| 1. |
- Al-Jabban, Wathiq Jasim
(författare)
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Soil Modification by adding small amounts of binders : A laboratory study
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soil stabilization through addition of a hydraulic binder is a method frequently used to modify and improve engineering properties of soft soils. Additives like cement and lime are typically used as stabilizers. More recently, industrial by-products, such as fly ashes, cement kiln dust, blast furnace slags and other slags have been used. The chemical reaction between the soil and the stabilizer alters the physical and engineering properties of the soil and thus desired strength and durability are obtained. The choice of appropriate type and quantity of stabilizer (binder) depends largely on factors such as soil type, moisture content, organic content, sulfate content, curing conditions (time and temperature) and the desired improvement.The objective of this thesis is to increase knowledge and understanding of how small amounts of binders change various engineering properties of stabilized soils in short- and longtime perspective. Extensive laboratory and field programs have been carried out. They cover immediate and long-term effects on the engineering properties by adding various binders. Cement, Multicem, and by-products Petrit T and Mesa were used as binders. Binder was added to the soil at various quantities: 1%, 2%, 4%, 7% and 8% of soil dry weight. The field and laboratory investigation included tests of consistency limits, sieving and hydrometer, unconfined compressive strength, density, solidification, grain size distribution using laser particle size analyzer, leaching tests and pH value. The tests were carried out on the treated soil with different binder contents and after different curing times i.e. 7, 14, 28, 60, 90 days for laboratory tests and 7 and 35 days for field investigation.The unconfined compression tests were used to show the effects of different binders on the enhancement in strength and stiffness over time. Consistency limits were determined to investigate the effects of the binders on the consistency limits, directly after treatment and over time. Laser particle size analyzer tests were conducted to investigate the effects of different binders on the particle size distribution (PSD) before and after treatment. The pH tests were conducted to investigate the effects of different binders on the alkalinity of the soil immediately after treatment and over time. This was used to give an indication of soil-binder reactions. MRM leaching tests were conducted to investigate the acidification potential of soils before and after treatment. Freeze-thaw cycles were conducted to investigate the strength characteristics after freezing and thawing in short- and long-term perspectives. Visual observation and standard dry sieving tests were conducted to optimize the proper mixing times to disintegrate or homogenize the soils by decreasing the size of agglomerated soil particles.The results show, that the variation in soil strength and stiffness of the treated soils are linked to different chemical reactions. Cement is most effective in improving the physical and engineering properties compared to the other binders studied. The plasticity index of soil decreases after treatment and over time. Liquidity index and the ratio of water content to plastic limit are introduced as new indices to illustrate the improvement in workability of treated soil by measuring the reduction in the liquidity index. This is found directly after treatment and it increases with time when the liquidity index is within the plastic range or when the water/plastic vi limit ratio is more than one. Increase of binder content and using longer curing times result in increase of soil density and decrease of water content. Particle size distribution of soil is changed by reducing the clay size fraction and increasing the silt size particles after treatment. This shows that an aggregation of particles take place resulting in coarser material than the initial. The cement-treated soils exhibit a more brittle failure in the unconfined compression tests compared to soils treated with other binder types where a more ductile behavior is observed. Applying freezing-thawing-cycles reduces the strength and stiffness of the treated soil.The appropriate length of time to homogenize and disintegrate the natural soil prior to treatment depends on several factors, such as soil type, water content, and plasticity properties of soil. For high plasticity soil, the disintegration time should be kept as short as possible. The homogenizing and disintegration time is less important for low plasticity soils with low water content than for medium to high plasticity soils.The acidification potential of soils are related to the addition of cementitious binders. The effect is found directly after treatment and over time. The treated soil exhibits higher resistance to decrease in pH value. The strength and stiffness properties found in the field investigation agree in general with those obtained from the laboratory investigation for the same binder type.
