Friktionsjords kornform: Inverkan på geotekniska egenskaper, beskrivande storheter och bestämningsmetoder
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
The fact that mechanical properties of a soil are depending on the shape of the soil particles, is something that is established in many studies and noted by many authors. It is stated that shear resistance of a coarse grained soil is higher in soils of angular and rough particles, than in soils made up by rounded and smooth particles. Furthermore it is known that the particle shape also influences on a number of other parameters. Although, the shape of soil particles is rarely taken into consideration when characterization of geotechnical materials is done. In design codes – such as Eurocode 7 and RIDAS 2008 – the guidelines about particle shape are not very clear. One of the few areas in which particle shape determination is applied, is the characterization of crushed aggregates, for use in e.g. the construction of roads and railways. As a result of the fact that there are a lot of difficulties and uncertainties in the area of particle shape determination and application in practice, the area has not been developed during the last decades. Lack of research has brought problems such as definitions that are not standardized, parameter relations that are not optimized, and a usage of terms and quantities that is very inconsistent. In most of reviewed literature in which it is dealt with analysis of a particle’s dimensions in different directions, the main application purpose seems to be determination of size or size distribution. In this context this thesis work – which aim has been to describe how particle shape affects a soil’s mechanical properties, and also identify and evaluate methods for defining and determining particle shape – is done. The shape of a particle is divided into the sub quantities sphericity, roundness and roughness. These parameters are describing the grain shape of large, intermediate and small scale. In the report it is reviewed how the particle shape effects on soil’s mechanical properties. Existing parameters describing particle shape, included the definitions, are analyzed. The report contains descriptions of three different methods for particle shape determination; by usage of the standard charts, by picture capturing followed by digital image processing (DIP), and by usage of methods based on laser technology. As a part of the work – done in order to obtain experience from an image analysis procedure’s all parts; sample preparation, imaging, result collection and analysis – some experimental work has been carried out. From these experiments results, consisting of pictures and values from the image analysis procedure, are obtained. In the report's analysis chapter there is one section focusing on the result values and the shape describing parameters. This part is followed by a second, in which the tested method – photographing and DIP-work – is analyzed. Finally there is a third section containing the analysis of other sub topics covered in the literature review chapter; e.g. usage of definitions, relations, terms, and also a little about in what way particle shape is affecting soil properties. It is in the report stated that there are many reasons to use the information that is given by determination of a material’s particle shape. This due to the fact that other parameters really are depending on the shape. Known particle shape is e.g. useful for prediction of the crushing effects of soil grains, tearing and other degradation processes, going on during long time. With the used method it is possible to, with results of good quality, by using the microscope camera, do 2D shape determination of grains with diameters 0,1252,0 mm. By using DIP, it is possible to objectively analyze many grains at the same time. The technique is quite simple and the needed equipment is mobile, but there are some significant drawbacks. The procedure of sample preparation may be time consuming, there is always a risk of errors originating from the analysis steps, and the result quality is always depending on to what extent the analyzed 2D-projections are representing the particles actual shapes. The shape parameter circularity is, due to its definition, to a greater extent than both AR2 and solidity, vulnerable to fluctuations and/or anomalies that cannot be attributed to an actual variation of the analyzed material particle shape. Caution is required when drawing conclusions regarding what general effects particle shape have on a soil’s deformation and strength properties. Shape determination techniques which are fast, accurate, repeatable and objective – e.g. photographing or laser scanning, followed by DIP-work – are preferable both when relations between parameters are developed, and when the same relations, later on, are used. Existing Swedish codes and guidelines, in which particle shape is mentioned, should be reviewed and clarified. This goes for advices, guideposts and laboratory methodologies. High and/or dynamic loads may, together with other types of breaking down processes, result in changed material properties and, furthermore, consequences as adverse settlements. Because of that, there may be reasons to review parts of existing design procedures related to usage of characteristic strength parameters, found in tables. This, to get the choice of material optimized for different load and deformation conditions. A cross-border work, between different areas of technologies in which known particle shape is of interest, would be bringing homogenization of term usage as well as developing of new and optimization of already formulated relations and definitions. This would be favorable for both the development of particle shape determination methods and for usage of the results.
Place, publisher, year, edition, pages
2011. , 146 p.
Teknik, friktionsjord, kornform, sfäricitet, kantighet, rundhet, cirkularitet, flisighet, portal, friktionsvinkel, standarddiagram, bildanalys, laserdiffraktion, laserskanning
IdentifiersURN: urn:nbn:se:ltu:diva-46153Local ID: 3cb1f609-3531-49d0-9a1b-0f28a34cfa30OAI: oai:DiVA.org:ltu-46153DiVA: diva2:1019466
Subject / course
Student thesis, at least 30 credits
Civil Engineering, master's level
Validerat; 20110617 (anonymous)2016-10-042016-10-04Bibliographically approved