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Strength evolution and deformation behaviour of cemented paste backfill at early ages： Effect of curing stress, filling strategy and drainage

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International Journal of Mining Science and Technology 2016年第5期26卷 809-817页

作者： Ghirian Alireza fall mamadou Department of Civil Engineering University of Ottawa 161 Louis Pasteur Ottawa K1N 6N5 ON Canada

In this study, a pressure cell apparatus is developed to investigate the early age evolution of the strength and deformation behaviour of cemented paste backfill(CPB) when subjected to various loading conditions under different curing scenarios. The different curing scenarios that are simulated include:(1)drained and undrained conditions,(2) different filling rates,(3) different filling sequences, and(4) different curing stresses. The findings show that drainage, curing stress, curing time and filling rate influence the mechanical and deformation behaviours of CPB materials. The coupled effects of consolidation, drainage and suction contribute to the strength development of drained CPB subjected to curing stress. On the other hand, particle rearrangement caused by the applied pressure and suction development due to self-desiccation plays a significant role in the strength gain of undrained CPB cured under ***, curing stress induces slightly faster rate of cement hydration, which can contribute to strength acquisition.

关键词： Cemented paste backfill Tailings Pore pressure Curing under stress Plug fill Cement

A column study of the hydro-mechanical behavior of mature fine tailings under atmospheric drying

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International Journal of Mining Science and Technology 2017年第2期27卷 203-209页

作者： Anis Roshani mamadou fall Kevin Kennedy Department of Civil Engineering University of OttawaOttawa KIN 6N5Canada

In this paper, the hydro-mechanical behavior and physical properties of mature fine tailings(MFT) under atmospheric drying are investigated through a column study. In the study, evaporation takes place in the development of suction in the upper parts of the column and increasing suction leads to higher strength in the tailings. After 5 days, the suction in the first lift is around 17 k Pa in the upper part of the *** a second lift is added, the first lift initially loses strength but over a 30 days' period, the strength is recovered to its prior value and suction in the second lift reaches 500 k Pa. The vane shear strength values show a substantial increase in the strength of the MFT after 30 days under atmospheric drying and drainage. The 90% strength found in the column exceeds the threshold(5 k Pa). The hydraulic-mechanical properties of the deposited tailings are closely coupled due to several mechanisms, such as evaporation,drainage, self-consolidation, suction and crack development. The findings of this study will provide a better understanding of the placement behavior of multiple lifts of MFT and thus contribute to reclamation design standards and reduce the use of dedicated disposal areas.

关键词： Tailings Oil sand Environment Drying Multi-lift deposition

Swelling ability and behaviour of bentonite-based materials for deep repository engineered barrier systems:Influence of physical,chemical and thermal factors

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第3期14卷 689-702页

作者： Mohammed Alzamel mamadou fall Sada Haruna Department of Civil Engineering University of OttawaOttawaOntarioK1N 6N5Canada

Compacted bentonite-sand(B/S)mixtures have been used as a barrier material in engineered barrier systems(EBSs)of deep geological repositories(DGR)to store nuclear *** study investigates the individual and combined effects of different chemical compositions of deep groundwaters(chemical factor)at potential repository sites in Canada(the Trenton and Guelph regions in Ontario),heat generated in DGRs(thermal factor),dry densities and mass ratios of bentonite and sand mixtures(physical factors)on the swelling behavior and ability of bentonite-based *** this study,swelling tests are conducted on B/S mixtures with different B/S mix ratios(20/80 to 70/30),compacted at different dry densities(ρd=1.6-2 g/cm^(3)),saturated with different types of water(distilled water and simulated deep groundwater of Trenton and Guelph)and exposed to different temperatures(20℃-80℃).Moreover,scanning electron microscopy(SEM)analyses,mercury intrusion porosimetry(MIP)tests and X-ray diffractometry(XRD)analyses are carried out to evaluate the morphological,microstructural and mineralogical characteristics of the B/S *** test results indicate that the swelling potential of the B/S mixtures is significantly affected by these physical and chemical factors as well as the combined effects of the chemical and thermal factors.A significant decrease in the swelling capacity is observed when the B/S materials are exposed to the aforementioned groundwaters.A large decrease in the swelling capacity is observed for higher bentonite content in the ***,higher temperatures intensify the chemically-induced reduction of the swelling capacity of the B/S barrier *** decrease in the swelling capacity is caused by the chemical and/or microstructural changes of the *** results from this research will help engineers to design and build EBSs for DGRs with similar groundwater and thermal conditions.

