Cyclic Loading Effects on Rock Mechanical Properties

Cyclic loading, characterised by repeated application and removal of stress, profoundly influences the strength, stiffness and damage evolution of rock. Under cyclic stress paths, rocks exhibit non-linear stress–strain behaviour, energy dissipation and progressive accumulation of irreversible deformation. Key processes include microcrack initiation and coalescence, pore collapse or compaction, and fatigue damage, all of which depend on loading amplitude, frequency, confining pressure and rock fabric. Acoustic emission monitoring and advanced imaging reveal that the first few cycles often induce the greatest inelastic strain and crack activity, after which damage rates may stabilise or accelerate towards failure. Constitutive models integrating elastic, viscoelastic, plastic and damage mechanics now capture hysteresis, modulus degradation and fatigue life, aiding the prediction of reservoir compaction, tunnel convergence, hydrocarbon well integrity and seismic response. Understanding cyclic loading effects is therefore essential for the safe design of underground energy storage, hydraulic fracturing, mining operations and civil infrastructure in seismically active regions.

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Recent studies combining laboratory tests and constitutive modelling have clarified sandstone response to cyclic loading relevant for underground energy storage. Experiments under varying mean stress, amplitude and frequency show that inelastic strain and acoustic emission counts peak in the initial cycle before settling to a lower steady rate. A hybrid model incorporating modified Cam-Clay and damage mechanics accurately reproduces observed hysteresis loops, elastic-plastic transitions and brittle creep, demonstrating the role of stress path in controlling compaction and dilatant cracking.

Investigations of shale under triaxial cyclic loading and unloading have used both physical tests and discrete-element simulations to map fatigue damage. By quantifying dissipated energy, plastic strain and modulus reduction, these works reveal that even a limited number of cycles can produce significant strength loss when confining pressure is low. Microcrack distribution patterns extracted from simulation agree with acoustic emission trends and highlight the influence of loading path on fracture orientation and energy dissipation.

True triaxial cyclic loading experiments on pre-cracked sandstone samples have elucidated the evolution of total, elastic, dissipated and plastic energy densities. These energies grow with cycle number and exhibit quadratic dependence on the upper stress limit. Varying crack orientation alters the balance between energy storage and dissipation, explaining differences in fatigue life and peak strength as a function of natural fracture angle.

Cyclic Loading Effects on Rock Mechanical Properties publication trend

The graph below shows the total number of articles in cyclic loading effects on rock mechanical properties across all publications each year (not limited to Nature Index journals).

Technical terms

Cyclic loading: Repeated application and removal of stress or strain to a rock sample, inducing progressive damage.

Acoustic emission: Transient elastic waves generated by sudden microcrack growth or frictional sliding within rock.

Confining pressure: External pressure applied uniformly around a rock sample to simulate in situ stress conditions.

Hysteresis loop: The closed curve on a stress–strain plot formed during a loading–unloading cycle, indicating energy loss.

Microcracking: Development and propagation of small fractures within the rock’s microstructure under load, leading to stiffness degradation.

References

1. Experimental and numerical investigation of sandstone deformation under cycling loading relevant for underground energy storage. Journal of Energy Storage (2023).
2. Experiment and DEM simulation study on mechanical behaviors of shale under triaxial cyclic loading and unloading conditions. Geomechanics and Geophysics for Geo-Energy and Geo-Resources (2023).
3. Energy characteristics of sandstones with different crack angles under true triaxial cyclic loading and unloading. Energy Science & Engineering (2022).