31 minutes ago, Dr B said:

I apologise. You obviously know far more about this than I could ever hope to. 

Would you be good enough to help me by drawing a cross-section through the sinkhole, about 30 m across at the top and about 17 m deep, and then show me how you would:

1  Excavate and stabilise the hole

2  Fill it with layers of large stones, gravel and soil compacting each layer as you go from the bottom up

3  Where you would place the concrete, rebar and a geotextile fabric

I am eager to learn.

i do not get paid to teach so do your own research 

31 minutes ago, Dr B said:

You were the one saying that it was essential to place the fill and compact in layers. I was showing that there is an alternative.

There is always alternative,  BUT  they are NOT doing anything except  fill the hole with sand, which is a bad engineering decision without properly compaction  by any method of compaction. this is typical thai engineering  short cut rather have the money in my pocket, people wonder why roads collapse, buildings fall down, if they took pride in the workmanship and stop corruption this would not happen, this whole mess  reflects very badly on thai engineering and workmanship   

UPDATE
Stone Pouring Starts in Vajira Hospital Sinkhole Repair