Some laboratory studies of anisotropy of permeability of kaolin
This thesis is concerned with an investigation into some aspects of the permeability measurement and permeability characteristics of reconstituted saturated supreme kaolin clay. Development of permeability anisotropy is investigated when the sample has experienced: (1) anisotropic consolidation, and (2) undrained shear. Conventional step-loaded consolidation tests, constant flow rate and some constant head permeability tests were conducted on the kaolin slurry and block samples. For every conduct of testing, a pair of identical samples were tested: one underwent vertical drainage and the other radial drainage conditions. Both, however, were subjected to one dimensional deformation in the vertical direction. Permeability of the clay was evaluated both directly and indirectly, from results of the permeability tests and consolidation tests, respectively. Data from the constant flow rate and constant head permeability tests yield the same values of permeability for both cases of vertical or radial flow (kv not necessarily equal to Kh). Theoretical considerations of the transient phase of the experimental record of the constant flow rate permeability test are found to be applicable to form the basis of evaluation of permeability, coefficient of consolidation, and coefficient of volume compressibility of the clay sample. Experimental results showed that during the progress of anisotropic consolidation of the kaolin slurry, the clay's vertical and horizontal permeability exhibited unique relationships with the void ratio which are linear on the logarithmic-linear scale [linear (lg k vs e) plot ]. These relationships were found to be independent of the overconsolidation ratio. A lack of permeability anisotropy was observed in the early part of compression or at the initial void ratio, e = 3.1, but as the compression proceeds, development of permeability anisotropy was observed to reach a value of up to 2.1 which correspond to a void ratio of 1.30, where the corresponding vertical effective stress was 530kPa. Experimental results for the block samples that had experienced undrained shear also showed the unique relationships of the clay's vertical and horizontal permeability with void ratio. Development of permeability anisotropy, however, was somewhat in opposition with that of the slurry sample observed during anisotropic consolidation. For samples sheared to vertical strains of 7.9 to 11.5%, an initial permeability anisotropy of 1.3 at a void ratio of 1.66 was observed to decrease with compression and developed into isotropic condition at a void ratio of 1.50, where the corresponding vertical effective stress was 120kPa. For samples sheared to vertical strains of 2.0 to 5.0%, an initial permeability anisotropy of 2.5 at a void ratio of 1.30 was observed to decrease very little with compression and the degree of anisotropy remained to a value xiv of 2.3 at a void ratio 1.05, where the corresponding vertical effective stress was 480kPa. Solutions from both the Terzaghi's and Biot's consolidation theories were used to evaluate the experimental data of the axisymmetric problem of consolidation with radial drainage to inner and outer fixed boundaries. Compared with measured values, permeabilities of the samples calculated from both the Terzaghi's and the Biot's solutions and using the Taylor'S square root of time method, are underestimated by a factor of 10 to 100 (ie. kcal/km = 1110 to 11100). Furthermore, the calculated permeabilities are less orderly in the l9.k vs e plot while the variation is more ordered and linear for the measured values.