E. Alex Baylot, George L. Mason, John G. Green, Ernest S. Berney IV
Predicting the stability of low volume road embankments in contingency areas
Journal of Terramechanics, Available online 10 February 2012, ISSN 0022-4898, 10.1016/j.jterra.2012.01.002.
Abstract: The US Army often operates heavy vehicles in rural areas, operating on low-volume roads having limited load carrying capacity. Many of these roads, such as the ones on the outskirts of Baghdad, have been raised to prevent flooding from nearby canals or irrigated fields. Sections of the roads have collapsed under the weight of armored vehicles, resulting in injuries and even fatalities. For the selected area studied, 2½% of the low-volume road sections were determined to be high risk given typical wheel loads of heavy vehicles for soil strength conditions modeled as low. The goal of the research was to develop a method for rapidly evaluating the stability of a road based on soil conditions, wheel load, and the dimensions of a vehicle. A model for road stability was developed to assist in performing analysis of the canal roads outside of Baghdad. This analysis was then used to create maps and charts characterizing road stability to assist the drivers. The procedure described in this paper can be used to evaluate elevated roads in other parts of the world.
Keywords: Low volume road; Embankment; Traffic; Heavy vehicles; Trafficability; Soil strength; Stability
Predicting the performances of rigid rover wheels on extraterrestrial surfaces based on test results obtained on earth
Journal of Terramechanics, Volume 49, Issue 1, February 2012, Pages 49-61, ISSN 0022-4898, 10.1016/j.jterra.2011.11.002.
Abstract: With a growing number of nations interested in planetary exploration, research and development of extraterrestrial rovers have been intensified. The usual practice is to test the performances of rovers on soil simulants on earth, prior to their deployment to extraterrestrial bodies. It is noted that in the tests the soil simulant is subject to the earth gravity, while the terrain on the extraterrestrial surface is subject to a different gravity. Therefore, it is uncertain whether the rover/rover wheel would exhibit the same performance on the extraterrestrial surface as that obtained from tests conducted on earth. This paper describes a practical methodology that can be employed to predict the performances of rover wheels on extraterrestrial surfaces, based on test results obtained on earth. As rigid wheels are used in many extraterrestrial rovers, this study focuses on examining the effects of gravity on the sinkage and compaction resistance of rigid rover wheels. Predictions obtained using the methodology are shown to correlate reasonably well with test data.
Keywords: Compaction resistance; Extraterrestrial rovers; Gravity effects; Parabolic flights; Performance; Rover wheels; Sinkage; Soil simulants
T. Tsuji, Y. Nakagawa, N. Matsumoto, Y. Kadono, T. Takayama, T. Tanaka
3-D DEM simulation of cohesive soil-pushing behavior by bulldozer blade
Journal of Terramechanics, Volume 49, Issue 1, February 2012, Pages 37-47, ISSN 0022-4898, 10.1016/j.jterra.2011.11.003.
Abstract: A numerical simulation based on discrete element method (DEM) was conducted on the excavation and pushing processes of soil by a bulldozer blade. Soil contains water and the resistance acting on the bulldozer blade is largely influenced by the cohesive force due to liquid bridges formed among soil particles. In the present study, a cohesive bond force model proposed by Utili and Nova  was introduced in which the microscopic behavior of cohesive force was modeled analogously with macroscopic shear failure characteristics. The dependency on the magnitude of microscopic cohesive force was verified. The behavior of particles changed greatly by taking into account the cohesive bond force. The characteristic behavior of excavated soil aggregates, such as rolling motion and intermittent collapsing, were observed in front of the blade surface.
Keywords: Discrete element method; Cohesive soil; Liquid bridge; Bulldozer; Blade; Soil-blade interaction
M.A. Knuth, J.B. Johnson, M.A. Hopkins, R.J. Sullivan, J.M. Moore
Discrete element modeling of a Mars Exploration Rover wheel in granular material
Journal of Terramechanics, Volume 49, Issue 1, February 2012, Pages 27-36, ISSN 0022-4898, 10.1016/j.jterra.2011.09.003.
