Effects Of Transient Hydro Mechanical Cemented Paste Tailings Properties On One Dimensional Deposition Behaviour
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Effects Of Transient Hydro Mechanical Cemented Paste Tailings Properties On One Dimensional Deposition Behaviour
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Author : Mohammad Shahsavari Goughari
language : en
Publisher:
Release Date : 2020
Effects Of Transient Hydro Mechanical Cemented Paste Tailings Properties On One Dimensional Deposition Behaviour written by Mohammad Shahsavari Goughari and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.
When underground mining voids are filled with Cemented Paste Backfill (CPB) a dynamic interaction occurs between the hydrating CPB's engineering properties (hydraulic conductivity, stiffness and strength) and the fill rise rate, drainage conditions, and underground atmospheric conditions. These interactions are particularly important in the first 24 hours after a fill layer's placement in order to support continuous filling. Unfortunately, most previous studies started taking measurements at one day or more, missing this critical initial period. The work presented in this thesis obtains representative material properties at curing times as soon as 30 minutes. Four stages of hydraulic conductivity evolution are linked to corresponding stages of binder hydration at times from 30 minutes to 5 days, and it is shown conventional measurement methods could under-estimate initial hydraulic conductivity by an order of magnitude. Consolidation tests with virtually continuous loading rates simulated effective stress development onsets between 4 and 48 hours, at rates between 5 and 20 kPa/hr and final level of 400 kPa. In virtually continuous loading it is impossible to deconvolve the parameters controlling the ultimately achieved void ratio and stiffness, but a graphical technique is developed to aid preliminary design and determine likely void ratios that should be used in other laboratory tests for engineering properties. The hydraulic conductivity and consolidation element test results are then used to interpret results from four mesoscale laboratory experiments that simulate continuous backfilling. These tests demonstrate the importance of properly simulating the underground atmospheric conditions, and in placing the fill in the most continuous manner possible. For placement conditions that most closely simulate the actual placement conditions at the studied mine, it is found that virtually no self-weight consolidation occurs and thus the void ratios in the field and in the meso-scale experiments are essentially identical. Therefore, the effective stress path realized in the field will not lead to significant self-weight consolidation and the attendant strength gains that might otherwise occur.
Energy Research Abstracts
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Author :
language : en
Publisher:
Release Date : 1993
Energy Research Abstracts written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1993 with Power resources categories.
Includes all works deriving from DOE, other related government-sponsored information and foreign nonnuclear information.
Effects Of Dynamic Loading On The Geomechanical Behaviour Of Cemented Paste Backfill
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Author : Gonzalo Hernan Suazo Fuentealba
language : en
Publisher:
Release Date : 2016
Effects Of Dynamic Loading On The Geomechanical Behaviour Of Cemented Paste Backfill written by Gonzalo Hernan Suazo Fuentealba and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
[Truncated] Backfill is any material that is placed underground to fill the voids (stopes) left after the process of extracting minerals from crushed rock. Cemented Paste Backfill (CPB) is one of these materials, which consists of a mixture of full stream tailings, a small percentage of cement and water. Underground space is a dynamic environment that subjects these fills to a series of dynamic loading resulting from blasting and seismic events. Refracted stress waves at the CPB-rock interface can increase the shear and compressive stresses in the fill. As a result, excess pore water pressures may develop and liquefaction can eventually be triggered. Liquefaction might cause the failure of the retaining barricade constructed at the bottom of the stope since total pressure can rise to as high as the full hydrostatic head of the fill. However, the amount of dynamic energy transmitted to the fill as well as the liquefaction risk, greatly diminishes as the fill desaturates and negative water pressures arise in the pore space. In this context, the primarily objective of this thesis is to evaluate the liquefaction susceptibility of CPB at early curing ages due to seismic and blasting stress waves. In addition, the propagation phenomena of compressional waves in CPB, the effects of degree of saturation on stress wave refraction at CPB interfaces and the blast response of a backfilled stopes are explored. Finally, the evolution of unsaturated CPB properties and the mechanism of desaturation of the fill are investigated. This research consisted of in situ and experimental testing, and a numerical modelling component.Direct simple shear (DSS) tests were conducted to study the cyclic undrained shear response of CPB. The effects of confining stress, initial static shear stress and void ratio on the liquefaction resistance of uncemented fine-grained tailings was firstly researched. Then, the cyclic response of cemented tailings prepared at different curing ages, cement contents and initial void ratios, was examined. The material, independently of the degree of cementation, showed a predominantly cyclic mobility type response with large degradation of shear stiffness at advanced numbers of shear cycles. However, no flow type of failure was observed in any of the tests conducted. The overburden stress correction factor was found to decrease with increasing confining stresses in the range 100 to 400 kPa and to gradually increase from 400 kPa onwards, when samples were tested at the same initial void ratio. Similarly, higher cement contents, longer curing periods or higher initial solids contents were found to increase liquefaction resistance. A unconfined compressive strength (UCS) of about 70kPa, which corresponds to a shear wave velocity of 220 m/s, was found to be adequate to resist liquefaction under a large earthquake-induced cyclic stress ratio (CSR).