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| 2. |
- Al-Madhlom, Qais
(författare)
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Potential Use of Aquifer Thermal Energy Storage System in Arid Regions
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After the Oil Crises in 1973, which meant higher energy costs, the world started to look for other sources of energy. This led to the development of renewable energy techniques. Because of the intermittent nature of renewable energy, storage systems were also developed. Underground Thermal Energy Storage (UTES) systems spread and are now globally well known. In these systems, excess thermal energy (heat or cold) is stored (short term and/or long term) from the surplus period to periods of higher demand. The storage media in such systems are underground materials, e.g. rock, soil, and/or groundwater. The current study aims to examine the use of underground thermal energy storage systems in arid regions, in order to increase the efficiency of both cooling and heating systems in these regions, such that CO2 emissions and consumed electricity for these purposes are reduced. Three main parameters determine which type of Underground Thermal Energy Storage (UTES) systemis most suitable. These are site, design, and operation parameters. The site-specific parametersinclude soil properties and all geo-hydrological, environmental, geological, metrologicalconditions. Therefore, the site parameters cannot be changed after installing the storage system,since they majorly depend on the location, while the other parameters (design and operation) canbe changed after construction. The first primary goal of this study is to find how and what site parameters involved to specify the most suitable type of UTES systems in arid regions. Thus, the suitable type of UTES systems can be decided. The second primary goal is to answer how and where to select the best location to install the adopted system. To achieve the goals of the study, two arid regions within Iraq were used as case studies. They are Babylon and Karbala, where the former is characterized by its shallow aquifer, while the latter is characterized by a relatively deeper aquifer. The ArcMap-GIS software was used to prepare the relevant digital maps, e.g. maps of hydraulic conductivity, population, type of soil, aquifers, groundwater elevation, transmissivity, and slope. Then, the vulnerability (readiness for being polluted by the surface contaminants) maps of the available aquifers were determined, followed by finding the seepage velocity of the groundwater. Depending on the outputs of the vulnerability and the seepage velocity, the most suitable type of Underground Thermal Energy Storage (UTES) systems can be decided. This study, also, includes developing/inventing a general methodology that can be used to determine the best location to install Underground Thermal Energy Storage (UTES) systems, including Aquifer Thermal Energy Storage (ATES) systems. The last part of this study includes applying the suggested methodology to determine the best location to install the suitable type of Underground Thermal Energy Storage (UTES) system in the study area. The first study was in the Babylon Province. Here, groundwater table is very shallow (less than 2 m depth in some regions). The crystalline bedrock is at a depth of 9-12 km below the ground surface, overlaid by 9-12 km of sedimentary rocks on which there is a 2-50 m thick layer of alluvial silty clay sediments. The groundwater moves slowly in this aquifer (2.12*10-6 - 1.85*10-1) m/d, and it is brackish having salinity of 5000-10000 mg/l. The susceptibility (vulnerability) of the aquifer in northern part of Babylon province is low to very low having ranges from 80 to 120 on Drastic model scale, which has the overall range of 26 – 226 (i.e. 0.27- 0.47 on normalized vulnerability). The second study area was a part of Karbala Province. This area can be divided into two regions based on the geology and geo-hydrological conditions. An eastern part is located on the Mesopotamian plain, and a western part is located in Western Desert. In both parts, the groundwater table is relatively deeper than the Babylon province. In the eastern part, it is generally more than 4 mbgs (meter below ground surface). While, in the western part it is deeper and reaches to 48 mbgs in depth. The soil in the eastern part is alluvial silty clay, while the western part consists of gypcrete sandy deposits. The groundwater, which flows towards the east, has a seepage velocity range from 0 to 0.27 m/d. The salinity of the groundwater changes from slightly brackish (1000-3000) mg/l in the western parts to highly brackish (5000-10000) mg/l in the Mesopotamian parts of the province. By comparing the site parameters of each province with the different UTES systems, the type of thermal energy storage system was decided. The most important site parameters are the depth of the water table and the aquifer characteristics. For Babylon Province, the expected suitable underground thermal energy storage system is an aquifer thermal energy storage system in silty clay. For Karbala Province, two systems are suggested: for the eastern part, aquifer thermal energy storage system in silty clay is recommended, while for the western part, a deep (10-30 m depth) sandy aquifer thermal energy storage system is recommended. After that, a methodology was developed and used to determine the suitable location in which to install the Aquifer Thermal Energy Storage (ATES) system. For Babylon province, the site selection index ranges between 2.9 and 5.3 on 1 to 10 scale. About 71% of the region has a site selection index ranges between 4.71 and 5.3. Concerning Karbala study area, the site selection index ranges between 3.1 and 9.1. About 15% of the region has a site selection index between 8.1 and 9.1.The energy saving in neighboring countries to Iraq by using the Aquifer Thermal Energy Storage (ATES) system ranges from 55% to 72%. It is also expected that using a ground sink heat pump instead of a conventional air-to-air heat pump increases the COP (Coefficient Of Performance) of roughly (10) to (-17). The negative sign means that the heat is injected into the ground. More theoretical and field studies are required to cover the different aspects of the subject of potential use of Aquifer Thermal Energy Storage (ATES) system in an arid region, and to verify the improvement of COP (Coefficient Of Performance) due to using these systems.
