Regression-Based Analysis of Strain Softening in Triaxial Response of Indian Coal Ashes Using Hyperbolic Model

India is primarily dependent on thermal power plants for its energy needs. Large quantities of coal ashes emanate as a by-product of this process. Coal ashes produced in form of bottom ash and fly ash are often mixed with large quantities of water for wet disposal and sluiced to on-site ash ponds. Recently, considerable emphasis has been laid on suitable utilization of coal ashes in various infrastructure development projects. However, prior to any application their behavior, particularly, the shear strength characteristics under varied loading and drainage conditions needs to be carefully examined. In this study, a numerical model has been developed to analyze the post-peak strain softening behavior of coal ashes. A co-ordinate system transformation approach is employed based on the classical Duncan-Chang hyperbolic curve to model the softening behavior of undrained coal ashes. The validation of the model has been accomplished using triaxial data of six pond ash and four fly ash specimens randomly selected from various Indian power plants. Furthermore, a multi-variable regression analysis has also been carried out to develop empirical relationships between the model parameters and stress and strain values corresponding to peak and residual state, and confining pressure of the sample.