| 1. |
- Bergliv, Elin, et al.
(författare)
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Laboratory study on two-dimensional image analysis as a tool to evaluate degradation of granular fill materials
- 2016
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Ingår i: Proceedings of Nordic Conference on Soil Mechanics and Geotechnical NGM. ; , s. 461-470
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Konferensbidrag (refereegranskat)abstract
- The shape of granular materials is known to affect strength and stiffness properties of soil and fills. Settlements in coarse fills are often explained by rearrangement within the soil skeleton induced by crushing and rounding of the individual aggregates in the intergranular contact points. These processes are not well investigated since it is difficult to measure changes at an aggregatelevel.Currently few attempts have been made to effectively measure and classify shape of granular soil and fill materials. One of the more promising methodologies is digital image analysis. Even if there are some studies on both two and three dimensional analyses on shape of aggregates, no study has focused on identifying shape changes as function of degradation effects of the fill materials.In this study degradation of ballast material has been studied in standardized micro Deval and Los Angeles tests and analysed by two dimensional image analysis and statistical methods. The results showed it was possible to statistically separate the shape and size of the materials before and after the degradation tests. To identify this difference it is essential to use more than one variable each for size and shape.The conclusion of the study is that two-dimensional image analysis can be used as a tool to measure and quantify shape changes on an aggregate level in order to measure degradation. If further developed, the technique can be useful to study deformation processes, e.g. crushing and rounding of aggregates, in coarse fill materials.
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| 2. |
- Bergliv, Elin
(författare)
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Large-scale testing of granular material
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main problem to investigate in this study is if larger grained materials, up to 200 mm nominal size, could be used as an embankment material for high-speed railways. High-speed railways have very strict settlement requirements, allowing only very small settlements to ensure safety.To be able to test large grained materials, large devices and unique equipment is needed, something that makes testing and laboratory investigations rarer with increasing grain size. The studies that have been done focus on materials up to about 200 mm nominal size. The literature review finds that there is unclear common conception of how grain size influences the shear strength and deformation properties of a soil material. The most common finding is that increasing grain size results in lower shear strength and increased deformations. Some studies found the opposite and some found no influence of grain size on shear strength. One observation is that the shear strength tends to be unaffected by grain size if the grain strength is equal for all grain sizes. Otherwise the general impression is that larger grains tend to have higher occurrence of fractures and cracks, lowering the grain strength.The study presented herein is performed with a newly developed large-scale simple direct shear device. This device allows testing of grains up to 200 mm grain size. The design includes a free-standing load frame, where the sample is placed in a steel-wire lined rubber membrane on a swing. There are two actuators, one applies vertical force on the sample, while the other applies the shearing motion of the swing. The design is new and allows large forces in both vertical and horizontal direction, without pre-stressing the device.A total of six series are performed on materials with varying grain size, gradation, and grain shape. The findings of the laboratory study includes higher shear strength of well-graded material with larger grains (0-200 mm) compared to a uniformly graded sand with grain size 0-2 mm. The main challenge with the laboratory testing was handling the large amounts of soil material needed for each sample, making it difficult to control the initial void ratio. This is a drawback when analysing the deformation behaviour of the tests. The general behaviour was that the samples underwent initially contraction, which ended with dilatancy and most test reached net increase of volume by the end ofthe shearing.
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| 3. |
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| 4. |
- Berglund, Andreas, et al.
(författare)
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Comparison between temperature based thaw weakening prediction model and field observation methods
- 2011
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Ingår i: Proceedings of the 21st International Conference on Port and Ocean Engineering under Arctic Conditions. - Montreal.