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| 3. |
- Chabuk, Ali
(författare)
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Solid Waste Landfills in an Arid Environment : Site Selection and Design
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Selecting landfill sites is considered a complicated task because its whole process is based upon several factors and restrictions. This study shows the present status of solid waste management, sources, collection personnel, machinery and equipment that are involved in the waste collection process, financing and financial management for the major cities of the Babylon Governorate in Iraq (Al-Hillah, Al-Qasim, Al-Mahawil, Al-Hashimiyah and Al-Musayiab). The management of waste collection and disposal in the Babylon Governorate and its districts is through open waste dumps, so the quality of the collection and disposal process is poor, and these sites do not conform to the scientific and environmental criteria usually applied in the selection of landfill sites.In the first part of the current study, three methods were used to calculate the solid waste quantity for each specific year up to the year 2030 as well as the cumulative quantity of solid waste for the period (2020-2030) for Babylon Governorate. The results show the cumulative quantity of solid waste resulting from (method 3) receives a high value compared to other methods, and so it is used as a maximum value to estimate the required area for candidate sites for landfills in each district. The generation rate in 2030 will be (0.97, 0.69, 0.48, 0.62 and 0.91) (kg/capita/day) in (Al-Hillah, Al-Qasim, Al-Mahawil, Al-Hashimiyah and Al-Musayiab), respectively, based on method 3, where the estimated annual incremental generation rate is 1 %. The second part of this study aims to find the best sites for landfills in the arid areas that are distinguished by a shallow depth of groundwater. The Babylon Governorate was selected as a case study because it is located in an arid area, and the depths beneath the ground surface to the groundwater level are shallow. For this purpose, 15 important criteria were adopted as follows: groundwater depth, rivers, soil types, agricultural land use, land use, elevation, slope, gas pipelines, oil pipelines, power lines, roads, railways, urban centers, villages and archaeological sites. These criteria were then entered into the geographic information system (GIS). The GIS software has a large capacity to manage and analyze various input data using special analysis tools. In addition, Multi-Criteria Decision Making (MCDM) methods were used to derive the relative weightings for each criterion in different styles. These methods are (Analytical Hierarchy Process (AHP), Simple Additive Weighting (SAW), Ratio Scale Weighting (RSW) and Straight Rank Sum (SRS)).Raster maps of the selected criteria were prepared and analyzed within the GIS software. The final map for candidate landfill sites was obtained through combining the GIS software and (MCDM) methods. Subsequently, comparison methods (Change Detection, Combination, Kappa and Overall Assessment) for each pair of raster maps that result from using the two different methods of multi-criteria decision making were implemented to determine the pixel percentage of matching and non-matching as well as to determine and check the suitability of the selected sites for landfills on both resulting maps using two methods. Two suitable candidate sites for landfills were determined to fulfill the scientific and environmental requirements in each major city. These areas are (6.768 and 8.204) km2 in Al-Hillah, (2.766 and 2.055) km2 in Al-Qasim, (1.288 and 1.374) km2 in Al-Hashimiyah, (2.950 and 2.218) km2 in Al-Mahawil, and (7.965 and 5.952) km2 in Al-Musayiab. The required area of the selected sites can accommodate solid waste from 2020 until 2030 based on the required areas according to the third method.The third part of this study includes soil investigations for the selected landfill sites. The suggested design should ensure that there is no groundwater pollution by leachate from these sites because the groundwater depth is very shallow in the Babylon Governorate. To avoid this problem, soil investigation was conducted at these sites so that the most suitable landfill design could be established. Each site was subjected to field soil tests to find the composition of the soil strata at each site to a depth of 10 m, and these results were compared with the soil properties adopted for final site selection. The Iraqi Ministry of Housing & Construction, National Centre for Construction Laboratories and Research Babylon, Iraq, carried out the analytical work on the soil in 2016. The results of the soil investigation at these sites include the soil profile, groundwater depth, chemical properties, allowable bearing capacity, atterberg limits test results and material characteristics of the soil strata. According to the results of these tests, the best design is the one that puts the compacted waste at the surface.The fourth part of this study covers the selection of a suitable proposed design in the arid areas (Babylon Governorate, Iraq) for the selected landfill siting. In the current study, the design of this landfill includes the suggested soil layers for the liner system and final cover system. For the base liner system (from the bottom toward the top), the composite bottom barrier layer consists of highly compacted sandy clay. The thickness of the bottom barrier layer is 60 cm, and its saturated hydraulic conductivity is 1.0E-7cm/s. The 1.5 mm thick geomembrane (HDPE), with hydraulic conductivity of 2.0E-13 cm/s, is placed over the composite bottom barrier layer. The leachate collection system consists of drainage layer (gravel) with a thickness of 30 cm and a hydraulic conductivity of 3.0E-1 cm/s. The diameter of the main drainpipes is between 15 and 20 cm. The protection layer consists of sand material, and its hydraulic conductivity is 5.0E-3 cm/s. The thickness of the protection layer is 30 cm.The compacted solid waste is placed upon the surface to a height of 2 m because of the shallow groundwater depth and to avoid