| 1. |
- Al-Naqshabandy, Mohammed Salim
(författare)
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Strength variability in lime-cement columns and its effect on the reliability of embankments
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ground improvement by deep mixing (DM) is a generic term used for a number of methods in which a binding agent, often lime and/or cement, is mechanically mixed with the soil to increase its engineering properties. The inherent variability with respect to the engineering properties of the improved soil is high due to the variations in geology and the complex mixing process. High variability introduces uncertainty in estimating improved soil properties and the performance of the structure.Current design methodology deals with soil properties deterministically and the uncertainties involved are incorporated in a single value represented by a total factor of safety (FS). The chosen FS is highly dependent on the engineer’s judgment and past experience, in which both of these factors vary between different geotechnical designers. Therefore, current design methodology used in practice for DM does not deal with uncertainties in a rational way. In order to design a geotechnical system with the desired level of confidence, the uncertainties involved must be integrated in the DM design. This can be achieved by using reliability-based design (RBD) methods.The research work in this thesis is presented as a collection of three papers. In the first paper, a comprehensive statistical analysis of cone penetration test (CPT) data is described. The objective was to make a contribution to empirical knowledge by evaluating the strength variability of lime-cement columns within the group of tested columns. In the second paper, the effect of the spatial variability and statistical uncertainty with regard to the embankment’s reliability was investigated within the framework of RBD. The study in the third paper investigated the strength variability in lime-cement columns based on two test methods, namely CPT and column penetration test (KPS). In this study, the effect of different test methods on the evaluation of the design value was addressed.The main conclusions from this study can be summarized as follows. First, the probability distribution function (PDF) for the undrained shear strength of lime-cement columns can be modeled in RBD as normal or log-normal distributions. However, the use of log-normal distribution is recommended for RBD analyses. Second, the evaluated scales of fluctuation indicate ranges of 2 to 4 m and 0.2 to 0.8 m in the horizontal and the vertical directions respectively. This means that in order to fulfill the requirements of independent/uncorrelated samples for assessment of the design value, the spacing between samples must exceed the horizontal scale of fluctuation. It is therefore proposed that the spacing between individual samples should be at least 4 meters. Third, the design values evaluated using CPT and KPS were approximately the same. However, the inherent variability evaluated differs due to the larger volume tested with the KPS probe than with the CPT probe. However, this difference was not significant between the two tests. Fourthly, due to the limitation in the deterministic design in terms of dealing with uncertainties, it is recommended that RBD design should be used in parallel with the deterministic design of lime-cement column.
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| 2. |
- Bagheri, Mehdi
(författare)
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Model uncertainty of design tools to analyze block stability
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Block failure is one of the most common failure modes in tunnels. Design tools have some simplifications and, therefore, they also have some model uncertainties. The purpose of this licentiate thesis is to assess the model uncertainty for different design tools in order to estimate block stability. Different approaches of kinematic limit equilibrium (KLE) including conventional KLE, limited joint length, limited joint length and stress field consideration and probabilistic KLE were compared to that of DFN-DEM. In this approach, the results of the calibrated DFN-DEM with field mapping were considered to be of true value. The results show that the conventional KLE is overdesign due to it’s over simplification. By considering fracture length and stress field, the volume of predicted unstable blocks is reduced. The probabilistic approach of KLE by considering finite joint length and stress field predicts the volume of unstable blocks to be lower than DFN-DEM approach. Therefore there is a great model uncertainty of our standard design tools for block stability analysis. The assumption made in this study is that the results from DEM were considered to have a true value; the results from analytical solution based on joint relaxation process were compared to those of DEM in a different condition of depth, K0, apical and friction angle, Kn and Ks value, and ratio of Kn/Ks. The comparison shows that for shallow depth with K0 less than 1, analytical solution leads to an overestimation of block stability. The analytical solution predicts that the block is stable, while the analyses from numerical solution show the block is unstable. The analyses show that by increasing K0, accuracy of analytical solution also increases. Moreover, for the cases with close value of friction angle to semi-apical angle, the use of analytical solution is not recommended. As the ratio of Kn/Ks increases, the accuracy of analytical solution decreases. Increasing the angle ratio (ratio between semi-apical angle to friction angle) is one source of increasing uncertainty in the model. The analytical solution is very uncertain in cases with a low value of K0, and a high value of stiffness ratio and angle ratio. On the other hand, the analytical solution is more certain in conditions with a high value of K0 and a low value of stiffness ratio and angle ratio. According to current information (K0, angle ratio, stiffness ratio), one can determine the value of model uncertainty by using the diagrams presented in Chapter 6 of the thesis. The analyses show that by having more information about the key parameters, the model uncertainty could be identified more precisely. However, having more information means spending more money, and this increase in cost must be compared to the cost of failure or delay in the project or overdesign.
