Research carried out at Sheffield University has shed new light on the effects of underground blasts from landmines and improvised explosive devices (IEDs).
Using the university’s unique Explosives Arena, a team led by senior geotechnical engineering lecturer Dr Sam Clarke carried out around 250 test explosions using different soil samples. While much of the previous work in this area has focused on desert conditions – often considered to be a worst-case scenario in terms of pressure loading and fragmentation – this new study looked primarily at clay soil.
“The AEP-55 standard [used in most investigations] mandates the use of sandy gravel in soil based tests. That’s a particularly severe case for dismounted troops and local perforations of thin-walled armour, but what we’ve come to understand is that it might not be the worst total impulse scenario,” said Dr Clarke. “As you increase moisture content in the soil, the pressure distribution becomes more like a discrete wave, maintaining a higher pressure as it propagates outwards; drier soils tend to result in a more uniform temporal loading that decays more rapidly.”
The tests used a series of 17 Hopkinson pressure bars arranged on a flat steel plate 150mm above the surface of a clay test pit. Experimental data from the blasts was backed up by a numerical model developed and applied as part of a study supported by the Engineering and Physical Sciences Research Council (EPSRC). This will be fed into a wider investigation into the effects of IEDs and landmines on armoured vehicles carried out by the Defence Science and Technology Laboratory (DSTL).
“Through better understanding of how these devices behave with the soil we hope to be able to improve protection against them without increasing weight or cost,” said Dr Clarke. “It becomes increasingly relevant if you consider new materials. Hard targets such as steel may be less sensitive to the distribution of the loading, because you know they’re not going to perforate, so it becomes a total impulse problem. But if you’re dealing with a lightweight composite structure where localised failure might be an issue then you really do need to know the discretisation of the pressure over the structure as a whole.”
Its some years since I was directly involved but I do recall that one of the problems encountered by the Army in various places where IEDs were being utilized by ‘them’ was that the drivers of many vehicles insisted (because it was hot), notwithstanding their strict instructions, in driving with side-windows open! The Taliban and others quickly recognised this and ‘aimed’ their IEDs appropriately. We came-up with the concept of linking air-bag (immediate deployment) technology with that of chain-saw protection fabrics (obligatory for forestry workers) . As I have said many times: someone, somewere (often in a completely un-related industry) has considered a solution to most problems: spread the net (sorry about such a pun!) of potential solutions widely.!
What I proposed many years ago, and the USAF Research later tested and discovered, spraying the inside wall of a vehicle (or even cinderblock wall) with polyurea (truck bed liner) dramatically reduces blast effect.
Valuable idea. Many (over 30 years ago) whilst travelling by train to Budapest, at one point inside Hungary my train was stopped. At a level-crossing there was a Soviet tank (later T34 type?) on its side -clearly having been previously hit by a train! The turret was ‘off’ and the Warsaw Pact equivalent of REME were trying to right it. They were using shear-legs and a block-and-tackle to do so. I did notice that the inside of the turret was painted white: and had always thought that this was to try to accustom the crew to the potential for the ‘very bright light’ burst that was one route to blinding them? in action. Perhaps others had noted Randy’s concept. I am aware that V-bomber crews were issued with pirate style eye-patches (so that at least one of their eyes would be working after the explosion.)