groundwater contamination by leachate from the landfill site. The density of the compacted waste is 700 kg/m3, and its saturated hydraulic conductivity is 1.0E-5 cm/s.Three scenarios were used for the suggested designs for the final cover system of the landfills in arid areas. The first scenario was “evapotranspiration soil cover (ET) (capillary barriers type)”, the second scenario was a modified cover design of "RCRA Subtitle D", and the third scenario was the “Recommended design”. In this study, “Recommended design”, the third scenario for the final cover system, was adopted in the arid area (Babylon governorate, Iraq) based on combining certain layers from the first and second scenarios. For the three scenarios, the soil components in these designs used was based on available local materials in the study area. The layers of the base liner system were adopted in all scenarios.The third scenario for the final cover system, “Recommended design”, was implemented based on weather parameters in the arid areas. The water infiltrated from the surface of landfill is stored within upper layers that have fine particles. This allows the stored water to evaporate from the soil surface of the landfill or transpire through vegetation due to the high temperature during most months in the study area. The water that enters from the surface of the landfill should be contained above the geomembrane liner and top barrier layer without leakage into the waste body, thereby preventing leachate generation.For the layers of the final cover system (from the bottom to the top), the intermediate cover is used to cover the waste body, and this layer consists of moderate compacted silty clayey loam (native soil). The thickness of the intermediate cover is 30 cm, and its saturated hydraulic conductivity is1.0E-6 cm/s. The foundation layer consists of coarse sand material with a thickness of 30 cm and a saturated hydraulic conductivity of 1.0E-2 cm/s. This layer acts as a cushion for the layers of the final cover system. The gas collection system can be installed within the foundation layer. The top barrier layer is placed over the foundation layer. This layer consists of highly compacted sandy clay of (45 - 60 cm) thickness with compacted lifts (each lift is 15 cm). The saturated hydraulic conductivity of the barrier layer is 1.0E-7 cm/s. The geomembrane liner, (HDPE) of 0.5 cm thickness and a saturated hydraulic conductivity of 2.0E-13 cm/s, is put on top of the barrier layer. The upper layers of the final cover system are the support vegetation layer and the topsoil layer. The composition of the support vegetation layer is moderate compacted loam. This layer is placed directly on the geomembrane liner. The saturated hydraulic conductivity of the support layer is1.0E-5 cm/s, and its thickness is 45 cm. The topsoil layer consists of silty clayey loam, and it is placed over the support vegetation layer with a slope of 3%. The thickness of the topsoil layer is 15 cm, and its hydraulic conductivity is 4.0E-5 cm/s. The Hydrologic Evaluation of a Landfill Performance (HELP 3.95 D) model was applied to the selected landfill sites in the governorate to check if there could be any infiltration of the leachate that will result from the waste in the landfills in the selected sites in the future. The HELP model, which utilizes both weather and soil data, is the most commonly used model for landfill design, and it is employed to evaluate the quantity of water inflow through soil layers for the designed landfill. This suggested landfill is designed using the weather parameters (rainfall, temperature, solar, and the required date to calculate evapotranspiration) for the 12 consecutive years from 2005 to 2016, as well the required data for soil design.In the HELP model, the result for the suggested landfill design for both the recommended design (third scenario) and the second scenario was a modified cover design of "RCRA Subtitle D", which showed there was no leachate through the soil
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| 4. |
- Do, Tan Manh
(författare)
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Excess pore water pressure generation in crushed and fine granular materials under cyclic traffic loads
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Excess pore water pressure can develop in subgrades of railway and pavement substructures due to cyclic loading from heavy traffic, leading to the migration of fine particles into upper layers. This migration can clog pores and diminish the drainage capacity of upper layers,negatively impacting the long-term performance of sub-structures and service life, ultimately risking failure. Therefore, understanding the mechanisms behind the accumulation of excess pore water pressures and the migration of fine particles under cyclic loading is essential for efficient and cost-effective maintenance methods. The main objectives of this research include (1) investigating excess pore water pressure generation in crushed and fine granular materials under cyclic loading, (2) evaluating the migration of these materials into upper layers under cyclic loading, and (3) simulating a practical application using an advanced model to provide valuable insights into the operation of structures subjected to cyclic traffic loads while considering real-world factors from the field.A series of cyclic triaxial tests were conducted to investigate the generation of excess pore water pressure in fine granular materials. Two types of fine granular materials, tailings (a crushed material) and railway sand (a fine granular material) were selected for this investigation. The cyclic characteristics of these materials, including cyclic axial strain and excess pore water pressure, were evaluated in terms of number of cycles and applied cyclics tress ratios (CSR). As a result, the cyclic axial strain and excess pore water pressure were observed to accumulate over time due to cyclic loading. However, the extent of accumulation was found to be significantly dependent on CSR values and material types. In addition, a relationship between excess pore water pressure and cyclic axial strain of the fine