The Influence of Compaction and Water Conditions on Shear Strength and Friction Resistance between Geotextiles and Ash-Slag Mixture

Abstract

The paper presents the results of tests of the shear strength of the ash-slag mixture taken from the landfill located in Kraków (Poland) and the interfacial friction resistance at the contact between the ash-slag mixture and woven or nonwoven geotextiles. The tests were carried out in a direct shear apparatus on samples with and without water saturation. The samples for testing were formed in the apparatus box at the optimum moisture by compacting them to I S = 0.90 and 1.00. The test results reveal that the shear strength parameters of the ash-slag mixture were large. It was stated the significant influence of the compaction, the growth of which has resulted in an increase in the angle of internal friction (from 7% to 9%) and cohesion (from 60% to 97%). Whereas the saturation of the samples reduced the shear strength parameters (from 4% to 6%, of the internal friction angle and 30% to 43% of cohesion). The values of the interfacial friction resistance at the contact between the ash-slag mixture and the geotextiles were large as well, but slightly smaller than the values of the shear strength parameters of the mixture itself. The compaction caused an increase in the angle of interfacial friction (from 1% to 5%) and adhesion (from 31% to 127%). The water-saturation of the samples caused a change in the angle of interfacial friction (from −6% to 3%) and decline in the adhesion (from 22% to 69%). Values of the interaction coefficient were about 0.8-1.0 and they tended to rise with increasing the normal stress. Higher values of this parameter were obtained in tests with water saturation and for non-woven geotextiles.Another problem is the proper selection of a backfill material and its compaction. It is usually recommended to use materials with a high shear strength. As a filling, industrial wastes arising, for example, in the production of coal (coal shales), electricity or heat as a result of the coal combustion (ash slag mixtures, fly ash, slag, microsphere, ashes from the fluidized furnace) are also increasingly used. Wastes are generated in the combustion processes because there are large amounts of non-flammable substances, their content in coal ranges from 11% to 17% (hard coal extracted in Poland) and from 3% to 11% (lignite) [8]. The by-products of combustion can be used as artificial aggregates in earth structures [8][9][10][11]. The utilisation of these products in earth structures is of great importance from the economic and ecological points of view. The use of artificial aggregates and geosynthetics for strengthening the soil subgrade also has a significant impact on the protection of natural aggregates. It makes possible constructing the embankments of the selected industrial wastes and limits the scope of soil exchange.In order to meet current requirements for earthworks, the use of geosynthetics that satisfy the requirements for acceleration and quality of works, as well as the optimization of costs of road pavement construction, have been started [12]. In addition to the versatility of using geosynt...