Triaxial Testing Methodology for Gassy Soils

ABSTRACT
Small amounts of gas occur in almost every sediment inmarine or coastal environments. In past studies, a negative influence of gas on the mechanical properties of soil was associated with geohazard occurrence and dike safety in tide affected areas. However, the impact of a homogeneous distribution of gas bubbles in soil on its mechanical properties has not yet been thoroughly understood. In order to further investigate and improve our understanding of the shear strength of gassy soils, an experimental setup and a sample preparation procedure to implement the axis-translation method were developed. To this end, a temperature-controlled triaxial apparatus was specially modified. The triaxial apparatus is supplemented by a circulation system, required for the preparation of gassy samples with a homogeneous gas bubble distribution. In the circulation system, a defined quantity of carbon dioxide gas is dissolved in water. During the test procedure, the carbonated water is circulated into a saturated sample via a pressure gradient between the sample top and bottom. A subsequent unloading, tailored to the previously dissolved gas quantity, leads to gas exsolution in the sample. As a result, a defined degree of saturation can be generated within the triaxial apparatus. This experimental procedure represents a nondestructive technique for the preparation of gassy soil samples that is not limited to specific soil types. Triaxial shear tests on these samples extend our knowledge on the stress–strain behavior of gassy soils and thus provide a basis for future research, e.g., in
the field of constitutive modeling.

Keywords
triaxial testing, shear strength, gassy soil, gas exsolution, circulation, axis-translation method