Development of a Procedure for the Structural Evaluation of Superheavy Load Routes (1335-3F)

The Texas Department of Transportation (TXDOT) receives about 75 to 100 permit requests for superheavy load moves annually. Most of the moves take place in the southeast region of the state due to the proximity to the Gulf of Mexico and the presence of navigational inland waterways. Gross vehicle weights associated with these moves range from 1112 kN to over 8896 kN and include loads like dragline components, off-shore pipe-laying equipment, oil pressure veseels, and electric transformers. The number of superheavy load permit applications has increased over the years. Before a permit can be issued, TxDOT needs to determine whether the proposed route is structurally adequate to sustain the superheavy load. The analysis of damage potential under superheavy loads concerns the likelihood of a rapid, load-induced shear failure as opposed to the long-term accumulation of permanent deformation and fatigue due to repeated load applications. In this project, researchers developed a procedure for evaluating the potential for pavement damage prior to a superheavy load move based on the Mohr-Coulomb yield criterion. In developing this procedure, researchers investigated the sensitivity of the Mohr-Coulomb yield criterion to changes in the predicted stress state and material strength parameters; compared different models for evaluating pavement response under vehicle loading; and investigated the effect of different load configurations on the predicted pavement response and yield function value. Using the results from these investigations, researchers developed a two-stage procedure for the structural assessment of superheavy load routes which utilizes existing capabilities within TxDOT. Flexibility is provided to conduct structural evaluations with varying degrees of complexity depending on the quantity and quality of information available on the proposed superheavy load route. In the first stage, structural adequacy is evaluated by means of charts with minimal requirements for materials characterization. Relationships are provided for estimating resilient and strength parameters of base and subgrade materials from results of simple soil tests. Should the initial results indicate that the structure is inadequate to accommodate the expected superheavy load, then the second stage analysis should be conducted which requires a more detailed characterization of the proposed route. In this stage, the evaluation uses an incremental non-linear layered elastic computer program. This report documents the development of the methodology for permitting superheavy load moves.