granular materials was established and proposed based on the results from the undrained cyclic triaxial tests (including both tailings and railway sand samples).To assess the migration of fine granular materials into overlying layers under cyclic loading, a modified large-scale triaxial system was employed as a physical model test. A quantitative analysis of material migration was based on the mass percentage and grain size of migrated materials collected at the gravel layer. Additionally, cyclic responses (strain and excess pore water pressure) were evaluated. As a result, the total migration rate of the tailing sample was significantly higher than that of the railway sand sample. The migration analysis on tailings also revealed that finer tailings particles exhibited a greater tendency to migrate into the upper gravel layer compared to coarser tailings particles under cyclic loading. This migration could be attributed to significant increases in excess pore water pressure during the final cycles of the physical model test. The findings from this research could make a valuable contribution to the existing literature concerning the accumulation of excess pore water pressure and its effects on the migration of fine particles under cyclic loading.A numerical study was conducted to simulate the complex interactions between tailings materials and cyclic traffic loads on the piers of tailings dams. The integration of experimental data and advanced constitutive models enabled a comprehensive understanding of the behavior of tailings under these loading conditions. The findings focused on the build-up of excess pore water pressures in tailings subjected to cyclic traffic loads while taking into account the effects of truck loads, velocities, and truck resting times. As a result, excess pore water pressures in tailings progressively increased with the number of passing trucks, indicating a cumulative effect of loading cycles. In addition, the effect of truck loads and truck velocities on the excess pore pressure build-up was discovered, with higher truck loads and lower truck velocities leading to increased excess pore pressures, posing a greater risk. Furthermore, through anoptimization process involving variations in truck loads, velocities, and resting times, it was revealed that a combination of increased truck velocity, reduced truck load, and extended truck resting time could effectively minimize the build-up of excess pore water pressures in tailings beneath the pier. These findings offer valuable guidance for optimizing transportation operations on tailings dam piers, enhancing efficiency and safety.
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| 5. |
- Ezz-Aldeen Mohammad, Mohammad
(författare)
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Sedimentation and Its Challenge for Sustainability of Hydraulic Structures : A Case Study of Mosul Dam Pumping Station
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A successful management and operation of water resources projects are essential to maintain their functions. Dams and reservoirs are one of the largest worldwide infrastructures. They serve one or more functions; reliable store and release of water for different purposes, hydropower generation and flood and draught controls. Sedimentation is one of the serious problems that affects the reservoir`s efficiency; it leads to reduction in storage capacity and reliability for water supply. Furthermore, deposition of sediment near and inside the intakes and hydropower plants cause a negative effect on plant efficiency and corrosion of turbines and pump`s impeller. Generally, degradations of the watersheds, surface runoff and river flow are the main sources and transporters of the reservoir’s sediment. Sediment management techniques are the most economical and efficient approach for sustainability of reservoirs and attached structures. Pumping rate, operation schedule, sub watersheds sediment control and earth dike is the reasonable alternatives that were applied in this study for sediment control and sustain water intakes. In Mosul Dam reservoir, the pumping station is considered as a case study, the station is suffering from sediment accumulation in front and inside the intake. The work includes application of Soil and Water Assessment Tool (SWAT) models to estimate the runoff and sediment load delivered by sub watersheds surrounding the studied area, and a sediment rating curve was considered to assess the sediment load carried by the main river (Tigris River). The Hydrological Engineering Centre’s River Analysis System ( HEC-RAS) model as a one dimensional model (1-D) was applied for sediment routing, and as a two dimensional model (2-D) for flow analysis. This aims to estimate the sediment load deposited in the studied reservoir and evaluated the effects of pumping rate and flow depth on flow velocity distribution, flow stream power and sediment transport. As this study focuses on the sedimentation problem on the area around the intake’s structure and due to compound flow regime and sediment transport near the intakes and withdraws outlets, a three dimensional (3-D) model is considered more suitable than a 1-D or a 2-D model. The Sediment Simulation in Intakes with Multiblock option (SSIIM) model was considered also in this study; a proper control code for studied case was developed. This model depends on Computational Fluid Dynamics (CDF) techniques as a numerical method to solve fluid motion problems.The applied models were calibrated and validated based on measured data of previous studies. The considered statistical criteria indicate that the models’ performances were reasonable for both flow and sediment assessments. The results of all applied strategies show an improvement with a different percent in the amount of sediment deposited in front and inside of the intake, in comparison with the current situation. The optimal improvement was obtained by adding a control earth dike upstream the station. It is considered the most efficient and practical strategy that can be applied for sustainability of the pumping station efficiency and lifespan with fewer dredging requirements.
