I have been asking myself this question for many years after reading the comic, "Henry's Diary", which focusses on the life of british soldiers in the trenches in West-Flanders, Belgium.
At a certain moment the squadron is hiding in a bunker for several days, while the entire area was being bombed to shreds. As this must have been extremely nerve-wrecking, I wonder what the effects of a (non chemical) direct hit would bring.
Of course, this would depend on the type of bunker, or on the material it was built in.
Would it be more likely to die due to the explosion? Collapsing of the walls?
A couple of points here. The British tended not to build concrete bunker in their forward trenches - too difficult to do that close to the enemy. So if they were in a concrete bunker, they were probably in the rear, support area. Forward bunkers were re-inforced with logs, wood, sandbags and the like. A key factor is what was the caliber of the artillery that was shelling them? The smaller the caliber, the less likely to penetrate the bunker. A direct hit with a smaller caliber would likely cause 'spalling' - where the interior lining of the bunker would be blown into the bunker by the shock of the explosion. If the bunker was lined with concrete, then the occupants would be covered/hit with bits of concrete. A large caliber shell would probably result in the bunker collapsing on the occupants. A key to the above is what type of fuse the artillery shell had. A 'PD' - point detonating would explode on contact with the ground. A 'TD' - time delay, would penetrate X number of feet before exploding. This information is based on my 21 years as a US Army Officer, although I have read extensively on this subject in WWI. The Battle of Verdun is a great example of the effects of Artillery on fortified bunkers.