Dynamic Characteristics of Jointed Rocks Subjected to Cyclic Loading
- Publication Type:
- Thesis
- Issue Date:
- 2023
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With the rising population and demand for mobility, the expansion of the transport system has become a major necessity in many countries, including Australia. Besides, the highly populated Australian coastal belt comprises jointed rocky terrains, and to extend rail transport infrastructure across these jointed rock formations, evaluating their dynamic mechanical behaviour, especially during the design stage of projects, is vital. Nevertheless, comprehensive research studies investigating the dynamic mechanical response of jointed rock formations subjected to cyclic loads that correspond to train loading conditions are extremely scarce. This study aims to investigate the dynamic mechanical behaviour and characteristics of jointed rocks under different cyclic loading conditions, including cyclic deviatoric stress amplitude, confining pressure, number of loading cycles corresponding to train loading conditions and joint surface roughness. Moreover, empirical relationships are proposed to predict crucial dynamic mechanical properties of jointed rocks.
Firstly, a cyclic triaxial test series was performed on planar, sawtooth and natural replicated rock joints at different confining pressures and cyclic deviatoric stress amplitudes. The test results demonstrated that with increasing cyclic stress and decreasing confining pressure, the maximum residual axial strain, dissipated energy, and damping ratio increased, with smoother joints exhibiting significantly higher values than rougher joints. Meanwhile, higher confining pressure and lower cyclic deviatoric stress corresponded to higher resilient moduli. Empirical relationships to predict the steady-state resilient moduli and damping ratio were developed.
Secondly, natural replicated rock joints were subjected to incremental cyclic deviatoric stresses under different confining pressures, and the test results demonstrated that there existed a critical dynamic deviatoric stress beyond which the yielding occurred, and this threshold increased with confining pressure. When the cyclic deviatoric stress exceeded the critical stress threshold, the accumulated residual axial strain, asperity damage, initial dissipated energy and damping ratio values were substantially higher. An empirical relationship was proposed for residual axial strain evolution under cyclic stresses surpassing the critical stress threshold. Furthermore, specimens were subjected to 500,000 loading cycles, and the test results illustrated that the resilient moduli exhibited a downward trend with cumulative residual axial strain. But resilient moduli were higher than Young’s moduli under the same confining pressure. Initially, the damping ratio rapidly decreased and increased slowly with cumulative residual axial strain. There existed a critical dynamic residual axial strain at which the damping ratio was the lowest. Empirical relationships were developed for the resilient moduli degradation and critical dynamic residual axial strain.
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