Testing And Multiphysics Modelling Of The Shear Behaviour Of Rock Cemented Paste Backfill Interface
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Testing And Multiphysics Modelling Of The Shear Behaviour Of Rock Cemented Paste Backfill Interface
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Author : Kun Fang
language : en
Publisher:
Release Date : 2021
Testing And Multiphysics Modelling Of The Shear Behaviour Of Rock Cemented Paste Backfill Interface written by Kun Fang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
Cemented paste backfill (CPB) is an innovative technology developed in the mining industry during the last few decades. It has been adopted worldwide by many underground mines for its tremendous advantages: (1) mining space is stabilized by pumping cemented paste backfill into the underground cavities created by mining activity, which is critical to the safety of mine workers; (2) the consumption of tailings (which is stored at the ground surface and is a major source of acid mine drainage (AMD)) is beneficial for environmental protection and community safety; (3) due to the supporting effect of the CPB structure on underground cavities, the recovery ratio is significantly increased; and (4) CPB structures can also carry heavy equipment when mining the adjacent orebody, facilitating mining operations. How to design a safe and cost-effective CPB structure is a key task or challenge for mining engineers and researchers. Mechanical stability is one of the most important design criteria. This stability is mainly a function of the uniaxial compressive strength (UCS) of CPB body and the shear strength/behaviour of the CPB-rock interface. Given the lower friction angle and adhesion of the CPB-rock interface (in comparison with the friction angle and cohesion of CPB body), a thorough understanding of the shear strength/behaviour of the interface is critical for a cost-effective geotechnical design of underground CPB structures. However, only limited studies have been conducted to date on the shear performance of the CPB-rock interface, and no studies have taken into consideration the effects of different factors (e.g., temperature, sulphate ions, self-weight or surface morphology) on the shear behaviour of the CPB-rock interface. Moreover, no multiphysics interface model is currently available that incorporates the aforementioned factors to describe and predict the CPB-rock interface shear behaviour. This research gap was therefore addressed in this PhD study. In this PhD research, a series of laboratory tests were conducted assessing the effects of sulphate content, temperature, curing stress, drainage condition and interface roughness on the shear strength/behaviour of the interface between CPB and rock. The results obtained so far indicated that sulphate and temperature can either positively or negatively affect the shear strength of the CPB-rock interface, depending on the initial sulphate contents and curing time. In terms of the effect of temperature, the shear strength and shear strength properties generally increased with temperature. However, high temperature (≥ 35°C) resulted in an adverse effect on the shear strength because of the crossover effect. In addition, higher curing stress benefitted to the shear strength acquisition of the interface and, due to the increased effective stress and matrix suction, the drained condition increased shear strength as well. As for the effect of surface morphology, the shear strength of the CPB-rock interface rose with surface roughness. Furthermore, chemo-elastic as well as coupled thermo-chemo-mechanical cohesive zone models (CZMs), which take the sulphate attack and temperature-induced acceleration in the cement hydration into consideration, are also developed to simulate the shear strength and behaviour of the CPB-rock interface. The proposed models can well capture the shear behaviour of the interface under different loading conditions. Besides, they also numerically attest to the importance of the shear resistance of the CPB-rock interface in controlling stress distribution in CPB structures. The results obtained from experimental tests, numerical modelling and simulations concerning the shear behaviour of the CPB-rock interface under different multiphysics conditions provided useful information for understanding and more effectively assessing the shear strength and behaviour of the interface between a CPB structure and rock mass, which is critical for the design of safer and more cost-effective CPB structures.
Fatigue Mechanical Behaviors Of Rock Backfill Composites Laboratory Study
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Author : Yu Wang
language : en
Publisher: Scientific Research Publishing, Inc. USA
Release Date : 2024-07-18
Fatigue Mechanical Behaviors Of Rock Backfill Composites Laboratory Study written by Yu Wang and has been published by Scientific Research Publishing, Inc. USA this book supported file pdf, txt, epub, kindle and other format this book has been release on 2024-07-18 with Antiques & Collectibles categories.
This book is intended as a reference book for advanced graduate students and re-search engineers in rock mechanics related to mining engineering. The cemented tailings backfill (CTB) technique is widely used in deep underground mining, since this tech-nique is effective to support surrounding rock, control rockburst, reduce ground sub-sistence, and reduce surface disposal of tailings. Plenty of investigations have been attempted to experimentally or numerically evaluate the strength of CTB with different components (e.g., mixture of cement, tailings, fly ash, blast furnace slag, etc.) to ensure the geological stability when extracting adjacent stopes. After extracting ore from stopes, CTB is filled in the gob, stress redistribution occurs in the backfill stope and surrounding rocks. Due to the elasticity mismatch of these two kinds of material, differential de-formation occurs and they both resist the overburden pressure and deformation. As a result, the interactions between the surrounding rock and tailing backfill material have significant role in maintaining the long-term stability of mine stopes. Apart from the investigations on the static mechanical behaviors of rock- backfill composited backfill (RBCS) material, the RBCS in the stope are also exposed to disturbed stress (e.g., blast vibration, excavation, earthquake, etc.), and the disturbed stress is usually equivalent to cyclic or fatigue loads. As a result, investigations on rock-backfill interactions subjected to the disturbed stress are critical and significant to maintain the long- term stability of mine stopes.
Engineering Geology For A Habitable Earth Iaeg Xiv Congress 2023 Proceedings Chengdu China
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Author : Sijing Wang
language : en
Publisher: Springer Nature
Release Date : 2024-09-18
Engineering Geology For A Habitable Earth Iaeg Xiv Congress 2023 Proceedings Chengdu China written by Sijing Wang and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2024-09-18 with Science categories.
