DEMICHAIN: A New Concept of Mechanical Demining

by René Joecklé [ Association de Recherche de Techniques Innovantes en Déminage humanitaire ]

DEMICHAIN is a new concept for mechanical demining, in which a horizontal web of heavy chains hung several metres above a surface to be cleared is dropped in a free fall and delivers a mechanical impulse over the whole surface hit by the chains. A pressure wave expands in the soil and is expected to trigger the active landmines. A description of the device is given, as well as comparisons to other demining devices. The author offers that DEMICHAIN provides numerous advantages to current mechanical-demining techniques, though it requires further testing before it can be used in real-life situations.

Most mechanical-demining devices, such as flails and tillers, penetrate soil to a certain depth and can trigger or demolish the explosive devices encountered. A lot of energy and specialized tools and devices are needed for this task. Triggering the explosion of an active landmine, however, is an alternative method. Rollers work in this way, but the required pressure makes it necessary to have heavy rollers and large engine power to drive them.

A drawback of these mechanical devices results from the fast decrease of stress generated with depth.1 A landmine with a small pressure plate can therefore remain dangerous if deeply buried. In order to remedy this problem, ARTID proposes the DEMICHAIN.2 This tool is not yet in use in minefields, and careful tests are needed before using it on mine-affected ground. Yet its potential advantages warrant a study of its expected effectiveness.

Description of DEMICHAIN

DEMICHAIN means "DEMIning with CHAINs". Jacques Demichelis invented this idea and developed it within the framework of ARTID.3

Still in the testing phase of development, the DEMICHAIN consists of a horizontal web of heavy chains hung several metres above the ground, which, when dropped in a free fall, delivers a mechanical impulse over the ground hit by the chains. A pressure wave is generated in the soil, which triggers active landmines. A large area is simultaneously under stress and the resulting forces decrease slowly with depth, in contrast with other mechanical-clearance devices.

Figure 1: Principle of DEMICHAIN. All Graphic Courtesy to the Author.

The main characteristic of this demining method, as compared to rollers and flails, is that the forces are vertical and uniformly distributed over a large surface. The dimensions of this area are more than 10 times larger than the normal clearance depth requirement of 20 centimetres (8 inches). It is assumed, therefore, that the phenomenon is one-dimensional (i.e., the stress variation is significant only in the direction of the depth).

A theoretical description can be made4, assuming the soil is elastic and is hit by a uniformly distributed mass with a velocity Vo of about 8 metres per second. After a few microseconds, it can be assumed that the surface of the soil moves with a velocity of Vo and is compressed. This elastic strain generates a vertical stress and results in a pressure wave, which expands at the velocity of sound. The theoretical value of this stress, S0, on the surface at the very beginning of the impact is given by the Timoshenko expression:

S0 = r c V0

where r is the mass density and c is the velocity of sound in the soil. This latter variable varies strongly with the water content of the soil—between 160 and 1000 metres/second (525 to 3,280 feet/second). Even with the lowest value, the stress for an initial velocity of about 8 m/s generates a vertical pressure (4.106 Pa) that is higher than the pressure that triggers a landmine.

Table 1: Triggering pressure of several anti-personnel landmines.

Other theoretical considerations yield the following conclusions:


Figure 2: The four phases of a cycle.

How Will DEMICHAIN Work?

The demining process occurs during a fraction of second over an area of several square metres; however, it must be followed by a change in the positioning of the chain web. This is completed in a cycle of three to four phases:

  1. The chain web is released and falls freely, whereupon it impacts the ground and detonates all the active mines present.
  2. The crane or hydraulic arm recovers the chain web.
  3. The chain web is lifted to the required height.
  4. The DEMICHAIN is moved to the next demining location.5

Figure 3: A succession of cycles.

The demining operation consists of a succession of cycles, either in front of the machine, as for flails and rollers, or by covering a broader zone through a combination of linear movement and rotation of the crane.

For safety, the surface must be impacted several times. Movement of the DEMICHAIN must therefore be adjusted as a function of this requirement and the dimensions of the chain web.

Two types of lifting devices can be used:

Comparison with Other Mechanical Demining Machines

DEMICHAIN affords several advantages over flail and roller machines. The chains are vertical and can work on uneven ground. Ground obstructed by stones, small rocks, banks, ditches, small fences or barbed wire, for instance, cannot be cleared by flails or rollers but could be demined with DEMICHAIN. In addition, the chain web is cheap and rugged and could be built locally. Its geometry could be adapted to the place to be demined, for instance a road or a trail, with ditches and banks. It is a tool that could be fitted to many lifting machines. This concept is within the reach of demining organisations that cannot afford specialised machines. It is also well adapted to dealing with problems such as small areas or uneven parts of large areas.

ARTID's Study

Methodology. DEMICHAIN, being a new concept, must be well understood before being used on live areas. Taking advantage of the characteristics of DEMICHAIN (one-dimensional effect), ARTID is performing a study of the forces developed by the free fall of a web of chains on buried force detectors.