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| 3. |
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| 4. |
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| 5. |
- Bjureland, William
(författare)
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On reliability-based design of rock tunnel support
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tunneling involves large uncertainties. Since 2009, design of rock tunnels in European countries should be performed in accordance with the Eurocodes. The main principle in the Eurocodes is that it must be shown in all design situations that no relevant limit state is exceeded. This can be achieved with a number of different methods, where the most common one is design by calculation. To account for uncertainties in design, the Eurocode states that design by calculation should primarily be performed using limit state design methods, i.e. the partial factor method or reliability-based methods. The basic principle of the former is that it shall be assured that a structure’s resisting capacity is larger than the load acting on the structure, with high enough probability. Even if this might seem straightforward, the practical application of limit state design to rock tunnel support has only been studied to a limited extent.The aim of this licentiate thesis is to provide a review of the practical applicability of using reliability-based methods and the partial factor method in design of rock tunnel support. The review and the following discussion are based on findings from the cases studied in the appended papers. The discussion focuses on the challenges of applying fixed partial factors, as suggested by Eurocode, in design of rock tunnel support and some of the practical difficulties the engineer is faced with when applying reliability-based methods to design rock tunnel support.The main conclusions are that the partial factor method (as defined in Eurocode) is not suitable to use in design of rock tunnel support, but that reliability-based methods have the potential to account for uncertainties present in design, especially when used within the framework of the observational method. However, gathering of data for statistical quantification of input variables along with clarification of the necessary reliability levels and definition of “failure” are needed.
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| 6. |
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| 7. |
- de Frias Lopez, Ricardo
(författare)
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Granular Materials for Transport Infrastructures : Mechanical performance of coarse–fine mixtures for unbound layers through DEM analysis
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Granular materials are widely used as unbound layers within the infrastructure system playing a significant role on performance and maintenance. However, fields like pavement and railway engineering still heavily rely on empirically-based models owing to the complex behaviour of these materials, which partly stems from their discrete nature. In this sense, the discrete element method (DEM) presents a numerical alternative to study the behaviour of discrete systems with explicit consideration of the processes at particulate level governing the macroscopic response. This thesis aims at providing micromechanical insight into the effect of different particle sizes on the load-bearing structure of granular materials and its influence on the resilient modulus and permanent deformation response, both of which are greatly influenced by the stress level. In order to accomplish this, binary mixtures of elastic spheres under axisymmetric stress are studied using DEM as the simplest expression for gap-graded materials, which in turn also can be seen as a simplification of more complex mixtures.First, the effect of the fines content on the force transmission at contact level was studied. Results were used to define a soil fabric classification system where the roles of the coarse and fine fractions were defined and quantified in terms of force transmission.A behavioural correspondence between numerical mixtures and granular materials was established, where the mixtures were able to reproduce some of the most significant features regarding the resilient modulus and permanent strain dependency on stress level for granular materials.A good correlation between soil fabric and performance was also found. Generally, higher resilient modulus and lower deformation values were observed for interactive fabrics, whereas the opposite held for instable fabrics.Mixtures of elastic spheres are far from granular materials, where numerous additional factors should be considered. Nevertheless, it is the author’s belief that this work provides insight into the soil fabric structure and its effect on the macroscopic response of granular materials.
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| 8. |
- Deckner, Fanny, 1984-
(författare)
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Ground vibrations due to pile and sheet pile driving : influencing factors, predictions and measurements
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ground vibrations due to pile driving are part of a complex process. Vibration is generated from the pile driver to the pile. As the pile interacts with the surrounding soil, vibrations are transferred at the pile-soil interface. The vibration propagates through the ground and interacts with structures, both above ground and underground. The vibration continues into the structure where it may disturb occupants and/or damage the structure.In this thesis the study of the vibration transfer process due to pile driving is limited to the vibration source and the wave propagation in the soil. Vibration transmission to adjacent buildings and structures is not studied. However, impact of vibrations on buildings is briefly discussed in the literature study.It is important to accurately predict the magnitude of ground vibrations that result from pile driving in urban areas, both over- and underestimated vibration levels lead to increased costs. A lot of research has been performed within this field of knowledge, but a reliable and acknowledged prediction model for vibrations induced by pile or sheet pile driving is still needed.The objective of the research project is to increase the knowledge and understanding in the field of ground vibrations due to impact and vibratory driving of piles and sheet piles. This research project also aims to develop a reliable prediction model that can be used by practising engineers to estimate vibration due to pile driving. This licentiate thesis presents the first part of the research project and aims to increase the knowledge and understanding of the subject and to form a basis for continued research work.The most important findings and conclusions from this study are:The main factors influencing vibrations due to pile and sheet pile driving are; (1) the vibrations transferred from the pile to the soil, (2) the geotechnical conditions at the site and (3) the distance from the source.The vibrations transmitted from the pile to the soil depend on the vibrations transferred to the pile from the hammer, the pile-soil interaction and the wave propagation and attenuation in the plastic/elasto-plastic zone closest to the pile.There is today no prediction model that fulfils the criteria of the “perfect” prediction model; reliable but yet easy to apply.Future research should study the transfer of vibrations at the pile-soil interface, including the generation of a plastic/elasto-plastic zone in the area closest to the pile and how that affects the transfer of vibrations from the pile to the soil.
