IMPLEMENTATION OF FALLING WEIGHT DEFLECTOMETER LOAD-ZONING PROCEDURE IN TEXAS

The Texas Transportation Institute, on behalf of the Texas Department of Transportation (TxDOT), has developed a computer program, LOADRATE (Project 473) to be used as a load-zoning analysis tool for two-layer pavements. A comparison study was undertaken of the solutions generated by LOADRATE and those obtained using the Texas triaxial classification methodology for determining allowable wheel load capacity. The Texas triaxial method historically has been used to determine whether load zoning is warranted on a given roadway and is also used as a "check" for pavement designs generated by the flexible pavement design system computer program when used for low-traffic-volume roadways. For this comparison, deflection data were collected on all load-zoned roads (228.68 mi) in Ellis County of the Dallas district using the falling weight deflectometer. The LOADRATE program was used to compute both unadjusted and adjusted base moduli using the temperature/moisture correction features of the LOADRATE program. An allowable axle load for single, tandem, and tridem axles was then computed by the program using an allowable rut depth of 0.5 in. as the failure criteria. The results generated by the LOADRATE program do not give reasonable allowable loads as a function of pavement thickness. Additional field calibration of the LOADRATE program is warranted.