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    Item type:Publication, Access status: without files ,
    Triaxial testing methodology for gassy soils
    (2023-09-15)
    Kaminski, Pauline
    ;
    Grabe, Jürgen
    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.
    Publicationtype: Journal Article
      21
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    Item type:Publication, Access status: without files ,
    A new simple shear apparatus and testing method for unsaturated sands
    (2015-01-01)
    Milatz, Marius
    ;
    Grabe, Jürgen
    This paper deals with a new simple shear apparatus for the investigation of mechanical soil behavior of unsaturated coarse-grained soils under monotonous and cyclic loading conditions. Non-cohesive soils, such as sands, typically encounter low capillary effects, and little research has been dedicated to them so far. This holds true especially for effects of repeated loading. The presented test setup allows control of small matric suction up to 85 kPa within the soil specimens with the help of a vacuum control method. Although the pore water pressures are negative as occurring in nature, the pore air pressure is kept at an atmospheric level. Depending on the pore water drainage condition of the specimen boundaries, either drained constant suction tests (CS-tests) or undrained constant water content tests (CW-tests) can be performed. The focus of the research is placed on the interaction of loading and volume change with matric suction and degree of saturation, i.e., the hydraulic-mechanical coupling, during monotonous and cyclic shear. Central questions are the impact of matric suction and degree of saturation on the densification behavior as well as, vice versa, the effect of cyclic loading on a change of matric suction and degree of saturation. The new simple shear apparatus and testing method will be explained, their benefits and shortcomings will be discussed, and selected results of a series of tests will be presented.
    Publicationtype: Journal Article
      70