Evaluation of cone factors for CPT-evaluation in CONRAD of sulphide- bearing soil in Mälardalen

Abstract: The purpose of this master thesis is to investigate how to evaluate CPT-soundings in sulphide soilfrom Mälardalen in CONRAD. The objective is to conclude whether sulphide soil from Mälardalenshould be evaluated with existing methods or a new method should be developed. The only existingevaluation methods for sulphide soil are empirically derived for sulphide soil along the coast of Gulfof Bothnia known as Svartmocka. There are currently no guidelines for when to use this evaluationmethod. In the industry, sulphide soil in Mälardalen is evaluated as clay for lack of alternatives, butthis solution has no scientific basis. There is therefore a need for an extended investigation on howsulphide soil from Mälardalen should be evaluated. Previous research has been summarized and provides the basis for the design of the analysis method. Geotechnical investigation data from two sites have been collected and analysed: Spångadalen, innorthwest Stockholm and part of the new railway Norrbotniabanan located north of Umeå in thenorthern part of Sweden. At Spångadalen, the main reason for the investigation is the construction oftwo storm water management ponds. Here some extended laboratory experiments have been carriedout to supplement existing data.Since the purpose of this thesis is to investigate how to evaluate the sulphide soil in Mälardalen, thedata from Spångadalen has be evaluated both with the method for clay and sulphide soil. The datafrom Norrbotniabanan has only been evaluated as sulphide soil. The comparison between theevaluation methods and areas is bases on the difference between the different investigation methods. The parameters of undrained shear strength, pre-consolidation pressure and overconsolidation ratiofrom CPT-soundings has been compared with the same parameters from direct shear tests, fall conetests, field vane tests and CRS. The comparison has also included the spread of the evaluated CPTs indifferent areas. Further the cone factors for the undrained shear strength and pre-consolidationpressure in the empirical equations in CONRAD has been evaluated for the soil in Spångadalen. Theevaluated in based on the evaluation of the CPT preformed in CONRAD and values for the undrainedshear strength and pre-consolidation pressure from other reference methods. The cone factors for theundrained shear strength and pre-consolidation pressure were then compared to the existing conefactors.The conclusion is that no significant results indicates that sulphide soil in Mälardalen differs fromclay although it shares some characteristic with the sulphide soil from Norrbotniabanan. Sulphidesoil from Spångadalen should not even be called sulphide soil since the amount of sulphide was toolow, which was discovered during the study. It should instead be called clay with elements of sulphide. Sulphide soil from Mälardalen should therefore continue to be evaluated as clay. However, furtherresearch on the subject is needed to ensure this conclusion for other areas with sulphide soil in Mälardalen.