M. Borys, P. Filipowicz

GEOTECHNICAL PARAMETERS of COAL MINING wasteS
FROM LUBLIN COAL BASIN

S u m m a r y

Waste materials from industry like coal mining wastes, dust-slag compound, aggregates based on coal mine wastes and materials produced after processing contaminated soils are more and more often used for building purposes instead of natural soils. Large amounts of coal mine wastes are used to restore opencast aggregate mines, to build or rebuild local roads, to build or modernise the bodies of embankments including flood embankments, dikes around channels and water reservoirs and to produce building materials.

Understanding environmental impact and knowledge of chemical composition of these materials and their water eluates and finally their geotechnical parameters are necessary to use them as building grounds. Grain size distribution , maximum bulk density of solid particles, optimal moisture content , shear strength of soil and coefficient of permeability have been tested to utilise these materials in hydrotechnical constructions e.g. in building flood embankments.

Performed analysis of grain size structure in mine wastes from Lublin Coal Mine revealed a clear effect of the storage time on obtained results . In all analysed samples gravel fraction was largest and constituted from 73 to 86% in fresh wastes, from 58 to 77% in 5 years old wastes and from 51 to 67% in 7 years old wastes. The older were the wastes the less coarse and the more fine particles they contained.

There is a clear tendency of decreasing maximum bulk density of solid particles and increasing optimum moisture content of mine wastes with the time of their storage in a heap.

Waste materials were characterised by high angle of internal friction (24o-55o) and high cohesion (21-67 kPa), higher than natural compact grounds of similar grain size distribution. The angle of internal friction was observed to decrease and cohesion was found to increase with the age of mine wastes. The former decreased by 33% on average and the latter increased by 11% after 7 years of storage in a heap.

Analysed coal mine wastes may be classified as moderately and poorly permeable. Their coefficient of permeability is similar to that of mineral soils like fine, silted and loamy sands. The coefficient decreases with the time of their storage on a stockpile.

The effect of weathering is also presented on some geotechnical parameters of the coal mining wastes from Lublin Coal Basin built in hydrotechnical construction. The analysis was performed for embankments of different age.

In samples collected from 10 years old dike the percentage share of particular size fractions was similar to that of fresh coal mining wastes. Apparent angle of internal friction measured with the direct shear apparatus in samples from the dike ranged from about 31 to 50o and cohesion ranged from about 20 to 51 kPa. These samples had coefficient of permeability in the range between 10 ^-8 and 10 ^-5 m·s ^-1.