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Sökning: hsv:(TEKNIK OCH TEKNOLOGIER) hsv:(Samhällsbyggnadsteknik) > Larsson Stefan

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1.
  • Andersson Schwarz, Jonas, et al. (författare)
  • A Platform Society
  • 2018
  • Ingår i: Developing Platform Economies : A European Policy Landscape - A European Policy Landscape. - 9789187379512 ; , s. 114-140
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • This chapter seeks to define the developing platform economy from a societal perspective, including the aspect of proprietorship, which forms a challenge both regarding transparency and accountability, but also fundamental aspects of datafication, scalability, automation, centralisation, and commercialisation.The societal effects of a few platform-based corporations (Google, Apple, Facebook, Amazon, Microsoft) are analysed, including the relationship to smaller, newer, platform-based companies that occasionally try to compete with them while often being dependent on them, or getting acquired. The importance of studying the type pf business model on which a platform’s growth or administration is based is here argued for, in order to be able to understand the logics of its growth, for example into multiple branches. Not only does an increasing number of social sectors and industries become dominated by digitally originated platform operators; also traditional institutional actors are increasingly adopting data-driven platform logics – utilising and analysing consumer data in order to predict particular outcomes in order to automate and outsource decision-making.
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2.
  • Al-Naqshabandy, Mohammed, et al. (författare)
  • Effect of Uncertainties of Improved Soil Shear Strength on the Reliability of Embankments
  • 2013
  • Ingår i: Journal of Geotechnical and Geoenvironmental Engineering. - 1090-0241 .- 1943-5606. ; 139:4, s. 619-632
  • Tidskriftsartikel (refereegranskat)abstract
    • The strength variability of soils improved by lime-cement columns is very high, and assessment of the reliability is associated with high uncertainty. Previous research on natural soils has shown that variability has a major impact on the reliability of geotechnical systems. However, concerning ground improvement with lime-cement columns, the effect of the uncertainties associated with improved strength properties on the reliability is unknown. This paper addresses the integration of reliability-based design in the design of embankments founded on soil improved by lime-cement columns by an analysis of a project conducted in Sweden. The uncertainties associated with estimating the strength property based on results from cone penetration tests and their effect on the assessed system reliability are addressed and discussed. The use of variance reduction with respect to the spatial variability of the shear strength of the columns was found to have a major influence on the assessed system reliability. Furthermore, it was found that the transformation uncertainty from measurements based on cone penetration tests has a significant impact on the assessed system reliability. System reliability cannot be improved significantly simply by performing a large number of tests.
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3.
  • Al-Naqshabandy, Mohammed Salim, et al. (författare)
  • Effect of spatial variability of the strength properties in lime-cement columns on embankment stability
  • 2012
  • Ingår i: Geotechnical Special Publication. - Reston, VA : American Society of Civil Engineers. - 0895-0563. ; 228, s. 231-242
  • Tidskriftsartikel (refereegranskat)abstract
    • Spatial variability with respect to the strength in lime-cement columns is an unavoidable source of uncertainty that should be considered in design. Current design method for the assessment of embankment stability, based on the deterministic factor of safety, cannot address the effect of spatial variability. Reliability-based design methodology is a powerful tool that can be used to integrate the variability into the analysis. In this paper, the spatial variability with respect to the undrained shear strength in the soil and in the columns was evaluated based on CPT test. The first order second moment (FOSM) reliability method was applied to address the impact of the spatial variability of the strength in the soil and in the columns on the reliability of an embankment founded on improved soil by lime-cement columns. The paper also presents a technique to evaluate the variance reduction factor over the failure surface. The results propose that the undrained shear strength in the soil and in the columns can be modelled following normal or lognormal distribution. The analysed example show that the reliability increased significantly when the spatial variability was considered
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4.
  • Al-Naqshabandy, Mohammed Salim (författare)
  • Strength variability in lime-cement columns and its effect on the reliability of embankments
  • 2011
  • 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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5.
  • Al-Naqshabandy, Mohammed Salim, et al. (författare)
  • Strength variability in lime-cement columns based on CPT data
  • 2012
  • Ingår i: Ground Improvement. - : Thomas Telford Ltd.. - 1365-781X .- 1751-7621. ; 165:1, s. 15--30
  • Tidskriftsartikel (refereegranskat)abstract
    • Natural and improved soils have relatively high inherent property variability that should be taken into consideration in design. Investigations of the spatial variability in lime-cement columns are important since they provide a rational quantification of the variability parameters needed for a reliability-based design analysis of geotechnical systems. Statistical analyses are used to evaluate the spatial variability parameters, i.e. the mean, the variance, and the scale of fluctuation, which is the distance within which soil properties reveal strong correlation. This paper presents a field test, in which 30 CPT soundings were performed and analyzed statistically in order to address the spatial variability in a group of lime-cement columns, with respect to the cone tip resistance. The objective of this paper is to describe the statistical analyses and to make a contribution to the empirical knowledge about strength variability in a volume of lime-cement columns. Stationarity has been assessed, and the scale of fluctuation has been evaluated in the vertical and horizontal directions. Random field theory was used based on the sample autocorrelation function ACF. The scale of fluctuation was found to be within the range of 0.2-0.7 m and 2-3 m in the vertical and horizontal direction, respectively. A simple design consideration shows that the variance reduction factor has a major influence on the determination of the design value.
