In Situ Properties And Liquefaction Potential Of Cemented Paste Backfill Microform
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In Situ Properties And Liquefaction Potential Of Cemented Paste Backfill Microform
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Author : Kim-Anne Le Roux
language : en
Publisher: National Library of Canada = Bibliothèque nationale du Canada
Release Date : 2004
In Situ Properties And Liquefaction Potential Of Cemented Paste Backfill Microform written by Kim-Anne Le Roux and has been published by National Library of Canada = Bibliothèque nationale du Canada this book supported file pdf, txt, epub, kindle and other format this book has been release on 2004 with categories.
Mercury intrusion porosimetry as well as semi-qualitative image analysis techniques such as scanning electron microscopy, microCT and visual analysis software were used to develop an understanding of the structure developed in field CPB in both the macro and micro scale. Standard oedometer consolidation testing with a modified loading rate was used to investigate the interrelationship of loading rate, which simulates rate of paste accumulation in a stope and the hydration of binder of the paste. The results show that the structure that develops is sensitive to both the binder content of the CPB and the rate of paste accumulation. Cemented paste backfill (CPB) has gained increasing popularity in the last 5 to 10 years and is used routinely in several mines. However, most of the CPB designs are based on laboratory prepared CPB material properties and there is growing awareness that the field CPB may be different from the laboratory prepared material. A field based investigation quantified the extent to which the field material differs from laboratory material. Not only is the field material more heterogeneous than expected, but on average it has a higher void ratio and a lower degree of saturation. These differences impact the performance of the field material. Numerical analysis using FLAC 3D was undertaken to show the influence of the field condition on the stability of the CPB. This research provides practical recommendations for industrial application and provides a framework for further investigation of CPB. Several research projects arising from this initial work are already underway through the Lassonde Institute at the University of Toronto, and several more are at the proposal stage. Static and dynamic liquefaction testing of early age CPB showed that liquefaction due to self-weight alone is unlikely but that blasting too close to the CPB can mobilize the material. Practical recommendations such as limiting blasting in proximity to early age CPB and cordoning off vulnerable areas during the critical initial 24 hr period that the paste is vulnerable to dynamic liquefaction. The cyclic liquefaction results are believed to be the first reported for cemented paste backfill.
A Study Of The Geotechnical Characteristics And Liquefaction Potential Of Paste Backfill
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Author : Khosrow Aref
language : en
Publisher:
Release Date : 1988
A Study Of The Geotechnical Characteristics And Liquefaction Potential Of Paste Backfill written by Khosrow Aref and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1988 with categories.
"The Tailspinner system was developed to produce paste backfill. This system dewaters the full stream tailing material from approximately 55% to 24% water content. These densified tailings are mixed with cement prior to placement in a stope." --
Liquefaction Of Early Age Cemented Paste Backfill
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Author : Abdolreza Saebimoghaddam
language : en
Publisher:
Release Date : 2010
Liquefaction Of Early Age Cemented Paste Backfill written by Abdolreza Saebimoghaddam and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Modern mines require systems that quickly deliver backfill to support the rock mass surrounding underground openings. Cemented Paste Backfill (CPB) is one such backfilling method, but concerns have been raised about CPB's liquefaction susceptibility especially when the material has just been placed, and if it is exposed to earthquakes or large mining induced seismic events. Conventional geotechnical earthquake engineering for surface structures is now relatively advanced and well accepted, and so the objective of this thesis is to consider how that framework might be extended to assess the liquefaction potential of CPB. Seismic records were analyzed for earthquakes and for large mining induced events. Important seismological trends were consistent for rockbursts and earthquakes when the signals were recorded at distances as proximate as one kilometre, suggesting that the conventional earthquake engineering approach might plausibly be adapted for such design situations. For production blasts and for more proximate locations to rockbursts, much higher frequencies dominate and therefore new design methods may be required. Monotonic triaxial tests conducted on normally consolidated uncemented mine tailings demonstrated that the material is initially contractive up to a phase transition point, beyond which dilation occurs. Most importantly the material never exhibits unstable strain softening behaviour in compression, and only temporary or limited liquefaction in extension. The addition of 3% binder results in initial sample void ratios that are even higher than their uncemented counterparts, and yet the material friction is slightly enhanced when tested at 4 hours cure. These results suggest that the flow liquefaction phenomenon commonly associate with undrained loose sand fills will not occur with paste backfill. Cyclic triaxial test results analyzed in terms of number of cycles to failure for a given cyclic stress ratio exhibited a trend consistent with previous tests on similar materials. However, the addition of 3% binder and testing at 4 hours cure resulted in an order of magnitude larger number of cycles to failure - a surprising and dramatic increase, suggesting good resistance of the material to cyclic mobility. Future research is recommended to build on these results and develop more robust methods for liquefaction assessment of CPB.
Assessment Of The Modified Cuaps Apparatus To Estimate In Situ Properties Of Cemented Paste Backfill
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Author : Erol Yilmaz
language : en
Publisher:
Release Date : 2010
Assessment Of The Modified Cuaps Apparatus To Estimate In Situ Properties Of Cemented Paste Backfill written by Erol Yilmaz and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with Compressive strength categories.