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| 6. |
- Knutsson, Roger, 1987-
(författare)
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On the behaviour of tailings dams : Management in cold regions
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Associated to mining activities there is mine waste generated. The residues left over from mineralextraction processes are referred to as tailings, normally stored in surface tailings facilities. Thefacilities are usually confined by embankment dams, so called tailings dams. Sufficient stability of thetailings dams is essential, and a proper management of the tailings is needed in order to maintain asafe storage. However, optimal strategies for tailings management are very much site specific, andthere is no universal answer on how tailings management should be applied. Despite the availableguidelines, recommendations and current trends in the industry on how to handle tailings, theremust be a pertinent approach to optimize tailings management to the site-specific conditions.The aim with the work presented in this thesis is to enhance current practice in tailings managementin cold regions. Three sets of research objectives are presented, from which recommendations will begiven on how management can be adjusted for site-specific conditions.Firstly, depositional aspects in cold climate are studied. A methodology is proposed where thethermal regime is studied in a tailings facility with active deposition, i.e. raised tailings surface, andconcurrent freezing and thawing. Despite the fact that there is no natural permafrost in Sweden, thedeposition can imply generation of “man-made” permafrost in the facilities. The model is simple andeasily accessible data are used as input. With a proposed methodology, deposition schedules can bemodelled, and the deposition scheme can be adjusted in order to prevent permafrost generation intailings facilities.In addition to the depositional aspects in cold climate, a study is presented focusing on thaw stabilityof tailings beach slopes. The tailings beach is the inclined surface of settled tailings without pondedwater. For conventional tailings deposition, the beach slopes are relatively flat and the need for thawstability analyses is trivial. However, there is a current trend of adopting thickened tailingstechnology where steeper beach slopes are one of the intended merits. The increased slopeinclination might be unstable with major seasonal freezing and thawing. In rapid thaw excess porewater pressure might be generated, creating instability where masses of tailings can slide along a stillfrozen interface. Increased storage capacity, or freeboard, along the surrounding dams might beneeded, and the intended merits with the thickened tailings technology might be lost.Secondly, a study on the determination of strength parameters on granular soil is presented. Simpleshear tests are widely used particularly in Sweden for soil strength determination. However, recentstudies on tailings indicate large differences on the evaluated strength compared to what isdetermined via triaxial testing. In this thesis a laboratory study is presented, where simple sheartesting and triaxial testing were conducted. The results were used for examining the Swedishguidelines on simple shear testing and associated strength determination. It was found that directapplication of strength determined by simple shear testing leads to incorrect design assumptions.Thirdly, a study on prediction and verification of tailings dam stability is presented. Dam stability iscentral in tailings management, and a convenient way to describe the safety is via the factor of safety(FoS). Although the FoS can be predicted via calculations, it cannot be measured directly in the field.Therefore, in order to verify the calculated stability, field measurements must be used to comparewith the anticipated performance. With good agreement the prediction indicate reliableunderstanding of the dam, and the predicted stability can be verified. Without good agreement, thestability is easily questioned.Based on findings from the three sections presented in the thesis, recommendations are given ontailings management in cold regions. With increased knowledge in the field of tailings deposition incold climate, shear parameter determination and overall dam stability assessment, current practice intailings management is enhanced.