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| 9. |
- Dinegdae, Yared Hailegiorgis
(författare)
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Reliability-based Design Procedure for Flexible Pavements
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Load induced top-down fatigue cracking has been recognized recently as a major distress phenomenon in asphalt pavements. This failure mode has been observed in many parts of the world, and in some regions, it was found to be more prevalent and a primary cause of pavements failure. The main factors which are identified as potential causes of top down fatigue cracking are primarily linked to age hardening, mixtures fracture resistance and unbound layers stiffness. Mechanistic Empirical analytical models, which are based on hot mix asphalt fracture mechanics (HMA-FM) and that could predict crack initiation time and propagation rate, have been developed and shown their capacity in delivering acceptable predictions. However, in these methods, the effect of age hardening and healing is not properly accounted and moreover, these models do not consider the effect of mixture morphology influence on long term pavement performance. Another drawback of these models is, as analysis tools they are not suitable to be used for pavement design purpose. The main objective of this study is to develop a reliability calibrated design framework in load resistance factor design (LRFD) format which could be implemented to design pavement sections against top down fatigue cracking.For this purpose, asphalt mixture morphology based sub-models were developed and incorporated to HMA-FM to characterize the effect of aging and degradation on fracture resistance and healing potential. These sub-models were developed empirically exploiting the observed relation that exist between mixture morphology and fracture resistance. The developed crack initiation prediction model was calibrated and validated using pavement sections that have high quality laboratory data and observed field performance history. As traffic volume was identified in having a dominant influence on predicted performance, two separate model calibration and validation studies were undertaken based on expected traffic volume. The predictions result for both model calibration and validation was found to be in an excellent agreement with the observed performance in the field.A LRFD based design framework was suggested that could be implemented to optimize pavement sections against top-down fatigue cracking. To achieve this objective, pavement sections with various design target reliabilities and functional requirements were analyzed and studied. A simplified but efficient limit state equation was generated using a central composite design (CCD) based response surface methodology, and FORM based reliability analysis was implemented to compute reliabilities and formulate associated partial safety factors. A design example using the new partial safety factors have clearly illustrated the potential of the new method, which could be used to supplement existing design procedures.
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| 10. |
- Draganovic, Almir
(författare)
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Separations- och filtreringsstabilitet hos cementbaserat injekteringsbruk
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bleeding of cement based grout Bleeding of cement based grout is a complex problem. How it occurs and which basic mechanism causes and influences bleeding have been questions for discussion. Therefore the aim of the thesis is to illustrate what really happens with grout during bleeding and which factors influence it. In this way relevant measuring methods can be developed as well as the knowledge regarding how to interpret measuring results to joints in rock. The bleeding tests show that there are two basic mechanisms which cause bleeding. They are sedimentation and consolidation. It also means that the bleeding process is influenced by sample height. It was found that bleeding of coarse cement (ANL) was mainly a result of sedimentation of the grout. Experiment with fine cement (INJ30; d95<30 µm) shows that the consolidation part of bleeding was larger. The study shows that the bleeding process for a low sample height (10 mm) occurs fast. Extrapolation of experiment results and theoretical analysis shows that bleeding in a joint happens very fast and takes place during grouting itself. It means that results measured by standard methods can not be applied straight off for joints in rock. Theoretically bleeding occurs relatively slowly in vertical or inclined joints due to increased height. Bleeding will be resisted by arching and hardening. Reasonably, very little bleeding will take place. Filtration of cement based grout How far grout penetrates into a joint is not just influenced by the rheology of the grout like viscosity and shear strength, but also by the tendency of the grout to get stuck which means to build a plug. Factors which influence the building of a plug are properties of the grout, geometry of the joints including rawness of the joints and proceeding of the grouting. Today there are many different ways to measure filtration of a grout or the building of a plug. The different methods give different results and thus the importance of the influence of different factors is interpreted differently. The experiments in this thesis are done in a 100 mm long, 50 mm wide aperture with 1 mm width. Thereafter the width of the aperture decreases to 0.02 – 0.3 mm over a 10 mm long distance. The results of the experiments in this thesis, measured by own method, show that the best penetration ability with respect to filtration has a grout based on relatively fine-graded cement (INJ30; d95<30 µm).The penetrability of the grout based on more graded cement decreases because of flocculation. In total tens measurements have been done. The measurements confirm others’ experiments which show that the concentration of fine-graded particles (< 4 µm) has a large influence on flocculation and with that the building of larger grains. It is important to remind that the mixing of grout has been done by a laboratory mixer, which is not a mixer of colloidal type. This issue has to be further tested. The research shows that filtration of grout is also influenced by grain size of cement and the water cement ratio. The filtration test carried out by own measuring method with varying pressure showed a better penetrability for a larger pressure. It influenced both arching and erosion of the accumulated particles.
