Mechanical Properties of Tailings : Basic Description of a Tailings Material from Sweden

Sammanfattning: Tailings dams are constructed to store waste material from mining industry and usually these dams are raised with time depending upon production rate. Tailings material is sometimes used in construction of tailings dams. Tailings are artificial material and the behavior of tailings material upon loading is different compared to natural soil materials. The mechanical properties of tailings have influence on the performance of a tailing dam. Since the tailings dams are constructed to withstand for long times, it is essential to understand tailings materials in depth in order to assure safe existence of the dams in short term as well as in long term perspective. This licentiate thesis describes the present work carried out on sulphide rich tailings from one mine in Sweden. The material presented is based upon material from three different papers. The first paper describes the basic characteristics of tailings which includes; specific gravity, phase relationships, particle size, particle shape and direct shear behavior. The second paper discusses direct shear tests carried out on tailings from one Swedish mine. Shear strength parameters are evaluated and results from 27 tests (15 drained and 12 undrained tests) are discussed. This paper also describes the vertical height reductions observed during direct shear tests. The third paper focuses on the laboratory results from triaxial tests conducted on tailings materials. This paper shows the drained behavior of tailings under application of different consolidation pressures.The results from particle analysis showed that smaller particles were very angular and bigger particles were sub angular. The material was classified as silt and silty sand. The average particle density (ρs) is 2.83t/m3. The dry density and void ratios were found to be 1.18–1.65 t/m3 and 0.72–1.41 respectively. During direct shear tests vertical height reductions were observed with slight increment in pore pressures. The strain hardening behavior was observed in both drained and undrained conditions in direct shear tests. The strength parameters determined in triaxial test were higher than of those calculated in direct shear tests. Friction angle ϕ' in triaxial tests were found to be 39 to 41degrees and it did not showed any effect with relation to depth. The cohesion and friction angle in direct shear test at 0.15radian, in drained tests were found as in range of 9.7-33.7kPa and 12.5-18.3 degrees respectively. The same parameters for undrained tests were found as 7.1-16.1 kPa and 16.0-20.4 degrees for cohesion and friction angle respectively.