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| 7. |
- Lagerlund, Johan
(författare)
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Grout Development and Methods for Remedial Grouting of Embankment Dams
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An embankment dam can be damaged by internal erosion. During this process, the soil material erodes and is transported out of the dam structure. Some common types of damage due to internal erosion are piping, less dense soil zones, and zones where the fine material has been washed out.To prevent ongoing internal erosion from developing into a damage or a breach, injection grouting may be performed to replace the eroded soil material. In an embankment dam, injection grouting is usually performed vertically. A pipeline is drilled from the crest of the dam to the damaged zone, to which the grout material is delivered via a pump. The injection grouting methods suitable for embankment dams are compaction and permeation grouting. In compaction grouting, a lowmobility grout material is injected at high pressure, compacting the surrounding soil. In permeation grouting, the injection pressure is lower and the grout material flows more easily, allowing it to permeate the porous structure of the soil into which it is injected.A grout material for embankment dams should have properties, i.e., particle size distribution, water content, shear strength, and bulk density, similar to those of the original core soil after injection. A grout material with these properties will however be very stiff and difficult to pump, and permeation will be difficult to achieve. Therefore, a new type of non-hardening grout material has been developed and tested in the laboratory. The grout material is a low-mobility grout, but its viscosity and yield strength can be temporarily lowered by replacing the fine aggregates with a limestone filler and by adding a superplasticizer. After injection, the effect of the superplasticizer wears off, leaving a grouted zone with geotechnical characteristics similar to those of the original core soil. The grout material consists of 0–4 mm aggregates, limestone filler, dry bentonite powder, water, superplasticizer, and an air-release agent. The grout material properties and the influence of injection method were tested in three laboratory investigations and the results were presented in four papers.Development, and fresh and hardened properties of the grout material were investigated in Paper I. The key findings are: (1) The grout material attracted air when homogenized. When homogenized longer than 15 minutes, it was difficult to pump. Air content up to 16.5 % was observed. (2) After 34 days of storage, the water content was ~10 % and the bulk density ~2250 kg/m3, which are very similar to those of the core soil. The undrained shear strength was ~13 kPa, which was initially lower than that of the core soil but it slowly increased with time.The factors affecting a grout material’s ability to permeate a core soil damaged by internal erosion were investigated in a pilot-scale permeation test series and the results are presented in Paper II. Three different coarse-grained materials with d15of 35, 75, and 110 mm were grouted. The key findings are: (1) The ratio between limestone filler and aggregates in the grout material greatly influenced the permeation. A grout material with a ratio of 1.7 performed far better than a grout material with a ratio of 1.4. (2) A higher consistency measurement of the groutmaterial (150 mm vs. 100 mm) improved the permeation if low injection pressure was used. At higher pressure, the role of consistency was minor. (3) A higher maximum particle size, Dmax, of the grout material (4 mm compared to 2 mm) improved the permeation. The difference was most probably caused by higher viscosity and higher yield strength of the grout material with Dmax = 2 mm compared to that with Dmax = 4 mm. The lowest ratio between the minimum particle size of the coarse-grained material and the maximum particle size of the grout material was 4, and using higher pressure, the grouting was successful. Ratios below 4 were not tested.From Paper II, the most suitable materials for permeation grouting were chosen to be investigated further for their resistance to flow. The results of this investigation were presented in Paper III. Resistance to flow in the pilot-scale permeation test was found to occur within the pipeline and at its exit, where the grout material downflow was redirected 180° to an upward flow. Total frictional losses could be estimated by regarding the grout material flow as Newtonian laminar. Total frictional losses in the 1.3 m length and 0.075 m diameter pipeline during all testswere measured to be 1–67 kPa/m at grout material velocity of 0.01–1.03 m/s. Frictional losses due to the grout material’s permeation of the coarse-grained materials could be estimated with the hydraulic conductivity. The mean hydraulic conductivities in the d15 = 75 mm coarse-grained material, when permeated by the Dmax = 2 mm and 4 mm grout materials, were measured to be 1.7x10-4 and 1.4x10-4m/s, respectively; where as in d15 = 110 mm, the values were 2.1x10-4 and 3.3x10-4m/s. These observed values of the hydraulic conductivity were very close to the expected values. With the Newtonian approach, pressure losses may be easily estimated. This will facilitate the estimation of how much of the grouting pressure at the pump is transferred into the core soil during a grouting operation. The possibility to quantify pressure losses during the permeation of the coarse-grained material with hydraulic conductivities can be used when estimating permeation depths vis-à-vis applied injection pressure.The method, “Identification – Localization – Characterization – Remediation”, was tested at the abutment of a large-scale test embankment dam with the newly developed grout material and presented in Paper IV. The seepage rate was successfully reduced to 40 % directly after the injection grouting, and up to 70 % after one year. Most of the seepage reduction was caused by the rotary percussion drilling. Remedial grouting should not be regarded as a last resort, but as a part of a maintenance program.
