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 test embankments on sulphide soils at the test field in Lampen outside the city of Kalix next to the new rail road Haparandabanan. The main purpose of the licentiate thesis work was to improve the knowledge of compression properties of sulphide soils, with focus on the creep properties. Another aim was to establish a test field with extensive instrumented test embankments where settlements and pore pressures can be measured during many decades. The work with the test embankments has included instrumentation and construction as well as measurements of deformations, pore water pressures and soil temperatures. Field investigations of the properties of the sulphide soil have been performed mainly by CPTsounding, field vane test and Swedish piston sampling. An extensive program of laboratory tests, mainly through oedometer tests, both incremental loading and constant rate of strain, permeability tests and undrained direct simple shear tests, was conducted for the determination of compression and strength properties. In this work a literature review was performed with the subject sulphide soils and focusing on compression properties. A first simple one-dimensional calculation of the total settlements of the test embankments was carried out regarding the magnitude and the time dependency. The instrumentation and the construction of the test embankments have been carefully planned and were carried out as planned. The different measuring equipment as settlement hoses, bellow hoses, settlement gauges and inclinometers, which are installed in the embankments and the underlying sulphide soil to measure deformations in the soil, overall has given the expected values and the behaviour can be explained by theories of soil mechanics. The pore pressure responses in the underlying sulphide soil are related to the applied load caused by the mass of the embankments and the effective stresses in the soil. The results of the pore pressure measurements are comparable with previous experiences of the behaviour of load testing on fine-grained soils. Many oedometer tests, incremental loading and constant rate of strain (CRS), have been performed to study the compression properties of the sulphide soil and to evaluate different parameters. It has been possible to identify and evaluate the preconsolidation pressure from all the CRS oedometer tests, which indicates a good quality of the soil samples, .i.e. a well performed piston sampling and following handling of the soil samples. In comparison between the two different oedometer tests, incremental loading and constant rate of strain, the first one gave a slightly higher value of evaluated preconsolidation pressure. From the incremental loading tests the creep parameters, , and , were evaluated and they indicate that the values of these parameters in the sulphide soil from Lampen are slightly higher than the previous experiences of sulphide soils have shown. This implies that it can be relatively large differences in creep properties between different sites with sulphide soils and that incremental loading tests should be performed in the cases when creep settlements are of interest The total calculated settlements of the two embankments in Lampen after 50 years are between 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 latest measurements, i.e. 420 days after the start of the construction of the embankments, that the largest measured settlements of the ground surface were between 0.34 and 0.38 m. In comparison with the calculated results, these values were slightly higher, since the calculations 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 compression properties including creep properties of the investigated types of sulphide soils, with applications to settlement calculations of embankments.