Lime modification of clay till - A case study

Abstract: This report deals with lime modification of clay till. Lime modification means that the compaction properties of the soil are improved by the addition of lime. The report consists of three main parts: 1) Description of the geotechnical properties of clay till and how lime modification affects the properties; 2) Description of the implementation of lime modification and the tests conducted at a construction site in the northeast part of Lund, Sweden; 3) Evaluation of the test results. Clay tills are complex soils in earthworks. To be able to pack a clay till, it is required that the soil is in a solid consistency condition. Clay till is rarely found in a solid consistency condition. An ion exchange occurs through the addition of lime where calcium ions replace the existing ions surrounding the clay particles. The ion exchange leads to a structural change, which lowers the plastic limit and makes the soil packable. The modification has been carried out by Skanska and the measurements have been carried out by geotechnical consultants. The lime used during the modification has been quicklime and the amount of lime was 0.5 % and 1.0 %. The test methods used during the work have been plate load tests (static and dynamic), isotope meter and MCV test. The most important parameter in lime modification is the moisture content. An optimum moisture content exists for clay till. Quicklime is suitable when the moisture content exceeds the optimum. The porosity increases and results in a low stiffness at low moisture contents. The compaction work becomes easier by adding water before the mixing of lime. The amount of lime affects the result. A lime content of 1.0 % results in a smaller spread of porosity compared to a lime content of 0.5 %. Lime modification is an effective method for improving clay till in earthworks.