Microscale investigation of bentonite distribution in pore spaces of sand after infiltration of stabilising solution

In the earth drilling method, which is an example of construction of structural foundations, the ground is excavated using a stabilising solution composed mainly of bentonite, and the trench walls are stabilised by an impermeable mud film formed on the trench walls. Microscopically, the mud film is supposed to be formed when bentonite in the stabilising solution occludes the pores, but this has never been experimentally verified. To elucidate the mechanism of mud film formation, a test apparatus of stabilising solution infiltration that can be applied to X-ray micro-computed tomography was developed, and the soil particle structure before and after infiltration of the stabilising solution is visualised. An image analysis algorithm was developed to investigate spatial and volumetric distribution of bentonite inside the sand. As a result, the formation of a uniformly continuous mud film was successfully visualised in three dimensions. Furthermore, it was found that bentonite occluded many pores in the sand, and that the higher the infiltration pressure, the larger the volume of bentonite that was spatially distributed. Under low infiltration pressure, small volumes of bentonite distribute over a wider area along the infiltration direction.