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| 11. |
- Gothäll, Rikard
(författare)
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Rock mass response during high pressure grouting
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The sealing of hard jointed rock by grouting involves several complicated mechanical systems. The result is a complex coupled system of hydro- logical and mechanical precesses. In order to determine the higher order effects of the resulting system the fracture deformations must be assessed. This requires a model that mimics the mechanical behaviour of not only fractures under normal load but also the entire rock mass system. This model indicates that there are two dominant regimes involved; a permeation regime and a high pressure regime. The pressure limit that separates permeation grouting from high pressure grouting can then be found to be closely related to the in situ stress. In the high pressure regime the deformations may be large but very situation-dependent. The principal deformational eigenmodes of some boundary conditions are considered. The analysis indicates that the usage of high pressure grouting can be both benficial to the operation as well as increase the inflow of water to the excavation.
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| 12. |
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| 13. |
- Johansson, Fredrik
(författare)
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Stabilitly analysis of large structures founded on rock : an introductory study
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Previous investigations of Swedish and international dams have shown difficultiesto assess the safety against failure in rock foundations. The problem was alsogiven additional interest in connection to the recent construction of the newbridge at Traneberg in Stockholm. This project was created in order to increasethe knowledge in the subject of stability analysis of large structures founded onrock, and how they should be performed in order to describe the safety in areliable way. This thesis covers the first half of this project. The objectives of the thesis were todescribe the knowledge and current state of practice in the subject with a literaturestudy, and with a case study of the arch dam at Krokströmmen show the problemsfor stability analyses where foundation and structure interact. The objective wasalso to produce a foundation for future work. At Krokströmmen arch dam, previous three dimensional finite element analyseshave been performed (Johansson and Palmgren 1996). In these analyses, thestiffness of the foundation was not considered. Based on the results from theseanalyses, stability was analytically analyzed for each monolith by Stille et al.(2002). The results indicated low factors of safety for the central monoliths. As aconsequence, a reinforcement slab was constructed to increase stability. In order to show how varying stiffness and non-linear resistance of the foundationaffects stability, a quasi three dimensional finite element analyses were carriedout. In these analyses, five of the central monoliths were first analyzed separately.Thereafter, the reaction forces were adjusted to fit the results from the analyses byJohansson and Palmgren (1996). The monoliths were thereafter coupled togetherwith assumptions of equal deformations and constant total reaction forces for thefive monoliths. Through an iterative procedure, constant deformation and newredistributed reaction forces were obtained. These forces were used to discuss thestability for one of the monoliths in detail. This thesis shows that the problem is more complex than described in the Swedishdam safety guidelines, RIDAS (Svensk Energi 2002), and the Swedish bridgedesign code, BRO 2004 (Vägverket 2004). An accurate analysis of the stability ina rock foundation under large structures demands a more refined approach, whichconsiders the specific features associated with rock mechanical problems. Thecase study showed that the interaction between foundation and structure can beconsiderable; deformations and reaction forces acting on the foundation wereredistributed when the stiffness of the foundation was considered. Furthermore,the resistance is a function of deformation. These aspects are necessaryconsidering if stability should be determined with high confidence. An additional question which was identified and brought up for discussion wasthe possibility of time-dependent deformation in the foundation at Krokströmmendue to creep and cyclic loading, which in turn can affect the long term stability.
