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Title: A study of soil disaggregation and displacement using high-pressure gas
Authors: State University of New York at Buffalo.
U.S. Army Mobility Equipment Research and Development Center.
Selig, E. T. (Ernest Theodore), 1933-
Bell, Adam C.
Keywords: Computerized simulation
Earth moving
Explosion effects
Gas explosions
REDSOD (Repetitive Explosion Device for Soil Displacement)
Soil displacements
Soil dynamics
Soil mechanics
Publisher: U.S. Army Engineer Waterways Experiment Station.
Engineer Research and Development Center (U.S.)
Abstract: Abstract: A laboratory model study and computer analysis were conducted to develop an understanding of the basic principles governing the process of earth-moving accomplished by applying a repetitive gas explosion to the soil. The results were desired for estimating the performance characteristics and design criteria for the device known as REDSOD (Repetitive Explosive Device for Soil Displacement). This study was concurrent with prototype testing being conducted at Southwest Research Institute. A small model embodying the basic features of the device was tested in cohesive and granular soils in a specially constructed soil bin. The vertical reaction plate on the front of the model in contact with the soil was 12 in. wide and contained an exhaust port along the bottom edge. In the tests, the port depth below the soil surface ranged from 2 to 8 in. A chamber in the model was filled with nitrogen to the desired pressure level simulating the high gas pressure created by combustion of a fuel-air mixture in a chamber. The model chamber volume ranged from 40 to 127 cu in. The initial nitrogen pressure ranged from 120 to 450 psi. The cohesive soil consisted of a mixture of kaolin clay and a nonvolatile plasticizer liquid to represent water. Two levels of compaction effort provided a loose and a dense clay. The cohesionless soil consisted of the same liquid and a uniform Ottawa sand. Scaling criteria were evolved and empirical equations determined from the model tests to relate the controlling parameters to the resulting soil crater volume and recoil force. A minimum pressure was observed for each port depth and soil condition, below which no crater was formed. Furthermore, a particular depth existed, for each combination of the other controlling parameters, which gave the maximum crater volume; depths both greater and less than this value produced smaller craters. The recoil force, on the other hand, continued to increase with depth. The observed model craters were similar in shape to those of the prototype. Soil appeared to fail primarily in tension rather than in shear. The rupture zone extended beyond the width and depth of the device, thus producing trenches with loose sides and loose bottom. In most tests the model remained in its original position and the soil was replaced after each shot so that it was compacted to the full depth of the port; in other tests trenching was simulated by advancing the model after each shot. The average volume per shot in continuous trenching was on the order of 1/3 to 1/6 of the corresponding single-shot volume. However, the trenching productivity was also significantly affected by the initial horizontal force with which the device was pushed against the soil to seal the ports. In loose or weak soil the vertical reaction plate could be pushed far enough to make full depth of contact with the soil. This limiting condition should produce crater volumes in trenching which are about the same as the single-shot values. For a second pass in the same trench with the port depth double that of the first pass, the trenching productivity was observed to be about half of that on the first pass, all other parameters held constant. The average recoil force in the trenching tests was about half that in the corresponding single-shot tests. The computer simulation of the REDSOD device provided a means of evaluating the effect of the system parameters on the dynamic response of the mechanical device. To accomplish this, a set of differential equations was derived for the three main components of the system: the gas blowdown process, the mechanical device,and the soil. The computer program was adapted to fit the observed dynamic characteristics of the experimental model. Then the parameters were changed to represent cases not tested in order to estimate the effect on performance. An important observation was that the shock absorber characteristics did not strongly influence the results. A comparison of estimated REDSOD productivity with that of conventional methods of earthmoving indicated that both were of the same order of magnitude. Under the most ideal conditions, with repetitive explosion rates considerably greater than achieved with the prototype to date, productivity improvement over conventional methods is not expected to reach a factor of ten. At present, conventional methods have the advantage that the excavation is more stable and the disposal of the soil removed is more controlled. NOTE: This file is very large. Allow your browser several minutes to download the file.
Description: Contract Report
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Contract Report

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