Elsevier

Journal of Terramechanics

Volume 40, Issue 4, October 2003, Pages 271-283
Journal of Terramechanics

Soil stress distribution related to neutralizing antipersonnel landmines from human locomotion and impact mechanisms

https://doi.org/10.1016/j.jterra.2003.12.006Get rights and content

Abstract

Soil stress distribution was investigated to understand and to develop means for detonating or neutralizing antipersonnel landmines. Specifically, the loading patterns within the soil attributable to the human gait, as well as those derived from a mechanism that delivers an impact load that is being developed for neutralizing antipersonnel landmines, were studied. Experiments were conducted in the soil bin facilities in the Department of Agricultural and Bioresource Engineering at the University of Saskatchewan. Both load cells and mechanically reproduced devices (MRDs), buried at depths of 50, 100, 150 and 200 mm, were used to measure the transmitted forces through the soil. The load cells provided measurements of the temporal load patterns as transferred through the soil, whereas the MRDs indicated the ability for the person or mechanism to successfully trigger a typical antipersonnel landmine. Both forces and impulses based on the load cell data were used as measures for comparison. The key results of the investigation showed human locomotion imparted a load of longer duration than did the impact from the mechanical device; the corresponding soil stresses increased with increasing human weight and impact loads; and forces in the soil increased with higher initial soil compaction level.

Introduction

Landmines are weapons of mass destruction in slow motion. Nearly one hundred million uncleared landmines lie in fields and along roads and footpaths of one-third of the countries in the developing world. During the past 25 years, more than 50 countries have manufactured about 200 million antipersonnel landmines. Daily, an estimated 70 people are killed or injured by antipersonnel mines. According to the United Nations, the clearance costs for one landmine is approximately US $1000. The current, acceptable mine clearing and neutralization practices use manual methods that are slow, labor intensive, high risk, and expensive. Although several machines have been developed, they have had limited success, as they generally require very large power units, which are very costly. Therefore, new mechanical systems are needed that will be simple, efficient, and economical to expedite the clearing process and reduce the risk associated with the neutralization of buried, pressure-activated landmines.

The transfer of the technology of soil dynamics and stress distribution to this area has been limited. Therefore, the development of mechanisms for mine clearing has relied on trial and error and intuition, rather than sound technical judgment. Often, existing agricultural, road and heavy construction and forestry equipment is used as is or with slight modifications. The results have been expensive and inadequate in meeting the needs of the international demining community.

To effectively neutralize landmines, an understanding of the load transfer through the soil is required. The stress distribution associated with loading both from the human gait and from a mechanism designed to neutralize antipersonnel landmines is studied. Because the interaction is time dependent, a dynamic load approach was taken. Theoretically, a common method to estimate stress in soil is a Boussinesq solution based on the assumption that soil always reacts elastically [1]. Although soil is non-elastic, non-homogeneous, and non-isotropic, the research on stress distribution in soil indicates that the classical Boussinesq solution, when properly applied, provides a reasonably good guide for predicting the stresses in the soil [2]. Sharifat and Kushwaha [3] used the Boussinesq solution with an equivalent impact load to estimate the stress in soil from impact loading. The results, when validated experimentally, showed that the Boussinesq solution underestimated the stresses in soil. Rubinstein and Wolf [4] used a basic model of a single chain impacting the soil and applied the Hertz contact theory to determine ground-surface-level impact forces. The soil was modeled as a linear elastic material, which is a simple representation of the soil. They developed model for estimating the ground-surface-level impact forces that can be used to optimize the design of a demining device. However, further study was recommended to determine the impact force applied directly to the mines.

The intention of this study was to understand the physics of the soil to develop a more efficient and effective mechanism for antipersonnel demining. This study examined the load distribution in soil associated with the human gait and with the impact loading mechanism in different soil conditions. The effects of impact loads on the soil stress distribution associated with variations to the mechanism (namely, varying operating conditions and design components) and with different soil conditions were investigated.

There are two general types of landmines: antipersonnel (AP) (Fig. 1) and antitank (AT) (Fig. 2). Both types of mines are similar having activation and pressure plates, a detonator, and a charge of explosive. The anti-tank landmine may contain 10 kg of explosives while antipersonnel landmine typically contains about 100 g of explosive. It is estimated that the ratio of antitank to antipersonnel landmines is 1:1000 [5].

Antitank landmines are designed to disable or destroy vehicles. The M-15 antitank landmine, manufactured in the US, requires between 1.5 and 2.0 kN of force for activation while antipersonnel landmines requires much lower force for detonation. The M-14 antipersonnel landmine requires between 88 and 157 N of force, while the PMA-1 requires 29 N of force [5].

Section snippets

Materials and methods

The experiments were conducted in the soil bin facilities at the University of Saskatchewan, Saskatoon, Canada. The soil bin is 1.75 m wide, 0.3 m deep and 12.2 m long (Fig. 3). The soil bin carriage is propelled by a variable speed electric motor and its speed can be varied between 0.9 and 8.5 km/h.

Neutralization mechanism

The impact of the hammer striking the ground imparts a force (F) to the soil that has both a normal (Fy) and tangential (Fx) component (Fig. 5). The normal component (Fy) as measured by the load cells has been reported as the transferred load.

Several replicates were conducted with consistent results being obtained. A typical output from the load cell illustrating the impacts of the passing rotary mechanism is shown in Fig. 7. These results were obtained for a load cell buried 150 mm deep and in

Conclusions

The distribution of impact loadings from the mechanical device and from the human gait trials under various degrees of soil compaction were measured. Although the impact profiles were significantly different between the human gait and the mechanical device, the generated impulses were very comparable. The duration of the impact load transferred by the human gait ranged between 500 and 800 ms, whereas each hammer strike only transferred load for 10–20 ms. The distance between consecutive load

Acknowledgments

The authors gratefully acknowledge the financial assistance received from the Natural Sciences and Engineering Research Council (NSERC) Canada and the Defence Research and Development Canada (DRDC), Suffield, Alta., Canada. Also, the research efforts of post-doctoral candidate, Karim Sharifat, in conducting the preliminary investigations were gratefully appreciated.

References (8)

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