Shear Strength Parameters Of Clay Research Articles

Insight on bulk shear strength parameters of clay using discrete element approach incorporating physics-based interparticle force model

This paper aims to provide insight on factors affecting the bulk shear strength parameters of clay, i.e., the cohesion and internal friction as well as the effects of memory of preconsolidation pressure. A unique Discrete Element Method (DEM) model is built on platy particles with customized particle interaction force model. The particle interaction force model considers non-contact forces (such as the long-range electrostatic repulsion, short-range van der Waals attraction) as well as the direct contact force. The long-range electrostatic forces are calibrated by measurement with Atomic Force Microscope (AFM). Parameters for direct particle contacts of the regular DEM contact model, such as the contact stiffness and the friction coefficient, are calibrated by use of experimental consolidation and direct shear testing data. Computational simulations are conducted on digital clay specimen subjected to virtual direct shear tests. The predicted experimental responses of the digital specimens are consistent with typically observed in experiments including the shear stress-shear strain relationship, volumetric contraction and dilation, shear band formation, etc. From the stress–strain curves, the soil strength parameters are obtained with common experimental criteria. The DEM simulation results show that higher preconsolidation pressure drives more particles to overcome non-contact force into direct contacts and consequently bonding by van der Waals force. Consequently, the bulk cohesion of clay increases with increasing preconsolidation pressure. The results show that bulk cohesion strength is mainly attributed to the attractive interparticle force as well as the interlocking of platy particle, while the bulk internal friction angle is affected by the particle friction coefficient and particle fabric. Overall, the simulation results indicate the experimentally observed macroscopic shear strength parameters c and φ are linked to the microscope characteristics of soil particles and their mutual interactions. The results offer insight on the microscopic properties of particles on the bulk macroscopic strength behaviors. Besides, this work demonstrates a new strategy for simulation-based prediction of bulk soil strength parameters, by incorporating microscale characterization of the interparticle interactions and particle fabric into the particle-based DEM model.

Laboratory analyses of Kaolinite stabilized by vinyl polymers with different monomer types

The geotechnical behavior of a mixture of kaolinite and vinyl polymers with different monomer types was investigated using a series of laboratory tests. Three polymers were selected for chemical treating including synthesized poly(styrene-co-butyl acrylate) and poly(methyl methacrylate–co-butyl acrylate), and one commercial polyvinyl acetate. All these polymers were chosen to have a similar glass transition temperature (Tg). A series of laboratory tests were conducted on the prepared samples, including Atterberg limits, unconfined compressive strength, direct shear, swelling potential, oedometer, triaxial tests, and scanning electron microscopy observation. The results showed changes in the soil microstructures and considerable improvement in shear strength parameters of clay with all monomer types. Also, the highest strength was obtained in the stabilized samples with polyvinyl acetate among three stabilizers. Conversely, the swelling parameters of the polyvinyl acetate stabilized soil increased compared to the unstabilized soil. Finally, the stabilized samples with poly(methyl methacrylate-co-butyl acrylate) demonstrated better performance in reducing the swelling and increasing the strength properties of soil.

DISPERSIVE CLAY STABILISED BY ALUM AND LIME

Dispersion phenomenon can cause erosion problems during hydraulic construction projects such as earth dams, channels, hydraulic installations and embankments. However, aluminum sulfate can be used to stabilize dispersive clay. Tests were done to consider the effects of alum and lime additions on shear strength parameters of clay as secondary effects. Clay for samples was taken from the Mirzakhanluo Dam, located in Tarom County, northwestern Zanjan Province of Iran. In this research, the clay sample was subjected to direct shear testing; the clay was tested with optimum moisture under varying percentages of alum (0, 0.3, 0.6, 1, 3, and 5 as percentage of dry soil weight) for 28 days. Also, unconfined tests were conducted on samples with equal amounts of moisture, alum and lime under the different treatment durations of 7, 14, and 21 and 28 days, separately. Results for the direct shear test indicated that the maximum cohesion was recorded in the sample with 1% alum. Results also showed that the internal friction angle decreased in samples with alum percentage up to the level of 0.6% and at levels higher than that it showed an increase. Generally, results showed that soil shear strength was higher in soil stabilized by alum than in unstabilized soil. Results of the uniaxial test, determined that alum and lime additions to dispersive soil and its treatment, compression strength was not limited and elastic modulus showed an increase. The highest evaluations were determined for amounts of elastic modulus and uniaxial strength in soil with 3% lime or 5% alum on the 28th day of treatment.

Shear Strength Parameters and Consolidation of Clay Reinforced with Single and Group Bottom Ash Columns

Stone column could be used as a ground improvement technique where a portion of the soil is replaced with granular material such as crushed rocks or sand which is proven to increase bearing capacity and accelerate the dissipation of pore water pressure. Since “bottom ash”, as the waste of coal burning, possesses similar properties to sand, there is a potential of using bottom ash as stone columns. This paper discusses the results of the improvement in shear strength parameters of clay when reinforced with single and group bottom ash columns (BAC). A total of 39 specimens of kaolin samples were isotropically consolidated and sheared using Consolidated Undrained Triaxial Tests with pore pressure measurement to determine the shear strength parameters. Test variables include the diameter and height of columns and effective confining pressure. Results indicate that the installation of BAC in clay specimens increased the apparent cohesion but did not show any significant difference in the effective friction angle. Generally, the apparent cohesion of soft clay reinforced with partially penetrating columns is higher than that of fully penetrating columns. It is also found that during consolidation, the dissipation of pore water pressure was accelerated with the presence of BAC. Hence, it can be concluded that the consolidation and shear strength of soft clay could be improved by the installation of BAC.