A summary of initial self-sealing test results for selected argillaceous media in England

In recent years, there has been a resurgence in interest in the Thermal-Hydro-Mechanical-Chemical (THMC) properties of argillaceous rocks in England to assess their suitability for engineering projects such as water retention for reservoirs and containment of radionuclides for disposal of nuclear waste. A key factor in determining the suitability for these purposes is their ability to self-seal if fractured. The objective of our research is to measure the magnitude and rapidity of self-sealing predominately by swelling. At a macrostructural scale advective flow and capillary action draws water into fractures and pores. At a microstructural level fluid migrates into and out of clay-mineral-rich domains driven by mechanisms such as intra-crystalline swelling due to hydration of negatively charged clay mineral cations (to balance charge), and inter-crystalline osmatic swelling along ion concentration gradients (to balance ion concentrations) to rest around clay mineral and fine-grained particle surfaces. This double layer repulsion in the water shells pushes the clay minerals apart. This paper presents a summary of initial self-sealing test results carried out in a soil triaxial, at room temperature, under shallow stress and hydrogeological conditions. The tests were performed on samples of Oxford Clay Formation from two sites in Cambridgeshire.