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| 14. |
- Krounis, Alexandra
(författare)
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Uncertainty in Sliding Stability Analyses of Existing Concrete Gravity Dams with Bonded Concrete-Rock Interfaces
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Safety assessment of existing dams becomes more and more important with their increasing age. In addition, new regulations, due to climate changes and changes in knowledge, demand a re-evaluation of the existing dams’ safety. One of the failure modes considered in safety assessments of concrete gravity dams is sliding at the dam-foundation contact. Sliding failure is assumed to occur when the applied load exceeds the shear strength of the interface. Thus, the shear strength of the concrete-rock interface will ultimately determine if sliding of the dam will occur or not and it is, therefore, of utmost importance to be able to quantify it.The shear strength of concrete-rock interfaces is in general defined based on the Mohr-Coulomb shear strength criterion, which is governed by the cohesion, friction angle and normal stress along the interface. This simplified model of the shear strength is subject to several uncertainties, due for example to the natural variability of the involved parameters, statistical errors etc. In addition, analyses are commonly performed using the averaged values of cohesion, friction angle, normal and shear stresses, based on the assumption of ductile failure. This may be incorrect for bonded or partly bonded interface since test results show that bonded concrete-rock cores exhibit brittle behaviour.The uncertainties related to bonded or partly bonded interfaces are taken into account in the Swedish guidelines, RIDAS, for by treating all concrete-rock interfaces as unbonded, i.e. the effect of cohesion is not included when evaluating the shear strength of the interface. This is a conservative method, but it may lead to expensive and unnecessary strengthening of existing dams. Other deterministic guidelines/regulations, e.g. FERC, allow the use of cohesion but apply higher target safety factors when both the cohesive and the frictional strength are taken into account. To evaluate the adequacy of using cohesion in sliding stability analyses of concrete dams, the effect of the uncertainties on the calculated sliding stability of the dam has to be assessed.This thesis highlights several uncertainties related to bonded concrete-rock interfaces. However, the thesis focuses mainly on increasing the knowledge regarding the model uncertainty due to the brittle failure mechanism in combination with a possible spatial variability of cohesion. The magnitude of the model uncertainty is studied using numerical analyses. Its influence on the assessed behaviour of a hypothetical dam monolith is then evaluated using probability based methods. A conclusion drawn from this particular case, but which is likely to be generalized to other dam-foundation systems, is that the ductile sliding failure is too coarse an approximation of the failure behaviour of dams with bonded interfaces and could lead to an overestimation of dam safety. In addition, the potential spatial variability of cohesion along the interface further diminishes the validity of the ductile failure model.Areas that require further research in order to take into account the most significant uncertainties related to bonded interfaces include the definition of the ratio of bonded area to total area and its influence on sliding stability. The statistical uncertainty due to the limited number of tests also needs to be studied.
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| 15. |
- Lagerlund, Johan, 1979-
(författare)
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Remedial Injection Grouting of Embankment Dams with Non-Hardening Grouts
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis is to study the possibility of injection grouting of embankment dams affected by internal erosion. Internal erosion is a process where certain soil material from an embankment dam is removed. This phenomenon occurs in the central core of the embankment dam. If the internal erosion is allowed to continue over a longer period of time, the dam might face a fatal situation. Since the dam core is washed out, larger voids are created, thus lowering the geotechnical stability of the dam. If the voids become larger, more seepage is allowed to pass and if more seepage passes, the internal erosion process is accelerated. The central core in an embankment dam is preferably constructed with till. Till is a natural soil that origins from the ice age. The till contains a wide range of grain sizes, basically anything from clay to blocs. The mixture of grain sizes does however give the till characteristics that are highly desirable for a water retaining construction. It is cohesive, has a low permeability, a high angle of internal friction and can be found practically anywhere in Sweden. In an embankment dam the core is the water barrier. The core alone is however weak and cannot withstand the large external forces put on a dam construction. Because of this, several zones are constructed on both sides of the core. The first zone outside the core is the filter. The filter has no cohesion and is constructed with a coarser material than the core. Outside the filter, the shell is found. The shell is constructed with even coarser material than the filter and supports the entire dam structure. Outside the shell the riprap is found. The riprap protects the dam from erosive forces such as wave erosion, ice loads and heavy rainfalls. The filters main task is to protect the core from being washed out. Since the till in the core has a wide range of grain sizes, a constant rate of seepage may start to move its finer particles (clay, silt). If the filter doesn’t catch these moving particles, a loss of material will occur. This is the basis for internal erosion. If the till has a smooth particle size distribution curve it is less prone to internal erosion. The smoothness of the curve ensures that the different grain sizes involved are evenly distributed. The finer particles are mechanically locked in place by coarser particles, which in turn are mechanically locked by even coarser grains. Finally, the soil structure is more able to withstand the erosive forces provided by the seepage. If the finer particles aren’t mechanically locked and eroded by the seepage, the filter must be designed to catch them. Therefore, internal erosion occurs only if both the till and the filter flaws. If the internal erosion is continuous, the loss of material must be replaced. By doing so without dismantling the dam, injection grouting can be performed. The grout will replace the lost core material and restore the dam. The type of grout can basically be divided into two sub groups: 1. Hardening grouts; 2. Flexible grouts.
