Deterministic cascade evolution in coal and gas outbursts: From early acoustic signatures to system-wide failure

Abstract

Coal and gas outbursts constitute a critical hazard in underground mining operations, characterized by rapid transitions from localized instability to catastrophic failure. Understanding the relationship between initial characteristics and final outburst scale remains a fundamental challenge in geomechanics. This study conceptualizes outbursts as deterministic cascade systems through integrated physical simulations combining high-sensitivity infrasound monitoring with energy analysis under controlled gas pressure (0.5–1.0 MPa) and confining stress (5–10 MPa) conditions. Our complementary analytical algorithms—the absolute amplitude integral and predominant period function—revealed characteristic step-wise patterns in outburst development. Quantitative analysis established a robust correlation (R2=0.91) between initial acoustic response and final outburst intensity. Energy analysis demonstrated that gas expansion dominates the outburst process (91.81%–99.09% of total energy), with desorption gas contributing 59.1%–77.7%. Time-frequency analysis showed systematic frequency migration from high (12–15 Hz) to low (4–8 Hz) bands during outburst progression, reflecting hierarchical spatial scale expansion. The concentrated energy release (>20% of total) within initial 0.2 s provides a mechanistic basis for the deterministic nature of outburst evolution. These mechanistic insights establish a quantitative framework for developing physics-based monitoring protocols and risk assessment methodologies applicable to underground coal mining operations.

1. Introduction

Do small and large coal-gas outbursts undergo different initiation processes? This fundamental question underlies our understanding of catastrophic failures in underground mining, where rapid transitions from localized instability to system-wide failure occur within seconds [1–3]. Although extensive research has established gas-driven eruption as the primary mechanism, the relationship between initial characteristics and final outburst scale remains poorly understood [4–6]. Current understanding of rapid failure transitions in geomaterials centers on two fundamental conceptual frameworks: the continuous growth model [7–9] and the cascade model [10]. The continuous growth model, derived primarily from laboratory observations, suggests smooth transitions from initial instability to final failure [11–13]. However, field observations of outburst characteristics and their power-law size distribution indicate significant self-similarity, suggesting that failure evolution may follow more complex patterns [14,15].

The widely accepted spherical shell destabilization model [9] for outbursts and the cascade model [16–18] in earthquake dynamics share a crucial insight: both phenomena exhibit hierarchical development through characteristic structures across different scales. When localized instability initiates, the subsequent evolution depends critically on the interaction between energy release and surrounding conditions [1,19]. In outbursts, gas expansion energy drives the process, with continuous gas desorption from coal matrix sustaining progressive failure development [20–22]. This mechanism differs fundamentally from earthquakes, where stored strain energy accumulated through tectonic loading governs the failure process [17,23,24]. Yet, despite these distinct energy sources, both systems demonstrate how microscopic instabilities can evolve into system-wide failures through similar cascade mechanisms. This mechanistic parallel offers valuable insights into understanding rapid failure transitions. The earthquake cascade model has demonstrated how initial rupture