Sensitivity analysis of a scrap tire embankment using Bayesian influence diagrams

Scrap tires have several properties that make them preferable to other materials as fills for embankment construction, including light weight (the dry unit weight is 1/3 that of soils), high hydraulic conductivity (up to 23.5 cm/s), and low thermal conductivity. These properties of scrap tire fills result in low lateral pressures on the abutment wall and in reduced design and construction costs. The low thermal conductivity helps to prevent permafrost action of soil layers beneath it and failure of the subgrade due to frost penetration. However, scrap tires possess high compressibility, a property that leads to settlement of the fill and consequent failure of the embankment. Other undesirable attributes of scrap tire embankments are susceptibility to internal heating and leaching of substances into surrounding water. An efficient means of controlling such undesirable attributes in the field is by comparing them with those simulated from a model embankment developed using Bayesian influence diagrams. In this work, the essential responses simulated using the Analytica (R) software program are the temperature, lateral pressure, settlements, and leachate characteristics. The most critical embankment characteristics, based on the maximum probability densities, are the settlement and horizontal pressures, which are relatively low at 0.428 and 0.0034, respectively, because the likelihood that these values will be exceeded in the field is high. Temperature response was not considered critical because the maximum probability density simulated was 0.9301. Limits for leachate concentrations were also obtained for the model embankment based on ASTM D 6270 (1998) standards. (C) 2008 Elsevier Ltd. All rights reserved.