Laboratory research on Swelling clay

This report is prepared to present the current interim status of the laboratory research on shrink and swell sensitive clays. The research is on-going, so this is to be read as an intermediate report. The report emphasizes the state of knowledge on the risks related to the phenomenon of potential shrink and swell in changing climatic conditions. The research is financed by Deltares by means of SITO funds with additional budget from NAM. The NAM budget has been used to take and test samples from Groningen, the SITO budget for the other locations and activities. In the coming years we will execute more and improved laboratory tests on samples from more locations so that we extend our knowledge about the relation between soil behaviour, soil properties and climatic circumstances, and by that supporting other activities we perform related to shrink and swell such as developing a risk map and a mathematical model. Since the dry period in 2018, problems related to the shrinkage and swelling of clay in The Netherlands became more profound. Deltares is conducting research on different aspects related to this phenomenon. For instance, aspects of this research are: • The construction of a risk map of the Netherlands, which displays areas where problems with shrink and swell of clays are to be expected. • The development of a mathematical model for predicting the behaviour of clay in-situ considering different scenarios. • Setting up monitoring sites to measure the behaviour of swelling sensitive clays in the field in response to varying climatic circumstances. • The measurement of swell and shrink of soils in the laboratory with respect to their composition, mineralogy and testing conditions. This report is the first interim report on the status and developments concerning the last item. The main objectives of this laboratory research are: • Relating soil composition and basic soil properties with the sensitivity for shrink and swell based on international published correlations. • Developing laboratory techniques and procedures especially for the research on shrink and swell of different clay types. • Measuring the shrink and swell of clays and determining shrink/swell parameters. • Developing a laboratory protocol related to shrink and swell. We have conducted the research on clay samples originating from different locations in the Netherlands; from the northern parts of Groningen to the western parts of Twente and in the river area central in the country. All investigated samples show shrink and swell tendencies. We have measured swell stress and strain which we used to determine the heave index (CH). This has led to promising results in the sense that reliable values have been determined which appear to be primarily related to the properties of the clay while being fairly independent of the specific testing conditions and initial state of the sample. Another index we have determined, the shrink swell index (ISS) didn’t yield promising results, since it appears to be overly dependent on only one specific test result, namely the shrink test. For both parameters more research is needed to be able to make a definitive decision about the validity of these parameters for Dutch clays. From the results of this research, it can be concluded that clays with swelling and shrinking properties are indeed present in The Netherlands. Swelling stresses which were too high for the standard equipment used were measured, resulting in a deformed porous stone. The measured stresses were higher than 1200 kPa, which is comparable to a 24-storey building.