This book collects the selected papers of the XIV Congress of the International Association for Engineering Geology and the Environment held in Chengdu, Sichuan, China from September 21st - 27th, 2023, with the theme of Engineering Geology for a Habitable Earth. The meeting proceedings analyses the dynamic role of engineering geology in our changing world. The congress is expected to enhance the inter-disciplinary research development of international engineering geology and the environment, and contribute to the advancement of major projects, ecological progress, and habitable earth with in-depth discussion in the area of engineering geology and global climate change, geological hazard assessment and prevention, geotechnical properties of rock and soil mass, engineering geology and the environmental issues concerning marine, transportation, urban and ecological environment protection, engineering geology and resilience engineering construction, intelligent engineering geology, and new theories, methods, and techniques in engineering geology.
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).
Investigations Of Backfill Rock Mass Interface Failure Mechanisms
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Author : Stylianos Manaras
language : en
Publisher:
Release Date : 2009
Investigations Of Backfill Rock Mass Interface Failure Mechanisms written by Stylianos Manaras and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
From previous research, it has been proven that rock roughness and closure are two important factors for stability of backfilled stope and exposed backfill. In order to estimate the important parameters of roughness, several investigations have been conducted in other scientific fields to study roughness. The results showed that the important roughness parameters are application-dependent. In geology and rock mechanics the Joint Roughness Coefficient (JRC) is a critical factor that incorporates the roughness in stability problems. Although JRC is widely used, it is very subjective and highly depends on the experience of the individual conducting the analysis. During the last several decades there were attempts to use different methods such as fractal geometry, Fourier analysis, analytical methods, etc. to convert a random surface profile into a JRC. The goal of the current research is to estimate with greater accuracy the contribution of roughness to the shear strength of the interface at the paste-rock contact when backfilling. Four hundred and fifty backfill samples were constructed and tested in a shear box. The variables of the tests are three: binder percentage, roughness and cure time. From the test results the importance of each of those parameters to the final shear strength of the paste-rock interface was estimated. The normal stress that acts on the samples is also a critical factor. From the tests that were tried, it was concluded that there are limits in normal stress for which roughness is important.
Mechanical Properties Of Cemented Paste Backfill Under Low Confining Stress
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Author : Andrew Ning Pan
language : en
Publisher:
Release Date : 2019
Mechanical Properties Of Cemented Paste Backfill Under Low Confining Stress written by Andrew Ning Pan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with categories.
Cemented paste backfill (CPB) plays an increasingly important role in the mining industry due to rapid delivery rate, tight-filling characteristics, relatively insignificant water management issues during filling, and generally uniform as-placed mechanical properties. The most common basis for assessing backfill strength is Unconfined Compressive Strength (UCS), and some of the most commonly used design methods have UCS as a fundamental design parameter. However, actual CPB properties and behavior under the range of confining stresses relevant to these design methods has been studied very little. This work uses UCS tests and a novel direct tensile test method and compares test results with strengths obtained from direct shear tests. A form of punching shear was also investigated, but the results were found unsatisfactory for design purposes. For materials with UCS up to about 1 MPa, the UCS and tensile strengths are consistent with the Mohr-Coulomb failure envelope obtained from direct shear tests.
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.
Soil And Rock Behavior And Modeling
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Author : Ronaldo Luna
language : en
Publisher:
Release Date : 2006
Soil And Rock Behavior And Modeling written by Ronaldo Luna and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Technology & Engineering categories.
GSP 150 contains 65 papers on the behavior and modeling of soil and rock presented at the GeoShanghai Conference, held in Shanghai, China, June 6-8, 2006.
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.
Experimental Testing Of Geomechanical Behavior Of Fiber Reinforced Cemented Paste Backfill Fr Cpb Under Warmer Curing Temperature
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Author : Iarley Loan Sampaio Libos
language : en
Publisher:
Release Date : 2020
Experimental Testing Of Geomechanical Behavior Of Fiber Reinforced Cemented Paste Backfill Fr Cpb Under Warmer Curing Temperature written by Iarley Loan Sampaio Libos 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.
Backfilling techniques enable improved ore recovery and structural stability to underground mines employing a material to fill the voids after the excavation. Fiber-reinforced cemented paste backfill (FR-CPB) is this material and it consists of mine tailings, cement, mixing, and fibers. After placed into the underground space (called stope), FR-CPB provides sufficient ground support, enables the exploration of larger amounts of ore since no orebody pillars are required to sustain the excavations, and thus enhances mining production. The reinforcement technique has been considered as a promising approach for the backfilling design. However, regarding that mining activities may take place at a depth of more than 1000 meters, the geothermal gradient can not only change the temperature of FR-CPB but also affect its geomechanical behaviors due to its temperature-dependent characteristics. Therefore, the objective of this research is to experimentally investigate compression, tension, shear, triaxial, and fracture behaviors of FR-CPB subjected to different warmer curing temperatures (20°C, 35°C, and 45°C). Moreover, to identify the mechanisms responsible for the evolution of geomechanical behavior, a series of mold-based monitoring programs have been designed and performed to measure changes related to matric suction, electrical conductivity, and temperature in FR-CPB. Additionally, to determine the progress of binder hydration and associated microstructure change, extensive X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) observation have been conducted at the microscale. The obtained results evidenced that warmer curing temperature can significantly affect the fiber-CPB matrix interfacial interaction. Correspondingly, the geomechanical (including tensile, compressive, shear, and fracture) behavior show strong temperature sensitivity from early to advanced ages. Therefore, the obtained results from the present study can not only improve the understanding of the geomechanical behavior of FR-CPB but also contribute to the safe design of backfill structures in underground mines.