Abstract: Three-dimensional discrete element method (DEM) simulations were developed for the Mars Exploration Rover (MER) mission to investigate: (1) rover wheel interactions with martian regolith; and (2) regolith deformation in a geotechnical triaxial strength cell (GTSC). These DEM models were developed to improve interpretations of laboratory and in situ rover data, and can simulate complicated regolith conditions. A DEM simulation was created of a laboratory experiment that involved a MER wheel digging into lunar regolith simulant. Sinkage and torques measured in the experiment were compared with those predicted numerically using simulated particles of increasing shape complexity (spheres, ellipsoids, and poly-ellipsoids). GTSC simulations, using the same model regolith used in the MER simulations, indicate a peak friction angle of approximately 37-38° compared to internal friction angles of 36.5-37.7° determined from the wheel digging experiments. Density of the DEM regolith was 1820 kg/m3 compared to 1660 kg/m3 for the lunar simulant used in the wheel digging experiment indicating that the number of grain contacts and grain contact resistance determined bulk strength in the DEM simulations, not density. An improved correspondence of DEM and actual test regolith densities is needed to simulate the evolution of regolith properties as density changes.
Keywords: Mars Exploration Rover; Discrete element method; Triaxial test; Lunar regolith simulant
Ataur Rahman, Altab Hossain, Zahirul Alam A.H.M., Mabubur Rashid
Fuzzy knowledge-based model for prediction of traction force of an electric golf car
Journal of Terramechanics, Volume 49, Issue 1, February 2012, Pages 13-25, ISSN 0022-4898, 10.1016/j.jterra.2011.08.001.
Abstract: The methods of artificial intelligence are widely used in soft computing technology due to its remarkable prediction accuracy. However, artificial intelligent models are trained using large amount of data obtained from the operation of the off-road vehicle. In contrast, fuzzy knowledge-based models are developed by using the experience of the traction in order to maintain the vehicle traction as required with utilizing optimum power. The main goal of this paper is to describe fuzzy knowledge-based model to be practically applicable to a reasonably wide class of unknown nonlinear systems. Compared with conventional control approach, fuzzy logic approach is more efficient for nonlinear dynamic systems and embedding existing structured human knowledge into workable mathematics. The purpose of this study is to investigate the relationship between vehicle's input parameters of power supply (PI) and moisture content (MC) and output parameter of traction force (TF). Experiment has been conducted in the field to investigate the vehicle traction and the result has been compared with the developed fuzzy logic system (FLS) based on Mamdani approach. Results show that the mean relative error of actual and predicted values from the FLS model on TF is found as 7%, which is less than the acceptable limit of 10%. The goodness of fit of the prediction value from FLS is found close to 1.0 as expected and hence shows the good performance of the developed system.
Keywords: Artificial intelligent system; Traction; Fuzzy logic system
A. Benedetto, F. Tosti, L. Di Domenico
Elliptic model for prediction of deflections induced by a Light Falling Weight Deflectometer
Journal of Terramechanics, Volume 49, Issue 1, February 2012, Pages 1-12, ISSN 0022-4898, 10.1016/j.jterra.2011.10.003.
Abstract: The use of a portable lightweight deflectometer for construction quality control and road construction is increasing around the world. However there are some points of weakness that have been poorly investigated in the past. One of them is the definition of the domain of influence of the deflectometer for various test setups and different soils. This paper proposes a new model based on the Boussinesq theory that has been calibrated using the outcome of experimental tests. The series of laboratory and field scale investigations that are presented here are not conventional. In particular the actual deep deflections have been measured under the surface using an original experiments setup. Using the calibrated model, it is also suggested that a revised version of the corrected Boussinesq equation be used to better represent stress distribution in soil, where a second parameter is included along with the so called Froehlich concentration factor.
Keywords: Light Falling Weight Deflectometer; LFWD; Boussinesq model; Road pavement; Stress distribution in soil; Deflections and strains