Andrzej Gruchot, Tymoteusz Zydroń
Uniwersytet Rolniczy, Kraków
In Poland, the production of electricity and thermal energy is based mainly on hard and brown coal burning. It causes great amount of furnace waste, including ash-slag mixtures from wet deposition of waste. According to GUS data in 2010 9 million tons of waste were produced and 253.7 million tons are still on landfills being a burden to the environment. One of possible ways of their usage is earthworks, where ash-slag mixtures are allowed to use in low layers of road embankments, under the condition that they will be built in places that are dry or isolated from water. This restriction is a result of high sensitivity of furnace waste for changes in moisture content as well as their high susceptibility to filtration deformations. Therefore it is crucial to determine strength characteristics of this type of materials depending on their moisture content. The purpose of the paper was to determine the influence of moisture content of ash-slag mixture from “Skawina” Power Plant on its shear strength parameters as well as to determine stability of embankments formed from this type of material. Within the scope of laboratory tests, basic geotechnical parameters as well as shear strength parameters and permeability of ash-slag mixture were determined. Shear strength tests were carried out in the standard direct shear box apparatus at the compaction indexes IS = 0.90, 0.95 and 1.00. The moisture content was close to optimal and 5% lower or higher than the optimal moisture content. Permeability tests were carried out with the constant hydraulic gradient on samples at the compaction indexes IS = 0.90 and 1.00. Based on obtained results it was stated that ash-slag mixture from “Skawina” Power Plant has high shear strength parameters and relatively high values of permeability coefficient, although values of these parameters greatly depend on mixture compaction. Additionally shear strength tests showed that the moisture content has a great influence on shear strength parameters. Depending on these tests results and using proposal of calculative model by Matsushi-Matsukury effective strength parameters of the mixture were estimated. Comparing calculations results with parameters obtained from the triaxial shear tests it was stated that the proposed model gives safe values of effective strength parameters so they were used for stability calculations for a model road embankment, which was exposed to heavy rainfall. Infiltration calculations were carried out assuming daily intensity of rainfall on 100 mm/day, which corresponds with 1% probability of rainfall for the Kraków area. These calculations showed, that high permeability of the mixture has a significant influence on the range of changes in the slopes moisture content and the accepted rainfall density was insufficient to saturate this material when there is a free water flow in the embankment’s body. This process can occur only in case of the embankment formed from the mixture on the ground that has lower permeability than the mixture. Calculation results showed that embankment formed from the mixture at high compaction had a high value of safety factor, which indicates that the ash-slag mixture can be a valuable substitute for natural soils.
właściwości geotechniczne; budownictwo ziemne
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