Roadway Heaving Caused by High Organic Matter

A forensic study was conducted to investigate the premature pavement failure of heaving and cracking on the north bound lane of SH6 and to determine (1) the causes of the heaving and cracking; (2) the severity and extent of the problem; and (3) a prevention strategy. Ground penetration radar (GPR), falling weight deflectometer (FWD), dynamic cone penetrometer (DCP), and soil boring and laboratory tests were conducted. Soil maps provided by the Natural Resource Conservation Service (NRCS) and the electrical resistivity tomography (ERT) were utilized to locate areas that may have similar problems for the ongoing project. It was concluded that the heaving was caused by high organic content in soils. The low pH of the lime treated subgrade layer indicated that the lime stabilization was ineffective. This was due to the high concentration of organic matter. FWD and DCP results indicated that the heaved/cracked areas are losing structural load support. Approximately 84% of the bumps/dips detected by the profiler were also detected by the GPR. Based on the GPR results, it was estimated that about $1.2\text{miles}$ of the roadway may have potential heaving in the future. Although it is not a standard practice to determine the organic content of soil for new construction, it is critical to determine the organic matter through soil boring and laboratory testing in the suspicious areas. It was found that the soil maps provided by the NRCS yielded a reasonable estimate, and can be used as a screening tool. All five locations (O1 to O5) identified by ERT were verified by boring and laboratory tests to have high organic content (1.9–3.3%). Boring results indicated that ERT was able to map the soil strata and could differentiate between sandy and clay soil types. Although ERT was able to identify the anomalies with high organic contents, and the results were confirmed by boring and laboratory testing, additional work is needed to refine the procedure.