Computer tomographic analysis of undisturbed samples of loose sands

Abstract

Spontaneous flows of very loose sand deposits pose a serious environmental problem in abandoned lignite mines. Large areas in eastern Germany are not safe for public access. Slight disturbances have triggered large settlement flows, causing loss of lives and structures. To better understand the mechanisms of fast settlement flows, undisturbed samples from depths between 10 and 15 m below ground level were retrieved using the soil-freezing method. Conventional laboratory and computer tomographic soil analyses were performed on these samples. The results reveal a very low degree of saturation and large gas-filled macropores responsible for considerable density fluctuations within the phreatic zone. These spatial porosity variations are thought to strongly contribute to the collapsibility of loose sands.Key words: spontaneous liquefaction, undisturbed sampling, soil freezing, computer tomography, density fluctuations, gas inclusions.