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Konferensbidrag (refereegranskat)abstract
- Structures like roads and port yards located in cold climate are affected by freezing and thawing every year. The global trend of a warmer climate and temperatures around 0°C for longer periods of time will change the freezing/thawing behaviour in many locations. The tendency will changeto have several freezing /thawing cycles in a given location every year. The bearing capacity of low volume roads and simple port yards will be affected by a prolonged thawing period with lower bearing capacity as a consequence. Bearing capacity problems can lead to increased costs for traffic as well as increased maintenance costs. Due to very high costs for destroyed structuresduring thaw, a lot can be gained if bearing capacity problems at a given site can be forecasted well in advance in order not to destroy the structure. Such a method should preferably be based upon simple measurements like air temperatures to make it easy to use also in remote areas. In the described temperature based model air and ground temperatures are used to develop anaccumulated thaw index and corresponding limits. When the thaw index limit is reached, the construction at the evaluated depth thaws, leading to increased pore water pressure and reduction of strength and bearing capacity. This paper presents a study of the application of the model at low volume roads in Sweden. Bearing capacity at the road was evaluated from field tests by falling weight deflectometer (FWD) test carried out 24 times during the thawing season i.e.March 4 through June 9. Predictions made by the model were compared with the subgrade module evaluated from the FWD series. The results show that the model might be possible to use in Sweden and elsewhere if minor adjustments are carried out.
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| 5. |
- Bhanbhro, Riaz, et al.
(författare)
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Basic description of tailings from Aitik focusing on mechanical behavior
- 2013
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Ingår i: International Journal of Emerging Technology and Advanced Engineering. - 2250-2459. ; 3:12, s. 65-69
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Tidskriftsartikel (refereegranskat)abstract
- Tailings are artificial granular materials that behave different as compared to natural soil of equal grain sizes. Tailings particle sizes, shapes, gradation and mechanical behavior may influence the performance of tailings dams. Hence it is essential to understand the tailings materials in depth. This article describes present studies being carried out on Aitik tailings. Basic tailings characteristics including specific gravity, phase relationships, particle sizes, particle shapes and direct shear behavior are presented in this article. The results showed that particles size decreases along depth from surface for collected sample locations. The angularity of the particles increases as the grain size decreases. Vertical height reduction was observed during shearing of samples by direct shear tests.
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| 6. |
- Bhanbhro, Riaz, 1985-, et al.
(författare)
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Effect of Particle Size On Mechanical Properties and Particle Breakage of Tailings
- 2017
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Ingår i: Canadian geotechnical journal (Print). - 0008-3674 .- 1208-6010.
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Tidskriftsartikel (refereegranskat)abstract
- Tailings material can have different material properties depending upon the type of ore and ore refining process and particle size distribution. Tailings dams are constructed as walk away solutions. Staged construction of tailings dams may lead to breakage of particles in subsequent layers resulting in change in particle sizes of material. This may lead to change in strength parameters upon change in particle sizes. This paper presents the direct shear tests performed on tailings material from a tailings dam. Remolded samples were manufactured in laboratory. The tailings material is separated in to four different particle sizes i.e.1-0.5mm, 0.5-0.25mm, 0.25-0.125mm and 0.125-0.063mm. The tests are performed on different normal stress levels as 50, 100, 150, 300 and 500kPa.The strength parameters are evaluated for each particle size and compared with said particle sizes. In order to study the effect of deposition, the tests are also performed on same material deposited in vertical and horizontal direction. This paper also describes the study of breakage of particles during direct shear tests by sieving the material at the end of each test.
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| 7. |
- Bhanbhro, Riaz, et al.
(författare)
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Evaluation Of Primary And Secondary Deformations and Particle Breakage of Tailings
- 2015
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Ingår i: From Fundamentals to Applications in Geotechnics. - : IOS Press. - 9781614996026 - 9781614996033 ; , s. 2481-2488
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Konferensbidrag (refereegranskat)abstract
- Tailings are the waste product of mining which is left over after extraction of materials of interest. Tailings material may possess different material properties depending upon type of ore and method of concentration. Sometimes the tailings material itself is used in construction of tailings dams and tailings dams are constructed to withstand for long times. A tailing dam can be exposed to settlements due to incremental load as these dams are raised in stages. Increasing load with time may also lead to particle breakage. This article presents the results from oedometer tests conducted on tailings materials. The study includes the stress-deformation behavior and particle breakage of tailings material of different gradations upon application of incremental loads in oedometer tests. The samples were collected from different sections of tailings dam from Sweden. Remolded samples were manufactured in laboratory as four batches of particle sizes i.e. 1-0.5 mm, 0.5-0.25mm, 0.25-0.125mm and 0.125-0.063mm. The results are analyzed from tested samples at different stress levels and compared with different particle sizes. The breakage of particles of each batch is analyzed by sieving the specimens after oedometer tests. The results are evaluated in terms of primary and secondary deformations. The primary and secondary deformations are also compared with different particle sized specimens.