Synergistic And Environmental Benefits Of Using Cement Kiln Dust With Slag And Fly Ash In Cemented Paste Tailings
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Author : Amjad Tariq
language : en
Publisher:
Release Date : 2012
Synergistic And Environmental Benefits Of Using Cement Kiln Dust With Slag And Fly Ash In Cemented Paste Tailings written by Amjad Tariq and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
Many researchers have validated the phenomenon of internal sulphate attack in ordinary Portland cement (CSA Type GU) based cemented paste tailings containing sulphide minerals and have observed secondary gypsum as an ubiquitous phase in such matrices. The secondary gypsum, due to its soft nature and swelling and expansive properties, is principally considered to be the sole culprit responsible for subsequent internal cracking and strength degradation of sulphidic paste at later stages. High Portland cement cost and its apparent poor performance in the long-term in sulphate rich environments advocate for the formulation of resilient cemented paste tailings using economical but efficient binders. This study demonstrates the effectual utilization of selective cement kiln dusts (CKDs) in composite binder systems containing ground granulated blast furnace slag (SL), Type C fly ash (FC) and a small amount of Portland cement. The addition of calcium and alkali rich cement kiln dust in Portland cement-slag and Portland cement-fly ash binder systems functioned as an excellent alkaline activator and accelerator in promoting the hydration mechanisms within cemented paste tailings formulations. High alkaline pore solution created by free calcium rich cement kiln dust (CKD) is capable of disintegrating the solid glassy network of supplementary cementing materials to produce reactive silicate and aluminate compounds. Comparative assessment of a range of binder combinations has been carried out for cemented paste tailings formulations using performance assessment indicators such as unconfined compressive strength, saturated hydraulic conductivity, micro-structure, and contaminant containment capability (leachability). The short-and long-term performance evaluation of the unconfined compressive strength of blended cements in cemented pastes of sulphidic tailings was carried out over a curing period of 480 days. Cement kiln dusts (DA and DH) containing high CaO content (52.4% and 57.8%, respectively) and low Loss on Ignition (LOI), i.e., 5.1% and 4.8%, respectively, performed best in making cemented paste tailings, whereas the paste mixtures containing DB and DL (with very low free lime and very high LOI) as single binders in combination with mine tailings (MT) never hardened. The addition of selective CKD, and SL, and/or FC as partial replacement for Portland cement can improve the performance of the cemented paste tailings containing sulphide minerals and alleviate the strength loss associated with Type GU cement based paste. The behavior is attributed to the latent strength acquisition of SL and FC in the blended cements containing DA and DH as a result of proliferating hydration and augmented pozzolanic reactivity. Previous studies carried out by other researchers on hardened cemented paste tailings specimens containing Portland cement-pozzolans binders confirmed the possibility of the presence of un-reacted or un-hydrated particles of slag and fly ash in such matrices. In the present study, SEM was carried out on cemented paste tailings samples to investigate the effect of using calcium and alkali rich CKD on pozzolanic reactivity of binders containing SL and FC. The effect of incorporation of DA or DH in GU/HS-SL and GU/HS-FC binders was analyzed in high magnification modes. No un-reacted grains of SL and/or FC were found within the crushed surfaces of the matrices. The glassy SL was completely disintegrated by the highly alkaline pore solution when attacked by OH- ions. As well, all the amount of FC used in composite binder system was completely exhausted by the accelerated pozzolanic activity. Concomitantly, the observed microstructure delineation of selected cemented paste tailings samples was found to be well acquiescent with their respective mechanical performance (based on the unconfined compressive strength). The precipitation of calcium hydroxide in Type GU based cemented paste tailings can be inadequate for total blocking of pores within cemented paste tailings matrix. The enhanced pozzolanic reactivity of SL and FC with additional calcium hydroxide produced by the incorporation of high calcium and alkali rich CKD in cemented tailings matrices generated additional hydration products, favoring enhanced pore refinement and densification, which, in turn, reduced the transportability of fluid through the hardened matrices. Meticulous geochemical characterization of cemented paste tailings formulations is imperative, particularly when binders replace the traditional Portland cement. The leaching behavior of metals in cemented paste tailings formulations was studied using field mimicking leaching protocols to obtain information on the fixation involving both chemical stabilization and physical encapsulation mechanisms. Leaching test results based on the Synthetic Precipitation Leaching Procedure (US EPA Method 1312) showed that cemented paste tailings formulated with Type GU cement alone are susceptible to contaminant leaching and, therefore, do not eliminate interaction between the monolith and contact waters. On the other hand, optimized cementing blends containing a small amount of Type GU cement and SL activated by DH offer more efficient contaminant fixation capabilities for tailings pastes. Low calcium cement kiln dust (DL) promoted chemical stabilization only within the resultant composites due to lack of cementitious properties and is, therefore, incapable of providing physical encapsulation of the contaminants. The results advocate the technically beneficial synergy of composite binders containing selective CKDs for paste preparation in contrast with Portland cement alone, Portland cement-slag, and Portland cement-fly ash binder systems in sulphidic mine tailings management. An optimized mix proportion is however required to achieve optimal performance.