This paper evaluates some improvements in the design of a laboratory apparatus called curing under applied pressure system (CUAPS) designed to estimate in situ properties of cemented paste backfill (CPB). This apparatus is effective in conducting the following tests on samples during curing: (i) One-dimensional consolidation test with or without pore water pressure (PWP) measurement, (ii) PWP dissipation test, (iii) saturated hydraulic conductivity (permeability) test, and (iv) curing under constant or variable vertical pressure. Unconfined compression tests can be also performed on consolidated CPB samples after each of these tests. The modified CUAPS apparatus is assessed in this paper. Preliminary results are promising and validate the functionality of the CUAPS apparatus, which will contribute to the knowledge on consolidation behaviour of in situ CPB material.
Microscale Analysis Of Cemented Paste Backfill Microform
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Author : Dragana Simon
language : en
Publisher: Library and Archives Canada = Bibliothèque et Archives Canada
Release Date : 2005
Microscale Analysis Of Cemented Paste Backfill Microform written by Dragana Simon and has been published by Library and Archives Canada = Bibliothèque et Archives Canada this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with categories.
This study shows that wave-based techniques provide insight into some of the factors that affect the behaviour of CPB. Electromagnetic wave-based measurements are sensitive to changes in structure, free water content, bound water content, and ion availability and/or mobility. This research shows that the effective conductivity is a useful parameter to monitor the hydration process, even in low cement content pastes. Shear wave-based measurements are a useful tool to monitor the stiffness evolution in CPB. Apparent yield stress measurements are sensitive to particle-particle interactions and reflect changes in the material's composition, including water content, binder content and type, and chemical additives. All tests show that during the early stages, Portland cement hydration has little effect on the microstructure development, stiffness and flow characteristics of cement-containing pastes. The macroscopic properties of cemented paste backfill (CPB), including fluidity and strength, depend on particle-particle and particle-fluid interactions; thus, it is important to determine the fundamental interactions between the paste constituents to optimize paste design. Specific topics of interest in this study include the effects of paste composition (e.g., binder content and type, and pore fluid chemistry) on the microstructure development, and electromagnetic, rheological and mechanical properties (e.g., setting time, unconfined compressive strength and stiffness) with time. The effect of the pore fluid chemistry on the properties of the CPB depends on the type and amount of the additive. In CPB, calcium chloride and sodium chloride accelerate cement hydration and improve the UCS during the first six months of hydration. Conversely, ferric chloride and hydrochloric acid retard the hydration and setting of CPB. The tested superplasticizers retard cement hydration, increase the UCS and lower the apparent yield stress of CPB. A drawback to using the superplasticizers tested in this study is that a high shear stress is required to re-initiate flow in the pastes.
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).
Geotechnical Characterization Of Cemented Paste Backfill
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Author : Erol Yilmaz
language : en
Publisher: LAP Lambert Academic Publishing
Release Date : 2015-02-10
Geotechnical Characterization Of Cemented Paste Backfill written by Erol Yilmaz and has been published by LAP Lambert Academic Publishing this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015-02-10 with categories.
Cemented paste backfill (CPB) technology is now widely utilized by most modern underground hard rock mines in Canada, Australia, the United States, South Africa and Turkey. CPB is a cementitious material produced with three ingredients: filtered wet tailings, hydraulic binders, and mixing water to ensure the paste's flowability in pipeline for final deposition. This book investigates CPB technology using a recently designed lab apparatus called CUAPS (curing under applied pressure system) that estimates in situ CPB conditions. The CUAPS apparatus has been demonstrated as a practical and cost-effective tool that effectively replaces the traditional approach using non-perforated plastic moulds. The results obtained with the CUAPS apparatus will contribute to improve the safety of mines and miners and provide a better understanding of paste backfill. Each section of this book represents an original contribution to the science and engineering of paste backfill. This book provides some theoretical and experimental bases for designing paste backfill mixtures in terms of cost savings and safety and for incorporating in situ backfill behaviour and properties.
Shaking Table Testing Of Cyclic Behaviour Of Fine Grained Soils Undergoing Cementation
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Author : Imad Hazim Alainachi
language : en
Publisher:
Release Date : 2020
Shaking Table Testing Of Cyclic Behaviour Of Fine Grained Soils Undergoing Cementation written by Imad Hazim Alainachi 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.
