Effects Of Transient Hydro Mechanical Cemented Paste Tailings Properties On One Dimensional Deposition Behaviour
Download Effects Of Transient Hydro Mechanical Cemented Paste Tailings Properties On One Dimensional Deposition Behaviour PDF/ePub or read online books in Mobi eBooks. Click Download or Read Online button to get Effects Of Transient Hydro Mechanical Cemented Paste Tailings Properties On One Dimensional Deposition Behaviour book now. This website allows unlimited access to, at the time of writing, more than 1.5 million titles, including hundreds of thousands of titles in various foreign languages.
Effects of Transient Hydro-mechanical Cemented Paste Tailings Properties on One-dimensional Deposition Behaviour
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
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
[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).