Mechanical Properties of Water-Saturated Coal in Underground Reservoirs

Water saturation profoundly alters the mechanical behaviour of coal in underground reservoirs by reducing strength, stiffness and energy absorption capacity. When pore spaces are filled with water, the uniaxial compressive strength and elastic modulus decline, while brittleness and fracture susceptibility increase. Water-induced softening promotes transitions from tensile to tensile–shear failure modes, influences fragment size distribution and accelerates crack propagation under both static and dynamic loads. Fluid–solid coupling gives rise to complex interactions between seepage pathways and stress fields, affecting the stability of coal pillar dams, water-resisting barriers and surrounding rock. Such changes are critical for the design of safe underground water storage, coal mine reinforcement, reservoir gas extraction and rockburst prevention. Advances in microstructural imaging, acoustic monitoring and numerical modelling have elucidated the evolution of microcracks, energy dissipation and deformation mechanisms, providing a foundation for optimising pillar widths, injection strategies and early warning systems in water-rich coal seam environments.

Research from Nature Portfolio

Recent studies have applied fractal analysis to acoustic emission (AE) records during uniaxial compression of water-saturated coal samples. These experiments reveal five distinct loading stages—compaction, linear elastic, stable crack propagation, accelerating crack propagation and post-peak residual—each marked by characteristic AE energy patterns. Water saturation lowers peak stress, elastic modulus and dissipated energy, while increasing the complexity of microcrack networks. By tracking changes in the fractal dimension of AE time series, researchers have identified the onset of unstable macrofracturing, offering a sensitive indicator for imminent failure. This approach highlights the potential for real-time monitoring of dynamic hazards in underground reservoirs and contributes to the development of predictive models for coal and rockburst prevention under varying moisture conditions.

Mechanical Properties of Water-Saturated Coal in Underground Reservoirs publication trend

The graph below shows the total number of articles in mechanical properties of water-saturated coal in underground reservoirs across all publications each year (not limited to Nature Index journals).

Technical terms

Uniaxial Compressive Strength (UCS): Maximum axial stress a coal specimen can sustain before failure under one-dimensional compression.

Elastic Modulus: Ratio of applied stress to resulting elastic strain, indicating material stiffness in the linear deformation range.

Acoustic Emission (AE): High-frequency elastic waves emitted by rapid energy release during microcrack initiation and growth.

Brittleness Index: Dimensionless measure of a material’s propensity to fracture rather than deform plastically under stress.

Fractal Dimension: Numerical value characterising the complexity and self-similarity of spatial distributions, used in AE signal analysis.

Seepage-Stress Coupling: Interaction between pore-fluid flow and mechanical stress distribution within a saturated coal mass.

References

1. Experimental and numerical investigation on failure characteristics and mechanism of coal with different water contents. International Journal of Coal Science & Technology (2023).
2. Damage and Failure Evolution Mechanism for Coal Pillar Dams Affected by Water Immersion in Underground Reservoirs. Geofluids (2019).
3. Experimental Investigation of the Mechanical Failure Behavior of Coal Specimens With Water Intrusion. Frontiers in Earth Science (2020).
4. Time Effect of Water Injection on the Mechanical Properties of Coal and Its Application in Rockburst Prevention in Mining. Energies (2017).
5. Experimental Study on Damage and Failure of Coal‐Pillar Dams in Coal Mine Underground Reservoir under Dynamic Load. Geofluids (2021).
6. Investigation of the acoustic emission and fractal characteristics of coal with varying water contents during uniaxial compression failure. Scientific Reports (2023).
7. Failure Characteristics of the Water-Resisting Coal Pillar under Stress-Seepage Coupling and Determination of Reasonable Coal Pillar Width. Water (2023).