Compressibility and permeability of Bangkok clay compared with kaolinite and bentonite

摘要

The physical and engineering properties of remolded clays are intrinsic and can be used as a frame of reference for the behavior of clay. Compressibility and permeability of remolded Bangkok clay at different ion concentrations and valences were compared with kaolin and bentonite as representatives of non- and high swelling clays. Bangkok clay, a low-swelling clay, exhibited physical and engineering properties similar to those of kaolin. The texture of coagulated Bangkok clay became a more flocculated structure with increasing ion concentration and valence, resulting in higher water holding capacity and liquid limit. Even though the physical properties of all tested clays varied significantly with pore water chemistry, the (PI, LL) points lied above the A-line in the plasticity chart (where PI is the plasticity index and LL is the liquid limit) and could be represented by a unique relationship. The change of the intrinsic compressibility and permeability with the concentration and valence of the ions was interpreted by a generalized stress state e/e_L. The lower e/e_L value was associated with higher shear strength (resistance to vertical consolidation pressure in K_0-consolidation) and lower permeability. As the ion concentration and valence were increased for both kaolin and Bangkok clay, the resistance to consolidation pressure increased and permeability decreased for the same void ratio due to the decrease in e/e_L. The liquid limit for bentonite decreased with increasing ion concentration and valence due to the compression of the diffuse double layer. Hence, for the same void ratio, the resistance to consolidation pressure decreased and permeability increased due to the increase of e/e_L. Finally, relationships of the modified void index, I'_v and consolidation pressure, σ'v, and generalized stress state e/e_L and permeability k were proposed. These relationships are useful and practical tools for assessing the intrinsic compressibility and permeability of non- to high-swelling clays in terms of liquid limit, which is easily obtained from conventional laboratory tests.