Geotechnical Properties of Washed Mineral Waste from Grit Chambers and Its Potential Use as Soil Backfill and Road Embankment Materials

The current practice of managing washed mineral waste from grit chambers under national legislation focuses primarily on its disposal, generating high costs for wastewater treatment plants. Other ways are being sought to enable its use, especially as a by-product in the construction industry. This paper presents the results of laboratory tests of the geotechnical, physical and mechanical parameters of washed mineral waste from grit chambers. Research samples were taken from the largest, in terms of maximum daily capacity, wastewater treatment plant “Czajka” in Poland. The washed mineral waste was characterized by organic matter content (0.36% by Tyurin’s method or 1.04% by the loss on ignition method), fraction content (sand fraction was at least 90%; it corresponds in grain size to uniform-grained medium sand), specific density of solids (2.55 g/cm3), dry density, void ratio and porosity corresponding to the state of the loosest and densest possible composition of soil grains and particles (1.54 g/cm3, 0.656, 0.396 and 1.87 g/cm3, 0.364, 0.267, respectively), sand equivalent (93), passive capillarity (0.20 m), maximum dry density (1.78 g/cm3), optimal moisture content (11.23%), degree of saturation after compaction (0.66) and permeability coefficient (6.22·10−3cm/s). The mechanical parameters determined included internal friction angle (35.5°) and apparent cohesion (14.27 kPa). The possibility of using washed mineral waste as soil for the backfill of installation trenches, abutments and retaining structures, as well as road embankment material, was evaluated considering current standards and legislation. It was found that the values of the determined parameters of washed mineral waste coincide with the values of the geotechnical parameters of sand, and there is a possibility of using this waste as a material in the indicated applications after fulfilling the appropriate conditions.

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