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| 16. |
- Lindgren, Mattias
(författare)
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Excavation in moraine and dense non-cohesive soil : Numerical analysis of soil behavior
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Excavation and moving of soil are common civil work tasks connected to the construction of buildings, roads and railways. In construction projects large amounts of soil have to be handled with different machines, tools and working methods. Soils are more or less difficult to excavate depending on their properties. The ability to excavate the soil (the excavatability) in combination with the type of work performed affects the choice of machines and tools being used. It also affects the time it takes to perform the work. The handling of soil volumes is a large part of the project cost. The cost depends on the machines and tools being used, the amount of soil being excavated and the ability to excavate the soil.The main objectives of this study are:• to identify parameters affecting the excavatability of soil through a literature review.• to study and describe the excavation process in soil.• to evaluate parameters affecting the horizontal resistive force on a wide blade with the finite element method.• to compare and discuss the magnitude of the horizontal resistive force obtained in the finite element study with calculations using an analytical model.• to propose a platform for further research in this area.The excavation process and the analysis of a tool working through the soil have been studied for three types of machine-tool sets. Earlier studies from different authors have provided important parameters that affect the resistance of soil as well as form a basis for the analysis of excavation and moving soil. A two-dimensional finite element analysis of a wide blade moving horizontally in a soil mass has been performed. The purpose of the numerical analysis was to analyse and discuss the effects of different soil and soil-tool parameters on the resultant resistive force acting on the blade.Based on the literature review, it was found that the particle size, the content of cobbles and boulders, the shear strength and the denseness of the soil affects the excavatability of the soil. When defining a model for predicting resistive forces on an excavation tool, it is necessary to study the total excavation process, including how the tool interferes with the ground, how the machine and tool moves and the methodology used for excavating and moving the soil.Based on the numerical analysis, it was found that, for undrained cohesive soil, the resistive force increases linearly with undrained shear strength and adhesion. For non-cohesive soil the resistive force increases non-linearly with the soil friction angle and the soil-tool friction angle, and linearly with dilatancy. Extended interfaces as well as different mesh sizes significantly impacted the magnitude of the resistive force.In order to determine the excavatability of soil and to present a new system for classification of excavatability, related knowledge is needed about the excavation process and the effect of the cobble and boulder content on the excavatability. Theoretical results obtained in this study must be verified by field tests.
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| 17. |
- Lucian, Charles
(författare)
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Geotechnical Aspects of Buildings on Expansive Soils in Kibaha, Tanzania : Preliminary Study
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this study is on potential problems resulting from construction on expansive soils in Kibaha region, Tanzania. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the soil behaviour and their interaction with structures, specifically as they relate to shallow foundations, has been of more interest to the study in order to evaluate properly the source of the problem. The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area. The geotechnical results are linked with the performance of the foundation as well as structures. Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples. The collected samples were submitted to soil laboratories at KTH and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests (free swell and swelling pressure). The results of this investigation indicate that soil in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell. Since swell potential and swell pressure are key properties of expansive soils, the swell parameters were measured by free swell tests and one-dimensional oedometer swell tests respectively. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa. The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of montmorillonite in the soil. It is from this fact that the source of the problem is in the expansive soils coupled with poor building materials. Physical conditions of the surveyed properties in the area confirmed the hypothesis of building damages due to poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations is supplemented with prototypes of strip foundations whose performances are to be monitored over a long period. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil.
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| 18. |
- Müller, Rasmus
(författare)
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Embankments founded on sulphide clay : - some aspects related to ground improvement by vertical drains
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, some aspects concerning building embankments founded on sulphide clay are studied, with special reference to ground improvement by preloading in combination with prefabricated vertical drains (PVD’s). The main purpose of the research was to increase empirical knowledge of the mechanical behaviour of sulphide clays subjected to embankment loadings and of the interaction between vertical drains and sulphide clays. Important aspects related to ground improvement with PVD’s in more general terms are also treated, in particular how various uncertainties regarding the properties of the clay and the clay-drain interaction imposed in the design phase can be addressed. The benefits of using theobservational method for handling these uncertainties are discussed, and a description of how the method was used in an embankment project is presented. The results from the research are presented in one conference paper and two papers submitted to peer-reviewed international journals, which are appended.The design of PVD’s involves describing the consolidation characteristics of the clay and the interaction between the drains and the clay. Primarily, the rate of consolidation is determined by the hydraulic conductivity (permeability) of the clay in the horizontal direction. Hence, accurate determination of this material property is of paramount importance in making reliable design predictions. As conventional laboratory tests for assessing the consolidation characteristics of a clay only provide information about its properties in the vertical direction, one is often left to make assumptions about the horizontal properties based on empirical correlations. Reliable empirical knowledge of these correlations for a certain clay is there forevital. A large number of CRS tests were performed on horizontal and vertical samples ofsulphide clay in order to investigate the correlation between the horizontal and verticalhydraulic conductivity and coefficient of consolidation. The results show that there is very small anisotropy in these parameters and that the scatters in the results are large. For designpurposes, sulphide clays should therefore be assumed to be isotropic in this respect. In orde rto handle the variation in properties, several parallel tests should be made and partial factors of safety should be introduced in the design. Introducing partial factors of safety in the design of PVD’s is one of the main topics suggested for further research. Regarding the clay-drain interaction, a study of the disturbance effects (smear effects) during the installation of drains in sulphide clays was performed. Back-calculations of measurements of pore pressure dissipation were made via a parameter study. It was shown that smear affects the consolidation rate to some extent but that the natural (undisturbed) hydraulic conductivity is more significant.The undrained shear strength su of a clay is dependent on the preconsolidation pressure σ 'p . As the clay consolidates under a loading, the effective stress increases, possibly to magnitudes surpassing the initial preconsolidation pressure and thereby leading to increased undrainedshear strength of the clay. The relation between su and σ 'p, i.e. the ratio su /σ 'p for asulphide clay, was investigated based on results from a large number of in situ tests andlaboratory tests. There were large scatters in the measurements, but su /σ 'p =0.25 is suggested as being relevant in the direct shear zone for design purposes in sulphide clays.
