Against dug-in troops skulking in their holes, do rounds pretty much have to land in the trench/foxhole to cause casualties? I can't understand how being in the dirt only a few meters from a 155 or 120mm mortar round would help you much, but Soviet statistics on number of rounds required for troops dug-in the open are really high.

Is dirt/earth just particularly good at absorbing shrapnel and explosive force?

but when a test rocket explodes, you are supposed to flatten yourself, if you are caught in the open, with your feet toward and head away from, face down, mouth open and with your arms and hands over your head, to deal with the shock wave and the fragmentation of the explosion, most of which should hopefully pass over you. A trench or a hole should be much better as it gives you lateral cover from the fragmentation, but no overhead protection, so what rains down on you rains down.

 

I don't know what protection from the overpressure of a close bursting explosion you can devise except what I offered. AFAIK, if the overpressure wave is severe enough, nothing will save you from that pressure wave shock effect on you, if you are not in a protected structure or blast shelter of some kind..(tank for example).   

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The short answer is "yes'

 

Most impact fuzes, even the best and quickest acting mean the shell penetrates the dirt to some extent, although hardness and softness is a factor, as is the terminal velocity, and modern shells from modern guns generally have greater terminal velocity than those of 50 years ago.

 

Next point is that the direction of fragments is a vector sum of the terminal velocity carrying everything forward and the explosive charge, mediated by shell body shape, sending the fragments outwards.  This means that lots go forwards into ground no matter how little the shell has penetrated before exploding.

 

Fragments are very irregular in shape and retarded quite quickly in air, in dirt they ain't going anywhere more than inches.

 

Forget blast effects from artillery shells, in open ground they're negligible.  Inside a building its a differnt matter.

 

Arty fire agaisnt defensive positions is not about causing casualties (at least in smart armies that learned the lessons of WW1).  Its about neutralisation or suppression as it is now usually called.  That said Soviet norms were probably going for neutralisation that they interpreted as about 15% casualties.

 

Of course these days with multi-option fuzes its a non issue because all HE is fuzed for various forms of ground and airburst, its just a matter of selecting which to use.  The latest Junghans fuze is a good example for HE - impact (instantaneous or delay), time (set a clock), proximity (select height of burst option), tree canopy penetration (select how far through the canopy)

 

In the case on entrenchments the effectivness of surface detonation goes way down.  The general guide we used was a 105mm HE had to hit within one meter to collapse a trench wall, & a 155mm within two meters.  To reach the 15% casualties goal in the Soviet norms it going to take a lot of metal .