Even if I were to accept the dubious premise that there is enough fractured rock to make a difference and there is no hampering with rocks falling into the void and that it's possible to hit the exact same spot repeatedly without touching the sides, all that would do in big O notation would be increase the constant factor. It would not be super linear after the second bomb.
If your are talking about bombs that hit side by side then clearly that is sub-linear as no matter how fractured the rock it’s not easier to push through than air.
An explosion creates a pressure wave. A pressure wave fractures rock. Fractured rock may be easier to pierce than solid rock.
Ergo, if first bunker buster penetrates to maximum depth -20m and then explodes, fracturing rock within a __ radius, then second bunker buster travels through that fractured rock, the second (and so on) may be able to penetrate deeper.
I have no idea about the physics of penetrating fractured vs non-fractured rock, but it's a physically plausible mechanism.
Furthermore, given the multi-minute timeline reported, there's enough time for the bombs to be deployed sequentially.
In the linear case a bomb twice the size goes twice as deep.
Take a bomb, cut it in half and drop each half separately, one after another into the same hole, would you except the cumulative depth to be greater than the whole bomb or less? Consider that in the case of the whole bomb it is equivalent to two halves arriving at the exact same time.
The strike may have been able to achieve greater penetration depth with multiple sequential weapons impacting the same point (i.e. the three seen in satellite imagery).
I'm confident that 'drilling' with multiple bombs was the known approach prior to the attack. The planned approach to soviet bunkers was to use repeated accurate strikes of nuclear bombs to achieve a similar drilling for their bunkers.
There appears to be an assumption that the main facility was exposed to blasts from the tunnels and since that appears to be an obvious weakness I'm wondering why the Iranians wouldn't have blast doors between the tunnels and the facility as a form of redundancy. I am still worried that this is part of an approach to slowly warm Americans up to another war, much easier to sell a limit strike as a success, then 3-6 months later when the Iranians have recovered it'll be even easier to sell another strike or a more involved engagement.
> Does the type of soil or rock compact or loosen when bombed?
Is the most relevant question.
It seems reasonable that fractured rock may be easier for subsequent bombs to penetrate.