Some laboratory studies of anisotropy of permeability of kaolin

[摘要] This thesis is concerned with an investigation into some aspects of the permeabilitymeasurement and permeability characteristics of reconstituted saturated supremekaolin clay. Development of permeability anisotropy is investigated when the samplehas experienced: (1) anisotropic consolidation, and (2) undrained shear.Conventional step-loaded consolidation tests, constant flow rate and some constanthead permeability tests were conducted on the kaolin slurry and block samples. Forevery conduct of testing, a pair of identical samples were tested: one underwentvertical drainage and the other radial drainage conditions. Both, however, weresubjected to one dimensional deformation in the vertical direction.Permeability of the clay was evaluated both directly and indirectly, from results ofthe permeability tests and consolidation tests, respectively. Data from the constantflow rate and constant head permeability tests yield the same values of permeabilityfor both cases of vertical or radial flow (kv not necessarily equal to Kh). Theoreticalconsiderations of the transient phase of the experimental record of the constant flowrate permeability test are found to be applicable to form the basis of evaluation ofpermeability, coefficient of consolidation, and coefficient of volume compressibility ofthe clay sample.Experimental results showed that during the progress of anisotropic consolidationof the kaolin slurry, the clay's vertical and horizontal permeability exhibited uniquerelationships 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 theoverconsolidation ratio. A lack of permeability anisotropy was observed in the earlypart of compression or at the initial void ratio, e = 3.1, but as the compressionproceeds, development of permeability anisotropy was observed to reach a value of upto 2.1 which correspond to a void ratio of 1.30, where the corresponding verticaleffective stress was 530kPa.Experimental results for the block samples that had experienced undrained shearalso showed the unique relationships of the clay's vertical and horizontal permeabilitywith void ratio. Development of permeability anisotropy, however, was somewhat inopposition with that of the slurry sample observed during anisotropic consolidation.For samples sheared to vertical strains of 7.9 to 11.5%, an initial permeabilityanisotropy of 1.3 at a void ratio of 1.66 was observed to decrease with compressionand developed into isotropic condition at a void ratio of 1.50, where the correspondingvertical effective stress was 120kPa. For samples sheared to vertical strains of 2.0 to5.0%, an initial permeability anisotropy of 2.5 at a void ratio of 1.30 was observed todecrease very little with compression and the degree of anisotropy remained to a valuexivof 2.3 at a void ratio 1.05, where the corresponding vertical effective stress was480kPa.Solutions from both the Terzaghi's and Biot's consolidation theories were used toevaluate the experimental data of the axisymmetric problem of consolidation withradial drainage to inner and outer fixed boundaries. Compared with measured values,permeabilities of the samples calculated from both the Terzaghi's and the Biot'ssolutions and using the Taylor'S square root of time method, are underestimated by afactor of 10 to 100 (ie. kcal/km = 1110 to 11100). Furthermore, the calculatedpermeabilities are less orderly in the l9.k vs e plot while the variation is more orderedand linear for the measured values.

[发布机构] University:University of Glasgow;Department:School of Engineering

[关键词] TA Engineering (General). Civil engineering (General)