Sample preparation effects on the compaction properties of Swedish fine-grained tills

Sample preparation effects on the compaction properties of Swedish fine-grained tills Per Lindh & M.G. Winter Head of Malmö Branch, Swedish Geotechnical Institute, Hospitalsgatan 16 A, SE-211 33 Malmö, Sweden and Ph.D. Student at Dept. of Soil Mechanics, Lund University. Regional Manager (Scotland), TRL Limited, Redwood House, 66 Spylaw Road, Edinburgh EH10 5BR, UK F ine-grained tills are a dominant feature of the drift geology of Sweden. Until recently their use in earthworks applications has been limited due to the plentiful supply of naturally occurring gravel and crushed rock, and their high sensitivity to moisture content change which often leads to the view that fine-grained tills are problem soils. Environmental and economic factors are, however, leading to pressure to increase the use of site-won materials, including finegrained tills, in earthworks applications. This paper sets out the case for the increased use of fine-grained tills in such applications and examines the Moisture Condition Value test, for the determination of potential soil acceptability for earthworks, in the context of standards developed over 20 years in Britain and the emerging practice in Sweden. One of the key differences between Swedish practice and the approach followed in the British Standard is in terms of the sample preparation method employed. In Britain samples are air-dried prior to wetting to a range of moisture contents and testing while in Sweden an initially wet sample is selectively air-dried to achieve the desired range of moisture contents. The results of a detailed laboratory testing programme to investigate the influence of these sample preparation methods on the test results are presented. It is concluded that the Swedish method of selective air-drying is suitable for use in areas of high precipitation and associated high natural moisture contents. However, in areas where natural moisture contents are not consistently high the British Standard method is preferred. It is important to recognize that the sample preparation method employed will influence the test results and that the methods are not interchangeable. It is further found that, for the limited range of soils tested, there is no appreciable difference between the air-drying employed in the British Standard and oven-drying. However, it is recognized that further research is required in this area, not least on British soils.