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| 9. |
- Nigéus, Susanne
(författare)
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Recycling of green liquor dregs in cover application on acid generating mine waste
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mining industry generates massive amounts of waste that without treatment and in contact with atmospheric oxygen can cause the formation of acid rock drainage (ARD). In Sweden, the most common reclamation measure for mine waste is to apply a multi-layer cover on top of the waste deposit. The access to suitable cover-materials is, however, limited and can lead to extensive costs for the mining companies. This creates a driving force for alternative solutions, e.g., bentonite amendment to till. As bentonite production is costly both economically and environmentally, recycling of industrial residues to produce sealing layer material is an attractive option. The recycling is beneficial for the industry generating the residue, the mining industry using the residue and the society in its strive for zero waste. An industrial residue that has potential to improve the sealing properties of local till is green liquor dregs (GLD), a residue from pulp production. The main objective of this study was to, by laboratory studies and field application and evaluations, investigate if green liquor dregs amended till can be used as a sealing layer material on top of acid generating mine waste. The conclusion from the laboratory study is that the hydraulic conductivity does not decrease significantly with GLD addition to the silty till. However, the water retention capacity, which can be seen as the major important feature of a sealing layer to be used on top of sulfidic mine waste by keeping the layer close to saturation, shows significant improvements with GLD addition. In the field study the GLD amended till was applied successfully from a soil mechanical point of view (e.g., the compaction degree after application). The early results from the monitoring of the sealing layer indicate results comparable to the more frequently used bentonite amendment in a sealing layer, with soil moisture values reaching close to saturation. However, this study also concludes that the great variation in GLD, especially regarding its soil mechanical properties such as water content, makes it difficult to use compared to commercial products. The material used in the laboratory investigations in the planning phase of a project might behave differently than the one that is delivered to the minesite for reclamation.
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- Silva, Ingrid, 1988-
(författare)
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Investigation of Suffusion in Glacial Till Dam Cores : Testing methods and critical hydraulic gradients
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Suffusion is an internal erosion mechanism that occurs in embankment dams when fine grained particles in the dam core are washed out by seepage. Initiation of internal erosion depends mainly on three major factors: grain size distribution of the soil, stress conditions and hydraulic gradient; whilst its continuation depends on the properties of the filter. Broadly graded moraines, as glacial tills, are more susceptible to internal erosion by suffusion than other types of soils used in dams. Most embankment dams in Sweden consist of a central core of glacial till built more than 50 years ago. At the time of its construction, the available guidelines did not include specific grain size boundaries for the core and the filter related to internal erosion susceptibility. Today, several Swedish embankment dams have experienced incidents of internal erosion such as leakages and sinkholes, making internal erosion an important safety issue. This circumstance leaded to the question: what are the conditions triggering internal erosion by suffusion in embankment dams? This research aims to contribute to the assessment of dam safety by increasing the knowledge on glacial till soils regarding: i) the optimum empirical method to evaluate the susceptibility to suffusion; ii) the effects of boundary and testing conditions in the experimental evaluation of suffusion, and iii) summarize reference values of the hydraulic gradient triggering the initiation of suffusion. The thesis includes a literature review on the existing methods to evaluate soil’s susceptibility to suffusion, a comparison among the difference testing and boundary conditions applied in the experimental assessment of soil’s susceptibility to suffusion, and an experimental study aiming to determine the critical hydraulic gradient for suffusion to initiate in glacial till soils (ic). The experimental study includes three glacial till soils with particle size distributions representing different initial conditions in the core material, e.g.: internally stable, internally unstable and critically internally unstable. The boundary conditions considered in the test program are: initial void ratio, type of filter and specimen size. Test were performed with three different ratio of increase of hydraulic gradient and three different time interval to increase the hydraulic gradient. Results show that the Rönnqvist (2015) adaptation of the Kenney and Lau (1985, 1986) method modified by Li and Fannin (2008) is an accurate empirical method to evaluate the susceptibility of glacial till soils to suffusion. It was also concluded that the critical hydraulic gradient triggering suffusion is not a unique value but depends on the testing conditions, such as axial loading, rate of increase of hydraulic gradient (Δi) and time interval to increase hydraulic gradient (Δt). The higher the axial load the higher the critical hydraulic gradient needed to initiate suffusion. High ratio of increase of hydraulic gradient applied with short time interval can lead to ic - values higher than the obtained in tests with low Δi and long Δt. Tests should be performed with low rate of increase of hydraulic gradient and each hydraulic gradient should last long enough for the specimen to adapt/respond to the new hydraulic conditions. Nevertheless, a general observation is that the critical hydraulic gradient of internally unstable soils tends to be lower than 5 when tested without axial load.
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