Investigating the hydrogeotechnical and microstructural properties of cemented paste backfill using the CUAPS apparatus
Başlık çevirisi mevcut değil.
- Tez No: 401200
- Danışmanlar: DR. TIKOU BELEM, DR. MOSTAFA BENZAAZOUA, DR. BRUNO BUSSIERE
- Tez Türü: Doktora
- Konular: Çevre Mühendisliği, Environmental Engineering
- Anahtar Kelimeler: Mine tailings, Cemented paste backfill, One-dimensional consolidation, saturated hydraulic conductivity, Pore pressure, Cement hydration, Curing stress, Compressive strength
- Yıl: 2010
- Dil: İngilizce
- Üniversite: Université du Québec en Abitibi-Témiscamingue
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 432
Özet
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Özet (Çeviri)
In the mining and mineral industry worldwide, large volumes and many varieties of mine tailings consisting of coarse and fine fractions that are either reactive (acid generating) or non-reactive are produced every day. Most mining operations use the coarse fraction of the tailings for underground backfill, while the fines are usually deposited on the surface into tailings impoundments or dams. However, it is well known that these dams are at risk of failure due to leakage, instability, liquefaction and inadequate design. Moreover, unless they are properly managed, acid-generating tailings can cause significant environmental damage by generating acid mine drainage that releases heavy metals. Overcoming such problems requires tailings management approaches that are technically suitable, economically viable, environmentally sustainable and socially responsible. Cemented paste backfill (CPB), an engineering material, is used in a recent, innovative tailings management method. Typically, CPB is a mixture of total mill tailings without removing the fines, or desliming (70–85 wt% solids), and single, binary and ternary hydraulic binders (3–7 wt%) in order to meet stability requirements and combined with mixing water (20–25 wt%). Most studies to date have focused on the physicochemical, mineralogical, mechanical and microstructural properties of CPB. Conventional undrained plastic moulds (non-perforated) are usually used to determine mine backfill design parameters, depending on the solids mass concentration, grain size grading, binder type and content, and curing time. However, recent studies have shown that for identical backfill recipes used in the laboratory and in situ after a given curing time, the performance (i.e., mechanical strength) of laboratory-prepared CPB samples is consistently lower than that obtained from in situ CPB samples. The primary reason is that in situ backfill material is cured under effective stresses that develop gradually in a stope due to self-weight and/or time-dependent consolidation loads, which accelerate the rate of final strength development. In situ CPB placement and properties cannot be replicated using conventional moulds. Therefore, innovative equipment and test procedures that allow realistic reproduction of in situ curing conditions of CPB materials in a controlled laboratory setting are needed. The aim is to obtain higher or at least equivalent mechanical strength, and consequently a better backfill design. This thesis comprises four separate peer-reviewed journal manuscripts. The first paper investigates differences in CPB hydromechanical properties between laboratory and in situ curing conditions using the original version of a recently developed laboratory apparatus called CUAPS (curing under applied pressure system). It consists of an in-depth examination of the physical, hydrogeotechnical and geochemical properties of CPB samples prepared using a coarse-grained tailings (15 wt% finer than 20 μm < 35 wt%) sample from a European polymetallic mine. The second paper assesses an improved CUAPS apparatus that allows estimating certain in situ hydromechanical properties of CPB, including anisotropic compression and permeability behaviour. The improved CUAPS apparatus accurately captures the axial deformation that occurs in backfill as it compresses (either by surcharge load or self-weight). This allows performing not only one-dimensional consolidation testing, but also pore water pressure (PWP) dissipation testing, permeability testing (saturated hydraulic conductivity), and curing under applied effective stresses and compression rate dependent curing conditions. Preliminary results show the capacity, efficiency and usefulness of this improved CUAPS apparatus: it can be used to optimize more realistic paste backfill mix designs for use in underground backfilling. The third paper investigates the one-dimensional consolidation properties of early age CPB material, which are closely related to their permeability (saturated hydraulic conductivity), using the improved CUAPS apparatus. CPB samples were prepared using a medium-grained tailings (35 wt% finer than 20 μm < 60 wt%). The fourth and last paper investigates the effect of curing conditions (consolidated and non-consolidated) on CPB microstructural properties using empirical mercury intrusion porosimetry (MIP) results and specific surface area measurements. Some predictive equations for unconfined compressive strength of CPB materials are proposed based on the certain microstructural parameters. This Ph.D. thesis not only provides a better understanding of the properties of laboratory-prepared CPB samples, but also assesses the improved CUAPS apparatus, a valuable tool for collecting equivalent in situ mine backfill data at laboratory scale. It constitutes an original study on the one-dimensional consolidation behaviour of CPB samples at various curing times as well as the behaviour of samples cured under a series of incremental pressures, which allows the effective stress to develop gradually (simulating CPB-filled underground stopes). This research effort has contributed to a better understanding of the behaviour of CPB, a relatively complex material. Moreover, it proposes a strength performance testing procedure that can be incorporated into the design process of any CPB material. Finally, the improved CUAPS apparatus can help backfill researchers and practitioners better understand the consolidation properties of fresh or hardened laboratory-prepared CPB samples.
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