Spatial Mapping of Soluble Sulfate Concentrations Present in Natural Soils Using Geostatistics

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Sulfate heaving has had a major impact on civil engineering infrastructure for the past few decades. Past researchers have attributed the provenance of this heaving mechanism to the chemical reactions between soluble sulfates and calcium-based stabilizers, but despite the increase in studies related to sulfate heaving, very little effort has been made to address the variability of sulfate concentrations in the field. The natural deposition of sulfate pockets causes inevitable problems to chemical stabilization techniques. Because of the high variability of sulfate concentrations present in nearby locations, it is possible that engineers may mischaracterize the sulfate concentrations or not able to design appropriate stabilization measures in the field. In this study geostatistical analysis was used to quantify and map sulfate concentrations along a mega water pipeline project located in north Texas. Various soil samples, originating from six different geological formations along the pipeline alignment, were collected. Laboratory tests were performed on these soil samples to determine soluble sulfate concentrations using the modified University of Texas at Arlington (UTA) approach. The inherent variability present in sulfate concentrations was determined and modeled using variogram analysis. The variability models, along with the kriging algorithm, were used to determine the distribution of the sulfate concentrations at unsampled locations along the pipeline alignment. This analysis provided the distribution of soluble sulfate concentrations along the six geological formations and indicated the areas of having low-risk to high risk zones when treated with calcium-based stabilizers. This research highlights the adoptability of geostatistics in modeling and mapping the high variable soluble sulfate concentrations present in native clayey soils.