Charakterystyka zmian deformacyjnych gruntów antropogenicznych z osadników cukrowni

Krystyna Choma-Moryl


Characterization of deformation changes in anthropogenic soil from the wet dumps of sugar factories.
A b s t r a c t. Sewer sludge that fills four wet dumps of the closed Małoszyn Sugar Factory in Malczyce near Środa Śląska, Lower Silesia constitutes a very specific anthropogenic soil. It is composed of grains and mineral particles transported in suspension after sugar beets pre-processing treatment. Presently the wet dumps are to be recultivated to meet the requirements of environmental protection. According to the recultivation project the wet dumps will be backfilled with suitable waste material and covered with sand and soil to stimulate soil forming processes. Finally grass, clover and shrubs will be introduced. The recultivation layer thickness will reach 3–6 m. Anthropogenic soil that fills the wet dumps is up to 2–3 m thick. The grain size distribution is generally consistent with silty loam, silty clay loam and silty clay. Quartz, illite and chlorite dominate the mineral composition. The wet dump’s bottom is formed by clays of the Poznań Formation, practically impermeable. Silt-dominated soils deposited in a water environment are highly susceptible to deformations caused by water and overload. Deformation behaviour was studied for the soil in a semi-solid state as well as in a soft-plastic state. Varying influence of water results, among others, in shrinkage (LS) and swelling of the soils, characterized in the present study by swelling strain (εp). Load-induced deformation of the soils is described basing on the modulus of primary compressibility. Basing on the results obtained it may be stated that the investigated anthropogenic soil undergoes moderate deformations under the influence of water. The swelling strain does not exceed 0.5–1.2% for the soil in a soft-plastic state and amount to 3.1–4.3% in a semi-solid state. The soil shrinkage limit varies between 3 and 5%. On the other hand load-induced deformations will be of remarkably higher importance. The soil in a soft-plastic state shows high shrinkage that is comparable with the one for organic soils. The modulus of primary compressibility is 282.3–925.9 kPa. The compressibility is markedly lower for a semi-solid state (MO =1 190.5–2 000 kPa). Characteristically, in both soft-plastic and semi-solid states the soil shows higher compressibility for lower load values 0–50 kPa than for the higher range 0–200 kPa. These compressibility values should be taken into account during backfilling of the wet dumps with various safe waste materials at recultivation. The load-induced pressure, initially low, will increase with adding consecutive layers. Thus highest soil deformations should be expected during the initial backfilling stages and their intensity may be estimated using the modulus of primary compressibility.

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