关键词： Deep geological repository Engineered barrier Bentonite-sand materials Nuclear waste Swelling capacity Swelling strain

A multiphysics-viscoplastic cap model for simulating blast response of cemented tailings backfill

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第3期9卷 169-182页

作者： Gongda Lu mamadou fall Liang Cui Civil Engineering Department University of Ottawa Ottawa ON Canada

Although a large number of previous researches have significantly contributed to the understanding of the quasi-static mechanical behavior of cemented tailings backfill,an evolutive porous medium used in underground mine cavities,very few efforts have been made to improve the knowledge on its response under sudden dynamic loading during the curing *** fact,there is a great need for such information given that cemented backfill structures are often subjected to blast loadings due to mine *** this study,a coupled thermo-hydro-mechanical-chemical(THMC)-viscoplastic cap model is developed to describe the behavior of cementing mine backfill material under blast loading.A THMC model for cemented backfill is adopted to evaluate its behavior and evolution of its properties in curing processes with coupled thermal,hydraulic,mechanical and chemical ***,the model is coupled to a Perzyna type of viscoplastic model with a modified smooth surface cap envelope and a variable bulk modulus,in order to reasonably capture the nonlinear and rate-dependent behaviors of the cemented tailings backfill under blast *** of the parameters required for the variable-modulus viscoplastic cap model were obtained by applying the THMC model to reproducing evolution of cemented paste backfill(CPB)properties in the curing ***,the behavior of hydrating cemented backfill under high-rate impacts can be evaluated under any curing time of *** validation results of the proposed model indicate a good agreement between the experimental and the simulated *** authors believe that the proposed model will contribute to a better understanding of the performance of hydrating cemented backfill under blasting,and also to practical risk management of backfill structures associated with such a dynamic condition.

关键词： Thermo-hydro-mechanical-chemical (THMC) coupling Multiphysics processes Tailings Paste backfill Cap model Blast

Geotechnical characterization of peat-based landfill cover materials

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Journal of Rock Mechanics and Geotechnical Engineering 2016年第5期8卷 596-604页

作者： Afshin Khoshand mamadou fall Faculty of Engineering K.N.Toosi University of Technology Department of Civil Engineering University of Ottawa

Natural methane （CH4） oxidation that is carried out through the use of landfill covers （biocovers） is a promising method for reducing CH4 emissions from landfills. Previous studies on peat-based landfill covers have mainly focused on their biochemical properties （e.g. CH4 oxidation capacity）. However, the utilization of peat as a cover material also requires a solid understanding of its geotechnical properties （thermal, hydraulic, and mechanical）, which are critical to the performance of any biocover. Therefore, the objective of this context is to investigate and assess the geotechnical properties of peat-based cover materials （peat, peat–sand mixture）, including compaction, consolidation, and hydraulic and thermal conductivities. The studied materials show high compressibility to the increase of vertical stress, with compression index （Cc） values ranging from 0.16 to 0.358. The compressibility is a function of sand content such that the peat–sand mixture （1：3） has the lowest Cc value. Both the thermal and hydraulic conductivities are functions of moisture content, dry density, and sand content. The hydraulic conductivity varies from 1.74 × 10^-9 m/s to 7.35 × 10^-9 m/s, and increases with the increase in sand content. The thermal conductivity of the studied samples varies between 0.54 W/（m K） and 1.41 W/（m K） and it increases with the increases in moisture and sand contents. Increases in sand content generally increase the mechanical behavior of peat-based covers; however, they also cause relatively high hydraulic and thermal conductivities which are not favored properties for biocovers.

关键词： Landfill Geotechnical engineering Landfill cover Peat Compaction Compressibility Hydraulic and thermal conductivity

Air Pollution Related to Traffic and Chronic Respiratory Diseases (Asthma and COPD) in Africa

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Health 2017年第10期9卷 1378-1389页

作者： Fatou K. Sylla Adama Faye mamadou fall Anta TAL-DIA Institute of Health and Development-Public Health and Preventive Medecine Cheikh Anta Diop University (UCAD) Dakar Senegal Laboratory of Toxicology and Hydrology Cheikh Anta Diop University (UCAD) Dakar Senegal

Introduction: Chronic respiratory diseases (CRD) are obvious effects of air pollution and the third reason of death in developing countries. In Africa, air pollution from road traffic is one of the main causes of poor air quality. We set out to systematically review existing published researches on traffic related to air pollution and CRD, particularly asthma and Chronic Obstructive Pulmonary Disease (COPD) in Africa. Methods: A literature search of PubMed, Scholar and LISSA databases, published journals, reference articles, published up to 31 December 2016, has been done by using a research strategy procedure. Texts were reviewed for inclusion. Studies were included if they met the following criteria: 1) the relationship between asthma or COPD with ambient air pollution related to road traffic was studied and 2) the population included people from Africa or lived in Africa. Articles written in English and French were included. Results: Fifty-five articles were selected in this review, of which twenty-seven were on air pollution and CRD in Africa. The proximity of the residence or workplace to the traffic is associated with an increased risk of asthma with a dose-response relationship. The estimated prevalence of COPD varies between 2.7% and 38.5%. Conclusion: There is little research on traffic related to air pollution and CRD in Africa. Strategies to reduce traffic related to air pollution in African cities have been proposed in order to have a healthier ambient air.

