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88 • <br />conditions will perform satisfactor- <br />ily for either a lesser speed or a <br />shallower impact angle. Since a loaded <br />vehicle would impose the more stringent <br />strength requirements on the berm, only <br />the responses of loaded vehicles were <br />evaluated. <br />GEOMETRIC-SCALE MODEL SIMULATIONS <br />Scale models of haulage trucks, edge- <br />of-road berms, median berms, and escape <br />lanes were constructed to provide corre- <br />lation between field tests and computer <br />simulation. The 35-, 85-, and 170-ton <br />haulage trucks were selected as being a <br />representative cross section of the haul- <br />age vehicle population. Using simili- <br />tude, 1/20-scale model haulage Crucks <br />were constructed Eor each size truck. <br />The primary parameters of interest were <br />the mass moments of inertia about the <br />roll, pitch, and yaw axes. These inertia <br />values were not available from the truck <br />manufacturers and therefore were deter- <br />mined experimentally since they were <br />essential for determining the proper dis- <br />tribution of mass during model construc- <br />tion. The model trucks were fabricated <br />using these data and truck manufacturer <br />data. <br />For truck modeling purposes, small <br />double-acting cylinders simulated the <br />commonly used nitrogen-over-oil sus- <br />pension. For practical purposes, rigid <br />rather than pneumatic tires were used on <br />the model. A locked steering system was <br />used to represent vehicles without <br />steering-turn self-correction. No at- <br />tempt was made to model body strength. <br />Ground clearances and general configura- <br />tion of the haulage truck were modeled. <br />Vehicle weight distribution, sprung and <br />unsprung masses, and suspension charac- <br />teristics were scaled from values ob- <br />tained from various manufacturers. <br />Berm composition is different at every <br />mine. To simulate the spectrum of possi- <br />ble berm compositions, scaled unconsoli- <br />dated and rigid berms were investigated. <br /> <br />The unconsolidated berm was represented <br />by a loose deposit of soil uniformly dis- <br />tributed to a specific height. Compacted <br />clay material was used to represent a <br />rigid berm. Model tests were also run at <br />intermediate berm strengths. <br />FULL-SCALE FIELD TESTS <br />Field tests of haul road berms were con- <br />ducted using a 35-ton haul truck. The <br />relative ability of this material to re- <br />strain a 35-ton haul truck under varying <br />approach conditions, berm heights, and <br />compaction conditions was tested. Data <br />collected included tire sinkage, wheel <br />climb, and penetration along the direc- <br />tion of travel (fig. 1). Economic con- <br />straints of the field test program pro- <br />hibited testing that would result in <br />damage to [he vehicle. As a result, <br />small approach velocities were tested at <br />various approach angles and then in- <br />creased to the point where safety of the <br />test was questionable. Yesults of the <br />field test did not provide the informa- <br />tion needed to predict the approach con- <br />ditions at which rollover will occur. <br />The field test information is, however, <br />the basis for determining the correlation <br />between the computer simulations and the <br />scale model simulations. <br />COMPUTER SIMULATIONS <br />Computer simulations of vehicles in- <br />teracting with edge-of-road berms were <br />performed using a highway-vehicle- <br />object-simulation model (HVOSM).5 This <br />program predicts the response of a <br />vehicle and the forces generated during <br />the vehicle's interaction with a rigid <br />nondeflecting surface as a function <br />of vehicle impact speed and approach <br />angle. <br />SSegal, D. J. Highway-Vehicle-Object- <br />Simulation Model--1476. Vol. 4, EnS=- <br />neering Manual--Validation. CalcFan <br />Corp., Buffalo, NY, Report FHWA-RP-~~ <br />165, Feb. 1976, 460 pp. <br />i <br />I <br />i <br /> <br />al <br />