included a roundabout inside it.

Looking directly ahead you can see the main Lantau Island.
There WAS a little village just across there until the mid-90s. That is almost a mini-HongKong now....such is the incredible rate of development in both HK and mainland China.