关键词： Air Pollution Traffic Africa Asthma COPD

Traffic Air Pollution and Respiratory Health: A Cross-Sectional Study among Bus Drivers in Dakar (Senegal)

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Open Journal of Epidemiology 2018年第1期8卷 1-13页

作者： Fatou K. Sylla Adama Faye Mor Diaw mamadou fall Anta Tal-Dia Institute of Health and Development-Public Health and Preventive Medecine Cheikh Anta Diop University (UCAD) Dakar Senegal Laboratory of Physiology and Functional Explorations University of Cheikh Anta Diop Dakar Senegal Laboratory of Toxicology and Hydrology Cheikh Anta Diop University (UCAD) Dakar Senegal

Introduction: Road traffic exposes bus drivers to the detrimental effects of air pollutants on respiratory health. This study determined the frequency of chronic respiratory illnesses and its related factors among bus drivers in Dakar, Senegal. Methods: This study had a cross-sectional design conducted in a total of 178 bus drivers in Dakar, Senegal. A questionnaire was used to inquire about socio-economic characteristics, occupational factors and respiratory symptoms of bus drivers. Lung function tests were used to determine the presence of asthma and Chronic Obstructive Pulmonary Disease (COPD). The relationship between our variables of interest and respiratory diseases was determined by logistic regression analysis. Results: The results of the study show that 57.9% of bus drivers had a chronic cough, and 65.7% had recurrent cold. Lung function tests showed that 38.8% of bus drivers had asthma and 30.3% COPD. Multivariate analysis found that recurrent cold increased the risk of asthma (OR = 6.3, 95% CI: 1.12 - 35.79) and COPD (OR = 7.7, 95% CI: 1.14 - 52.8). The respiratory health status of bus drivers depended on the work area (OR = 3.2, 95% CI: 1.13 - 9.31). Conclusion: The respiratory symptoms and illnesses observed among bus drivers are associated with their exposure to air pollutants from road traffic.

关键词： Air Pollution Bus Drivers Asthma COPD Senegal

Mineralogical Characterisation of the Sedimentary Phosphate Deposit of Tobene （Western Senegal）

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Journal of Shipping and Ocean Engineering 2016年第4期6卷 226-240页

作者： Moustapha Diagne mamadou fall Mouhamadou Bachir Diouf Ndeye Penda Dione El Hadji MansourSamb Department of Geology Faculty of Science and Technology Cheikh Anta Diop University Dakar - Senegal Chemical Industries of Senegal

The Tobrne panel is the third of the Ta＇fba phosphate deposit. This mineralogical study contributes to the improved knowledge of the various facies that comprise the phosphate series of Tobrne. Based on X-ray diffraction results, the Tobrne panel yielded minerals that are primarily divided into four groups： minerals of the original phosphate phase： apatite, fluorapatite; carbonate minerals： calcite and dolomite; clay minerals： palygorskite, smectite, kaolinite and illite; minerals of altered facies： alteration minerals （analcime, millisite, crandallite and wavellite） and ferruginous minerals （goethite and gibbsite）. This succession of mineralogical associations reflects a polyphase alteration leading to a vertical and lateral facies sequence. This alteration intensifies the phosphate series upward and laterally from West to East.

关键词： Tobene Taiba phosphate mineralogy Western Senegal.

Health Risk Assessment of Trace Metals in Drinking Water Consumed in Dakar, Senegal

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Journal of Water Resource and Protection 2021年第12期13卷 915-930页

作者： Jessica Carmelia Mbemba Peleka Cheikh Diop Robert Faomowe Foko Mouhamadou Lamine Daffe mamadou fall Laboratory of Toxicology and Hydrology (LTH) Department of Pharmacy Faculty of Medicine Pharmacy and Dentistry (FMPO) Cheikh Anta Diop University (UCAD) Dakar Senegal

Water contamination by chemical pollutants is increasingly associated with waterborne diseases worldwide. The objective of this study is to assess the chemical health risk associated with drinking water consumption in Dakar, Senegal. The methodology adopted in this study is based on the determination of trace metals (Cd, Pb, Fe, Cu and Mn) in human drinking water by flame atomic absorption spectrometry, the estimation of the exposure of populations of the study area on the basis of the quantity of water consumed daily and the determination of the hazard quotient which allows estimating the health risk. The results indicate unacceptable levels of Pb and Cd in the water according to World Health Organization (WHO) guidelines, while the concentrations of Fe, Cu and Mn are below the regulatory values. The hazard quotient (HQ) is in the majority of samples higher than 1 in children and infants for scenario 1 (based on WHO data), reflecting a high risk for this target. In scenario 2 based on consumption data from the populations studied, the HQ is greater than 1 only in heavy consumers. The drinking water consumed by Dakar population presents health risks related to Pb and Cd, particularly for infants, children and heavy consumers, hence the need to strengthen the water treatment system before home consumption.

关键词： Drinking Water Trace Metals Health Risk Senegal