Prototypes. So far, ARTID has built two prototypes:

Figure 4: The "light" device.
Figure 5: The "heavy" device.

Force measurement. Rugged detectors have been built in which springs are compressed as a piston moves and closes a micro-switch as soon as the force exerted on the pressure plate exceeds 15 kilogram-force (150 Newtons). The diameter of the pressure plate ranges from 4 to 9 centimetres (1.5 to 3.5 inches). An electronic unit collects data from up to 10 detectors and records the transient signals from the micro-switches. These detectors are generally buried at depths of about 20 centimetres (8 inches).

Results. Results have been obtained, showing that the detectors buried 20 centimetres (8 inches) deep react positively to both prototypes with a free fall height of more than 2.5 metres (8 feet). Different soils have been tested: agricultural soil (meadow), gravel, sand, and sandy soil (rubble). This last soil type was very dry and firm, whereas the others were waterlogged. No differences of behaviour have been observed. One test, with detectors buried 45 centimetres (18 inches) deep in sandy soil, was also positive with a height of free-fall of 3 metres (10 feet).6

A further test was made by putting stones that were more than 10 centimetres (4 inches) in diameter among the buried detectors. Most of the detectors reacted positively. Those that did not were located at the edge of the impacted zone. A careful investigation of the useful area will be made because the propagation of the pressure wave at the edge is no longer one-dimensional.

Where Could This Tool be Useful?

The deminer's toolbox can be completed by adding to it a DEMICHAIN for dealing with following problems:

Another potentially interesting application, which has not yet been completely investigated, is the ability to generate the required forces at great depths. This is an interesting feature for sandy areas like deserts, where the burial depth can vary due to the movement of the sand. Moreover, there is no wearing down on the chains by the sand as there is with flails.

Conclusions: Tests with Real Landmines

As soon as the current study is completed, tests on real landmines will be required before the device can be used on minefields. Testing can be performed, for instance, at the CTRO in Croatia, which seems to be specially adapted for such tests. The problem today is to obtain the necessary funding. Etablissement Technique de Bourges in France has shown an interest recently in testing the DEMICHAIN.

ARTID's mission is to perform research into new ways to help eradicate anti-personnel mines. We encourage other organisations to review our results and develop, test and use the DEMICHAIN in order to eradicate AP mines faster. The DEMICHAIN concept and the results of the study are published at http://www.artid.org and the concept is not patented. Bullet

The author would like to thank all the members of the ARTID who helped in the testing and who were party to the fruitful discussions, namely Christian Baras for the electronics; John Crawford for a good English translation; Robert Goepfert for work with the "light" prototype in Ranspach-le-Bas; Claude Hartmann for building the prototypes; and Bernard Gautier, Jean-Pierre Hancy, and Danielle and Michel Samirant for their participation in the tests. The author is also especially thankful to Jacques Demichelis for his idea and interesting suggestions.

Biography

Dr. René Joecklé is retired. He was previously employed as a Senior Scientist at the French-German Research Institute of Saint-Louis (ISL—France). Involved in laser-material interaction studies, he dealt with novel military demining techniques. He is a founding member of ARTID, an association for developing new tools for humanitarian demining, and he serves as its president.

Endnotes

  1. Shankhla, V.S. "Unravelling flail-buried mine interaction in mine neutralization." Technical Memorandum DRES TM 2000-054 (December 2000).
  2. Joecklé, René. "Research of new tools for demining by ARTID." p. 680, EUDEM2 — SCOTT Conference, Brussels, September 2003.
  3. ARTID: Association de Recherche de Techniques Innovantes en Déminage humanitaire is a French association, set up in 2000 to find and develop new techniques for humanitarian demining. Most of its members are retired scientists or engineers. It is located in Saint-Louis, a small French city at the junction of the borders between France, Germany and Switzerland. One of its tasks is gathering and diffusing information about demining techniques. http://www.artid.org. Accessed 27 February 08.
  4. Pearce, R.W. & Scott, R.A. "Soil compaction by impact." Institution of Civil Engineers: Symposium Report, 1976.
  5. On almost all the mechanical demining techniques (flails, rollers, tillers), the vehicle drives on the ground which has been previously cleared by one method. Normally, the survivability of this vehicle in case of an accidental explosion has to be tested. A second method has to be applied then in order to be sure to get a mine-free ground.
  6. The DEMICHAIN concept is new and different from the others methods of mechanical demining. Since the aim of this paper is to simply present the concept, a detailed description of the tests performed up to now has not been provided by the author. To discuss the specifics, contact the author.
  7. Maquis is "a dense growth of small trees and shrubs in the Mediterranean area."

Contact Information

René Joecklé
President
ARTID
8 rue des Roses
F — 68300 — Saint-Louis / France
Tel: +33 369 444 259
E-mail: association@artid.org
Web site: http://www.artid.org/