Understanding the Role of Soil in Subsurface Explosive Events

Deaths and injuries from the effects of land-mines are common results of both active war-zones and post-conflict legacies. Aside from the regular headline-making news when UK armed forces are attacked by IEDs, it has been calculated that some 110 million land-mines are left in post-conflict zones, leading to the death of around 800 people per month and the maiming of many others.

Development of protective clothing and footwear, vehicle design and retrofitting systems and efficient mine clearance systems for both active defence and civilian mine-clearance operatives, depends on the accurate assessment of the blast loading produced by the detonation of a shallow-buried explosive. This is a highly complex detonation event, involving the interaction of extremely high-energy shock waves with multiple materials in different phases (soil, air and water).

This project aims to develop a deep understanding of how the soil surrounding buried explosives affects the resulting detonation and to develop advanced soil models which describe this behaviour. With a newly applied methodology this project aims to test clays with a high degree of accuracy to develop a dataset that will complement an existing equivalent data for sands and gravels. This will allow a direct comparison between the two soil types to assess the main contributing factors to the blast created during the tests.

It has been postulated by other researchers that the resulting impulse given out by a shallow buried explosive is inversely proportional to the shear strength of the soil in which the explosive is buried. This hypothesis is to be tested by developing a new high pressure, high strain rate testing apparatus to shear soils in similar conditions to those experienced in explosive events. This novel apparatus will for the first time be able to investigate the fundamental shear properties of compressible materials.

The understanding gained from this project will provide a revolutionary dataset for the modelling of soil-explosive interaction events and lead to developments in protective solutions for both civilian and defence applications.

The project will provide for the first time a reliable, and tightly controlled dataset of impulse measurements from explosives buried in clays. This will be of great value to the defence community who currently provide advice for troops in conflict areas in regard to route planning and risk assessment. The knowledge gained during this project will greatly help in this process.

The newly applied methodology for the creating of repeatable clay samples will help raise the standard of physical blast testing conducted around the world. This will allow the creation of accurate advanced constitutive models to describe the soils in extreme loading regimes. This in turn will mean that numerical simulations developed to use such models will be more reliable and critically, be able to simulate realistic events.

The advanced high strain rate shear failure data generated by the novel split Hopkinson pressure bar containment will provide a new insight into the mechanisms and soil parameters which govern the behaviour of soil during explosive events. This will be very beneficial to numerical modellers who are attempting to simulate these events, and in doing so also the resulting effects on protective systems. This will help inform the design of new protective solutions being developed for both civilian and military applications.

The methodology used to determine the shear failure of the soils at high rates will also be applicable to other advanced materials whose shear strength are dependent on confining pressure. These materials include advanced composites and other porous media.