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| 19. |
- Nejad Ghafar, Ali, 1971-
(författare)
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An Experimental Study to Measure And Improve the Grout Penetrability
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An essential demand in any underground facility is to seal it against the water ingress to reduce the time and cost of the construction and the corresponding environmental hazards. To achieve this, obtaining sufficient grout spread is of great importance. Among the grouts, cement grouts with lower costs and environmental issues have been more reliable, whereas their main problem is filtration that restricts the grout spread. Several investigations have been therefore aimed to develop instruments to measure the grout penetrability as a fundamental means to improve the grout spread. Due to the difference in assumptions, limitations, and test conditions, and the deficiency in design their results are occasionally in contradiction. The question here is how to measure the grout penetrability more realistic? To answer this, two of the most frequently used instruments, Filter pump and Penetrability meter, were adjusted to approach the test conditions in Short slot. The results were discussed with respect to the origins of contradictions to better evaluate the reliability and functionality of the instruments.Among the influencing parameters on grout spread, applied pressure is a key element. The stepwise pressure increment is the method currently used to improve the grout spread in rock. Application of dynamic grouting has been studied as a solution to improve the grout spread for almost three decades. Despite some promising results, the method has not been yet industrialized due to the limited efficiency and issues in the type and frequency of the applied pressure, and the geometry of the test equipment. Therefore, finding a more efficient alternative of the applied pressure was the second goal of this study. A pneumatic pressure control system was consequently employed to examine the efficiency of the method in Short slot. The results conclusively revealed the effectiveness of the method and provided a strong basis for further development of the dynamic grouting.
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| 20. |
- Rahman, Mashuqur, 1984-
(författare)
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In-line rheology of cement grouts - Feasibility study of an ultrasound based non-invasive method
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Grouting is used in underground construction to reduce the water flow into tunnels and caverns and to limit the lowering of the surrounding groundwater table. Due to their wide availability and low cost relative to other materials, cement based materials are commonly used as grouts and, in this context, the rheology of the cement grout is an important factor. Rheological properties of cement grout such as viscosity and yield stress are commonly measured off-line using laboratory instruments, and some simple tools are available to make field measurements. However, these methods often lack accuracy and reliability. Although the rheological properties of the grout used play a fundamental role in design and execution, no method has yet been developed to measure these properties in-line in field work. In this work, for the first time, an in-line rheometry method combining the Ultrasound Velocity Profiling (UVP) technique with Pressure Difference (PD) measurements, known as “UVP+PD”, was successfully tested for continuous in-line measurements of concentrated micro cement based grouts. The feasibility of using the UVP+PD method depends on the in-line determination of the rheological properties and time dependent behaviour of the cement grouts. A test set-up consisting of a combination of an experimental “flow loop” and a conventional field grouting rig – UNIGROUT E22H – from AtlasCopco, was used to investigate the feasibility of determining the rheological properties of cement grout using the UVP+PD method under field conditions. A laboratory based test set-up was used to further investigate the rheological properties in a more controlled environment. The velocity profiles were measured directly in-line. The shape of the velocity profiles was visualized, and the change in the shape of the profiles with concentration and time was observed. The viscosity and yield stress of the grout were determined using rheological models, e.g. Bingham and Herschel-Bulkley. In addition, rheological properties were determined using the non-model approach (gradient method) and the tube viscometry concept and were compared with results obtained using the rheological models. In addition, the obtained rheological properties were subsequently compared with off-line measurements using a conventional rotational rheometer. The UVP+PD method was found to be capable of determining the true rheological behavior of cement grout regardless of the rheological model, providing the opportunity to visualize the change in the shape of the velocity profiles. Furthermore, it was possible to make an accurate determination of the velocity by ultrasound velocity profiling at a very flow rate (i.e. 1liter/min). The ultrasound velocity profiling was also found to be a reliable tool for determining the characteristics of the grout pump. In conclusion, the UVP+PD method was demonstrated to be a promising new in-line tool for determining the rheological properties of commonly used cement based grouts and the changes with concentration and time.