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6.
  • Axelsson, Morgan, et al. (författare)
  • Column penetration tests for lime-cement columns in deep mixing - experiences in Sweden
  • 2003
  • Ingår i: Geotechnical Special Publication. - 0895-0563. ; 120, s. 681-694
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper column penetration tests for lime-cement columns in deep soil mixing are reviewed. In principle, column penetration tests and reversed column penetration tests are considered. Improved test techniques are presented and discussed based on tests from two test sites in Sweden. The investigations indicate that the reversed column penetration test is the most suitable method for the primary quality test with reference to the uniformity and continuity of the columns. The probe should, however, be installed by the lime-cement column machine short after the manufacturing of the column to avoid disturbances in the mixing process and to enable a random test selection.
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7.
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8.
  • Bergman, Niclas, et al. (författare)
  • Comparing column penetration and total–sounding data for lime–cement columns
  • 2014
  • Ingår i: Ground Improvement. - : Thomas Telford. - 1365-781X .- 1751-7621. ; 167:4, s. 249-259
  • Tidskriftsartikel (refereegranskat)abstract
    • In Sweden, the method commonly used for the quality control of lime–cement columns is the column penetration test. However, it is recommended for depths of no more than 8 m because the probe easily deviates from the column at greater depths. As an alternative to facilitate keeping the probe vertical, a centre hole is normally bored in the column using the total-sounding test method. The aim of this paper is to quantify the agreement between the two methods. If there is good agreement, it should be possible to use the less expensive and less time-consuming total-sounding test as a complement to the column penetration test. The analyses suggest good agreement between the methods, and it is therefore suggested that the total-sounding test be used as a complement to the column penetration test in evaluating the average strength properties of a group of medium- and high-strength lime–cement columns.
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9.
  • Bergman, Niclas, et al. (författare)
  • Variability of strength and deformation properties in lime-cement columns evaluated from CPT and KPS measurements
  • 2013
  • Ingår i: Georisk. - : Informa UK Limited. - 1749-9518 .- 1749-9526. ; 7:1, s. 21-36
  • Tidskriftsartikel (refereegranskat)abstract
    • The strength variability of soil improved by deep mixing with lime-cement columns is generally high. Eurocode 7 states that selection of characteristic values for geotechnical parameters shall take the variability of measured property values into account. This variability can be considered in the design by using reliability-based design. With reliability-based design, three statistical parameters are needed to evaluate the design value; mean, variance and scale of fluctuation. In this paper, the shear strength of soil improved by lime-cement columns was evaluated using two different penetration methods, the cone penetration test and the column penetration test. The strength was quantified statistically by the mean, variance and scale of fluctuation, while each test method was analyzed and discussed with a focus on its influence on the design value. Based on the analyses, the column penetration test is suggested as a test method for soil improved by lime-cement columns.
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10.
  • Draganovic, Almir, et al. (författare)
  • Ultrasonic dispersion of hard dispersed ultrafine milled cement-based grout for water sealing of fractured hard rock
  • 2022
  • Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 317
  • Tidskriftsartikel (refereegranskat)abstract
    • Ever higher demands on the sealing of rock around underground structures drive the development of cement based grouts. The results of the previous study demonstrated that it is possible to mill cement to approximately 20 to 25 mu m and use it to seal fracture aperture down to approximately 70 mu m. Further milling deteriorates the penetrability of the grouts due to the flocculation of the fine particles. This study investigates ultrasound as a technique to improve dispersion of grouts based on ultrafine milled cement. The grout tested is based on cement where 95% of the cement mass has particles smaller than 12 mu m and is very hard to disperse. Dispersion with ultrasound is compared with a conventional laboratory mixer equipped with a disk and rotor-stator system. The dispersion efficiency of this mixing equipment was tested by a filter pump. The results confirmed that a conventional laboratory mixer equipped with a disk is not at all suitable for dispersion of this grout. The laboratory mixer equipped with a rotor-stator system is much better than a disc but still cannot disperse this fine milled grout properly. Ultrasound was found to be the most effective method. The dispersion achieved, measured with a filter pump, was around 54 mu m which indicates that it is possible to seal fracture aperture now down to 54 mu m, which is a significant improvement.
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