Evaluation of dynamic properties of geomaterials using resonant column and cyclic torsional shear tests

Abstract

Geomaterials, such as soil and rock, form the foundation of many structures. Understanding how they respond to dynamic forces is essential for designing safe and resilient buildings, roads, and other infrastructure. This research is particularly relevant for regions prone to seismic activity and areas with significant human-made vibrations. In this thesis, the dynamic properties of geomaterials, specifically soils, and rocks, under varying dynamic loading conditions using Resonant Column and Torsional Shear (RCTS) equipment, have been investigated. The study encompasses the dynamic properties of sands and rocks, examining the impact of variables such as strain amplitudes, confining pressures, and loading frequencies. A critical aspect of the study is the evaluation of natural rubber latex (NRL) as a damping material in rock joints, which offers potential benefits in enhancing stability and energy dissipation in geotechnical applications. The deformational behaviour of sands indicates that increased strain amplitude decreases shear modulus while increasing damping ratio and higher confining pressures result in a higher shear modulus and lower damping ratio. The study also shows that higher relative densities lead to an increased shear modulus and decreased damping ratio. In dynamic response tests of intact rock, higher strain levels reduce shear modulus and increase the damping ratio. Loading rates also play a significant role, with higher rates reducing shear strain but increasing shear modulus and decreasing damping ratio. The investigation of jointed rocks reveals that the number of joints significantly affects their dynamic properties. More joints lead to a lower shear modulus and higher damping ratio. Additionally, the study demonstrates that increasing the loading frequency and confining pressure generally results in a higher shear modulus and lower damping ratio. Surface roughness and joint orientation also influence these properties, with higher roughness and joint orientation increasing shear modulus and decreasing damping ratio. The study employs advanced methodologies such as photogrammetry for estimating joint roughness coefficients (JRC), which proves to be a cost-effective and accurate alternative to traditional methods. Regression analyses using models like the modified hyperbolic model and Ramberg-Osgood model are utilized to fit experimental data and predict dynamic responses under various conditions. The comprehensive experimental and analytical approach provides valuable insights into the dynamic behaviour of geomaterials, which is essential for designing and assessing the safety and stability of geotechnical structures subjected to dynamic loads. The findings emphasize the significance of material-specific properties and testing conditions in predicting and enhancing the performance of geomaterials in engineering applications. The research concludes that NRL-grouted joints exhibit superior energy dissipation and stability, making them beneficial for various geological settings. Future research directions include optimizing the use of NRL in different contexts and further refining predictive models for dynamic behaviour based on the gathered experimental data. This study contributes to the broader understanding of the dynamic properties of geomaterials, aiding in the development of more reliable and resilient geotechnical engineering solutions.