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| 21. |
- Spross, Johan, 1986-
(författare)
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A Critical Review of the Observational Method
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Building a sustainable structure in soil or rock that satisfies all predefined technical requirements implies choosing a rational and effective construction method. An important aspect is how the performance of the structure is verified. For cases when the geotechnical behaviour is hard to predict, the existing design code for geotechnical structures, Eurocode 7, suggests the so-called “observational method” to verify that the performance is acceptable. The basic principle of the method is to accept predefined changes in the design during construction, in order to accommodate the actual ground conditions, if the current design is found unsuitable. Even though this in theory should ensure an effective design solution, formal application of the observational method is rare. It is therefore not clear which prerequisites and circumstances that must be present for the observational method to be applicable and be the more suitable method.This licentiate thesis gives a critical review of the observational method, based on, and therefore limited by, the outcome of the performed case studies. The aim is to identify and highlight the crucial aspects that make the observational method difficult to apply, thereby providing a basis for research towards a more applicable definition of the method. The main topics of discussion are (1) the apparent contradiction between the preference for advanced probabilistic calculation methods to solve complex design problems and sound, qualitative engineering judgement, (2) the limitations of measurement data in assessing the safety of a structure, (3) the fact that currently, no safety margin is required for the completed structure when the observational method is applied, and (4) the rigidity of the current definition of the observational method and the implications of deviations from its principles.Based on the review, it is argued that the observational method can be improved by linking it to a probabilistic framework. To be applicable, the method should be supported by guidelines that explain and exemplify how to make the best use of it. The engineering judgement is however not lost; no matter how elaborate probabilistic methods are used, sound judgement is still needed to define the problem correctly. How to define such a probabilistic framework is an urgent topic for future research, because this also addresses the concerns regarding safety that is raised in the other topics of discussion.
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| 22. |
- Wersäll, Carl
(författare)
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Influence of Frequency on Compaction of Sand in Small-Scale Tests
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vibratory rollers are commonly used for compaction of embankments and landfills. In a majority of large construction projects, this activity constitutes a significant part of the project cost and causes considerable emissions. Thus, by improving the compaction efficiency, the construction industry would reduce costs and environmental impact. In recent years, rollers have been significantly improved in regard to engine efficiency, control systems, safety and driver comfort. However, very little progress has been made in compaction effectiveness. While the compaction procedure (e.g. layer thickness and number of passes) has been optimized over the years, the process in which the machine compacts the underlying soil is essentially identical to the situation in the 1970s.This research project investigates the influence of one crucial parameter, namely vibration frequency of the drum, which normally is a fixed roller parameter. Frequency is essential in all dynamic systems but its influence on the compaction efficiency has not been studied since the early days of soil compaction. Since laboratory and field equipment, measurement systems and analysis techniques at the time were not as developed as they are today, no explicit conclusion was drawn. Frequencyvariable oscillators, digital sensors and computer‐based analysis now provide possibilities to accurately study this concept in detail.In order to examine the influence of vibration frequency on the compaction of granular soil, small‐ scale tests were conducted under varying conditions. A vertically oscillating plate was placed on a sand bed contained in a test box. The experiments were carried out in laboratory conditions to maximize controllability. The first test setup utilized an electro‐dynamic oscillator where dynamic quantities, such as frequency and particle velocity amplitude, could be varied in real‐time. The second test setup included two counter‐rotating eccentric mass oscillators, where tests were conducted at discrete frequencies. This type of oscillator has a force amplitude that is governed by frequency.The main objectives of the tests were to determine the optimal compaction frequency and whether resonance can be utilized to improve compaction efficiency. Results showed that resonance had a major influence in the electro‐dynamic oscillator tests, where the applied force amplitude is low, and the optimal compaction frequency is the resonant frequency under these circumstances. In the rotating mass oscillator tests, where a high force was applied to the plate, resonant amplification was present but not as pronounced. Since force increase with frequency, the optimal frequency to obtain the highest degree of compaction is very large. In a practical regard, however, frequency should be kept as low as possible to minimize machine wear and emissions while still achieving a sufficient compaction of the soil. Considering the practical issues, it is proposed that surface compactors should operate slightly above the resonant frequency. However, the applicability to vibratory rollers must be confirmed in full‐scale tests.The thesis also presents an iterative method to calculate the frequency response of a vibrating plate, incorporating strain‐dependent soil properties. Calculated dynamic quantities are compared to measured values, confirming that the method accurately predicts the response.
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| 23. |
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| 24. |
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