The suitability evaluation of dredged soil from reservoirs as embankment material.

We assessed the suitability of soil dredged from reservoirs as embankment material and investigated its physical and geochemical properties and strength parameters, as well as its environmental stability. The dredged soil samples were taken from the Ansung, Jechon, and Mulwang Reservoirs in Korea. To evaluate their environmental stability and geochemical properties, we examined their levels of heavy metal contamination, pH, and electrical conductivity. We also conducted X-ray fluorescence and X-ray diffraction analyses. Furthermore, we determined the geotechnical characteristics, such as the compaction characteristics, and permeability coefficient, and we performed consolidated undrained triaxial compression tests to evaluate the recycling potential of dredged soil as embankment material. The concentrations of heavy metals in the sediment samples were lower than those of the standard samples. The pH value of the soil samples ranged from 4.25 to 5.39, and the electrical conductivity ranged between 83.3 and 265.0 µS/cm, indicating suitability for use as construction material with steel and concrete. Based on the values of the mechanical properties of the dredged soil, analysis of slope stability was performed for various cases and water level conditions. Our results indicate that the dredged soil has sufficient stability for substitution of embankment material and also as new embankment material for expansion.

Recyclability of bottom ash mixed with dredged soils according to the transportation distance and mixing ratio through the estimation of CO2 emissions.

Bottom ash and dredged soils can be used as construction materials because they are similar in physical characteristics to natural aggregates. However, whenever such byproducts as bottom ash and dredged soils are used, the energy efficiency of recycling is offset to a certain degree by emissions from transportation. The objective of this study is to analyze the environmental efficiency of recycling bottom ash and dredged soils through the estimation of CO2 emissions, considering both transportation distance and the mixing ratio. Agricultural reservoirs were selected as the final destinations of these recycled materials. This analysis demonstrated that using 100% bottom ash emits less CO2 than using natural aggregates when the ash is transported less than 35.15 km. This breakeven distance increases exponentially with the mass fraction of admixed dredged soil. However, admixture with natural soils does not affect the breakeven distance. Using the breakeven distances, the effective area with which it is efficient to recycle bottom ash was delineated. When dredged soil is admixed to a mass fraction of 70%, the effective area covers most of South Korea. In addition, 100% bottom ash was efficient in 1622 reservoirs (9.45%) in terms of CO2 emissions, and the mixture with 30% bottom ash and 70% dredged soils is efficient in 98.83% of all of the reservoirs in Korea. Bottom ash is most useful for reducing CO2 emissions when it is mixed with dredged soils, which are a byproduct of construction found on-site. This result is meaningful because bottom ash and dredged soils are complementary in their physical characteristics, and they need to be mixed before use as construction materials. The recycling of bottom ash becomes even more attractive with anticipated improvements in fuel efficiency.