Kompressionsegenskaper hos sulfidjordar : En fält- och laboratoriestudie av provbankar

Sammanfattning: In this licentiate thesis is presented the work and the results of the construction of two testembankments on sulphide soils at the test field in Lampen outside the city of Kalix next to thenew rail road Haparandabanan.The main purpose of the licentiate thesis work was to improve the knowledge of compressionproperties of sulphide soils, with focus on the creep properties. Another aim was to establish atest field with extensive instrumented test embankments where settlements and pore pressurescan be measured during many decades.The work with the test embankments has included instrumentation and construction as well asmeasurements of deformations, pore water pressures and soil temperatures. Fieldinvestigations of the properties of the sulphide soil have been performed mainly by CPTsounding,field vane test and Swedish piston sampling. An extensive program of laboratorytests, mainly through oedometer tests, both incremental loading and constant rate of strain,permeability tests and undrained direct simple shear tests, was conducted for thedetermination of compression and strength properties. In this work a literature review wasperformed with the subject sulphide soils and focusing on compression properties. A firstsimple one-dimensional calculation of the total settlements of the test embankments wascarried out regarding the magnitude and the time dependency.The instrumentation and the construction of the test embankments have been carefullyplanned and were carried out as planned. The different measuring equipment as settlementhoses, bellow hoses, settlement gauges and inclinometers, which are installed in theembankments and the underlying sulphide soil to measure deformations in the soil, overallhas given the expected values and the behaviour can be explained by theories of soilmechanics. The pore pressure responses in the underlying sulphide soil are related to theapplied load caused by the mass of the embankments and the effective stresses in the soil. Theresults of the pore pressure measurements are comparable with previous experiences of thebehaviour of load testing on fine-grained soils.Many oedometer tests, incremental loading and constant rate of strain (CRS), have beenperformed to study the compression properties of the sulphide soil and to evaluate differentparameters. It has been possible to identify and evaluate the preconsolidation pressure fromall the CRS oedometer tests, which indicates a good quality of the soil samples, .i.e. a wellperformed piston sampling and following handling of the soil samples. In comparisonbetween the two different oedometer tests, incremental loading and constant rate of strain, thefirst one gave a slightly higher value of evaluated preconsolidation pressure.From the incremental loading tests the creep parameters, , and , were evaluated andthey indicate that the values of these parameters in the sulphide soil from Lampen are slightlyhigher than the previous experiences of sulphide soils have shown. This implies that it can berelatively large differences in creep properties between different sites with sulphide soils andthat incremental loading tests should be performed in the cases when creep settlements are ofinterestThe total calculated settlements of the two embankments in Lampen after 50 years arebetween 1.12 and 1.35 m, with the heights 1.5 m and 2.0 m respectively of the embankments The performed measurements of the settlements showed at the time for the latestmeasurements, i.e. 420 days after the start of the construction of the embankments, that thelargest measured settlements of the ground surface were between 0.34 and 0.38 m. Incomparison with the calculated results, these values were slightly higher, since thecalculations for the same time give settlements in the order of 0.26 to 0.30 m.In this work an extensive experimental basis for the future has been created for compressionproperties including creep properties of the investigated types of sulphide soils, withapplications to settlement calculations of embankments.