Cemented paste backfill (CPB) is a novel technology developed in the past few decades to better manage mining wastes (such as tailings) in environmentally friendly way. It has received prominent interest in the mining industry around the world. In this technology, up to 60% of the total amount of tailings is reused and converted into cemented construction material that can be used for secondary support in underground mine openings (stopes) and to maximize the recovery of ore from pillars. CPB is an engineered mixture of tailings, water, and hydraulic binder (such as cement), that is mixed in the paste plant and delivered into the mine stopes either by gravity or pumping. During and after placing it into the mine stopes, the performance of CPB mainly depends on the role of the hydraulic binder, which increases the mechanical strength of the mixture through the process of cement hydration. Similar to other fine-grained soils undergoing cementations, CPB's behavior is affected by several conditions or factors, such as cement hydration progress (curing time), chemistry of pore water, mixing and curing temperature, and filling strategy. Also, it has been found that fresh CPB placed in the mine stopes can be susceptible to many geotechnical issues, such as liquefaction under ground shaking conditions. Liquefaction-induced failure of CPB structure may cause injuries and fatalities, as well as significant environmental and economic damages. Many researches studied the effect of the aforementioned conditions on the static mechanical behavior of CPB. Other researches have evaluated the liquefaction behavior of natural soils and tailings (without cement) during cyclic loadings using shaking table test technique. Only few studies investigated the CPB liquefaction during dynamic loading events using the triaxial tests. Yet, there are currently no studies that addressed the liquefaction behavior of CPB under the previous conditions by using the shaking table technique. In this Ph.D. study, a series of shaking table tests were conducted on fresh CPB samples (75 cm × 75 cm ×70 cm), which were mixed and poured into a flexible laminar shear box (that was designed and build for the purpose of this research). Some of these shaking table tests were performed at different maturity ages of 2.5 hrs, 4.0 hrs, and 10.0 hrs, to investigate the effect of cement hydration progress on the liquefaction potential of CPB. Another set of tests were conducted to assess the effect of the chemistry (sulphate content) of the pore-water on the cyclic response of fresh CPB by exposing cyclic loads on couple of CPB models that contain different concertation of sulphate ions of 0.0 ppm and 5000 ppm. Moreover, as part of this study, series of shaking table test was conducted on CPB samples that were prepared and cured at different temperatures of 20oC and 35oC, to evaluate the effect of temperature of the cyclic behavior of CPB. Furthermore, the effect of filling strategy on the cyclic behavior of fresh CPB was assessed by conducting set of shaking tables tests on CPB models that were prepared at different filling strategies of continuous filling, and sequential or discontinuous (layered) filling. The results obtained show that CPB has different cyclic behavior and performance under these different conditions. It is observed that the progress of cement hydration (longer curing time) enhances the liquefaction resistance of CPB, while the presence of sulphate ions diminishes it. It is also found that CPB mixed and cured in low temperature is more prone to liquefaction than those prepared at higher temperatures. Moreover, the obtained results show that adopting the discontinuous (layered) filling strategy will improve the liquefaction resistance of CPB. The finding presented in this thesis will contribute to efficient, cost effective and safer design of CPB structures in the mine areas, and will help in minimizing the risks of liquefaction-induced failure of CPB structures.
Early Age Mechanical Behavior And Stiffness Development Of Cemented Paste Backfill With Sand
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Author : Abdullah Abdelaal
language : en
Publisher:
Release Date : 2011
Early Age Mechanical Behavior And Stiffness Development Of Cemented Paste Backfill With Sand written by Abdullah Abdelaal and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Early Age Mechanical Behavior And Stiffness Development Of Cemented Paste Backfill With Sand
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Author : Abdullah Muhammad Galaa Muhammad Idris Abdelaal
language : en
Publisher:
Release Date : 2011
Early Age Mechanical Behavior And Stiffness Development Of Cemented Paste Backfill With Sand written by Abdullah Muhammad Galaa Muhammad Idris Abdelaal and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Rapid delivery of backfill to support underground openings attracted many mines to adopt paste backfilling methods. As a precaution to prevent liquefaction and to improve the mechanical performance of backfills, a small portion of a binder is added to the paste to form the cemented paste backfill (CPB). Recently, adding sand to mine tailings (MT) in CPB mixes has attracted attention since it enhances the flow and mechanical characteristics of the pastefill. This thesis investigates the effects of adding sand to CPB on the undrained mechanical behavior of the mixture (CPBS) under monotonic and cyclic loads. Liquefaction investigations took place at the earliest practically possible age. Beyond this age, the present research focused on characterizing the evolution of stiffness and obtaining the values of the stiffness parameters that could be useful for designing and modeling backfilling systems.The evolution of effective stiffness parameters for two CPB-sand mixtures was monitored in a non-destructive triaxial test for five days. Self-desiccation was found to not be influential on the development of early age stiffness. Moreover, a framework is suggested to predict the undrained stiffness at degrees of saturation representative of the field. The credibility of the proposed test in providing stiffness parameters at representative strain levels of the field was verified.The liquefaction investigation involved monotonic compression and extension triaxial tests. Neither flow nor temporary liquefaction was observed for all cemented and uncemented specimens under monotonic compression, while temporary liquefaction was observed for all specimens under monotonic extension. The addition of binder and sand to MT was found to slightly strengthen the pastefill in compression while weakening it in extension. Under cyclic loading, the addition of sand negatively impacted the cyclic resistance. However, binder was found to be more effective in the presence of sand. All specimens exhibited a cyclic mobility type of response.