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| 8. |
- Bhanbhro, Riaz, et al.
(författare)
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Mechanical Behavior of Uniformed Tailings Material in Triaxial Tests
- 2017
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Ingår i: Electronic Journal of Geotechnical Engineering. - : Mete Öner. - 1089-3032. ; 22:06, s. 1717-1730
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Tidskriftsartikel (refereegranskat)abstract
- Tailings dams are raised with time depending upon rate of generation of waste. A tailings dam can contain different particle sized materials within its dam body. The newly raised embankment in a tailings dam can be considered as vertical load being applied on subsequent layer. The applied loads can cause deformations and breakage of particles. The particle breakage can then lead to a skeleton with new particle size particles and hence can lead to new material properties. This paper provides the results from triaxial tests conducted on uniformed particle sizes as, 0.5mm-0.25mm, 0.25mm-0.125mm and 0.125mm-0.063mm. The tests are performed at various effective radial stresses. The results are evaluated and compared with each particle size. The results include stress-strain and volumetric behavior during shearing, the effective stress ratio and stress-dilatancy plot. The friction angles are also evaluated and compared with different particle sized specimens. It was found that effective stress ratios were slightly higher when tests were performed at lower confining stresses and vice versa. It was also observed that particle size did not show any effect of friction angles.
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| 9. |
- Bhanbhro, Riaz, et al.
(författare)
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Mechanical Properties and Particle Breakage of Uniform-Sized Tailings Material
- 2021
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Ingår i: Journal of materials in civil engineering. - Luleå : American Society of Civil Engineers (ASCE). - 0899-1561 .- 1943-5533. ; 33:3
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Tidskriftsartikel (refereegranskat)abstract
- Tailings dam disasters are reported almost every year and are triggered by mechanisms, such as overtopping, piping, and others.The failures due to inadequate management cannot be neglected as well. These dams are constructed mostly in a step-by-step constructionmethod that leads to a continuously changing state of vertical loads during construction and may lead to particle breakage and changes instrength. Therefore, a layer of tailings dam today may not be the same tomorrow during the construction phase. To study the effects ofdifferent loads on particle breakage and strength, direct shear tests were performed on remolded tailings samples that were separated intodifferent particle sizes. The tests were performed using different normal stresses that ranged from 50 to 500 kPa. The results indicate that finertailings exhibited slightly more shear resistance than that of coarser tailings irrespective of the deposition method. For normally depositedspecimen, the dilatant and contractant behavior in vertical height was observed when the normal effective stress was less than 300 kPa andgreater than 300 kPa, respectively. Under the vertical deposition method, the finer tailings showed contractant height behavior when subjectedto a normal effective stress of 300 kPa. The friction angle and the cohesion of vertically deposited specimens were slightly higher and slightlylower, respectively, than that of normally deposited ones. The breakage of tailings particles was observed to be proportional to the particle sizeof the tailings.
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| 10. |
- Bhanbhro, Riaz, et al.
(författare)
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Mechanical Properties of Soft Tailings from a Swedish Tailings Impoundment : Results from Direct Shear Tests
- 2014
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Ingår i: Electronic Journal of Geotechnical Engineering. - 1089-3032. ; 19:Z, s. 9023-9039
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Tidskriftsartikel (refereegranskat)abstract
- The shear strength of tailings can vary depending upon the type of ore and method of construction. Tailings dams may possess loose layers in subsequent layers, which may have low shear strength. Since the tailings dams are made-up to last for longer times, the strength parameters and material behaviors are essential to understand, especially potential for static liquefaction in loose layers. This article presents the results from direct shear tests performed on samples from loose layer of a tailings dam. Both drained and undrained tests are carried out. The results indicated the strain hardening behavior in tailings material which indicates loose condition. The shear strength was found to be relatively low as compared to typical values of tailings in literature. A contractant volume behavior was observed for all the tests. During shear tests the vertical height reductions in samples were observed. These changes were significantly increased after peak shear followed by slight increment in pore pressure along shearing angle. The reasons for these height changes are not fully known, but may be a rearrangement in skeleton or breakage of particles during shear which needs further investigative studies.
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