煤层注水是预防煤矿粉尘危害的主动性、治本性措施，也是防治瓦斯突出、冲击地压等灾害的重要手段之一。但我国大量煤层具有高地应力、低孔隙率、低渗透性的特点，传统方法和技术面临水注入难、注水周期长、煤体假性润湿等瓶颈。为此，利用液态CO₂具有的低温冷冻、高渗透性、相变自增压、酸化解堵等优异特性，提出液态CO₂−水循环作用致裂增润煤体的新思路，研制了液态CO₂循环冷浸试验系统，联合低场核磁共振仪研究了液态CO₂−水循环作用对煤孔隙结构的影响规律，联用电液伺服压力实验机探究了循环作用对煤体力学特性的改变机理，运用截齿破碎煤岩产尘试验系统研究了循环作用后煤体破碎过程的产尘特性。结果表明：液态CO₂−水循环作用使煤体有效孔隙度(${varphi _{{{mathrm{NF}}}}}$)增加，增幅与循环作用次数呈正相关，煤体内部束缚流体变少，自由流体增多，T₂截止值(T_2cutoff)随之降低，结合分形理论发现基于渗流孔隙的分形维数D_s具有明显的分形特征，煤体原生孔隙经历了“扩容”的过程，微裂隙与原始裂隙形成贯通，循环作用增强了有效渗流通道连通性，优化了煤的孔隙网络与渗流条件。随着循环次数的增加，煤的最大应力${sigma _{{mathrm{c}}}}$呈指数衰减至4.93 MPa，应变${varepsilon _{{mathrm{c}}}}$线性增加至2.29×10⁻²，煤的抗压强度减弱，变形能力增加，循环作用改变了煤基质间联结状态，产生的冻胀力对煤体施加挤压作用加剧了裂隙的扩展，脆性指数${B_5}$最大降幅为34.71%，显著减弱了煤体脆性，具有了更好的抗动载荷或冲击能力；煤体对外加能量的存储能力弱化，改变了煤在截割过程中的破坏形式，试验条件下煤体破碎过程全尘产尘率降低了74%，呼吸性粉尘占比下降至2%，大幅减弱了粉尘危害性。

Coal seam water injection is a proactive and curative measure to prevent coal mine dust hazards and also one of the essential means to prevent and control gas protrusion, impact ground pressure, and other disasters. However, many coal seams in China are characterized by high ground stress, low porosity, and low permeability, and the traditional methods and techniques face some bottlenecks such as complex water injection, long water injection cycle, and pseudo-wetting of coal. To this end, using liquid CO₂ with excellent characteristics such as low-temperature freezing, high permeability, phase change self-pressurization, acidification, and unblocking, the authors put forward a new idea of fracturing and wetting coal by liquid CO₂-water circulation, developed an automatic control test system of cold dipping by liquid CO₂ circulation. The influence law of liquid CO₂-water cycling on the pore structure of coal was investigated using low-field nuclear magnetic resonance (LF-NMR) instrumentation, and the mechanism of change in the physical properties of coal by cyclic action was investigated using an electro-hydraulic servo-pressure experimental machine. The dust production characteristics of cyclic action on the coal crushing process were investigated using the coal rock-cutting dust production experimental system. The results show that the liquid CO₂-water circulation increased the effective porosity (${varphi _{{mathrm{NF}}}} $) of the coal, and the increase was positively correlated with the number of circulations. The bound fluid inside the coal become less, the free fluid increased, and the T_2cutoff value decreased. Combined with the fractal theory, it was found that based on the fractal dimensionality, D_s of seepage porosity had prominent fractal characteristics. The primary pores of the coal underwent the “enlargement” process. Microfracture and original fracture formed a through, and the circulation increased the connectivity of the effective seepage channel and optimized the coal’s porosity network and seepage conditions. With the increase in the number of cycles, the coal’s maximum stress value (${sigma _{mathrm{c}}} $) decayed exponentially to 4.93 MPa and the strain value (${varepsilon _{mathrm{c}}} $) increased linearly to 2.29%, the compressive strength of the coal weakened, the deformation capacity increased, the cyclic action changed the state of the coal matrix interconnection, and the resulting freezing and expansion forces exerted extrusion on the coal exacerbated the expansion of the fissures, and the brittleness index B₅ decreased by the maximum amount of 34.71%, which significantly weakened the brittleness of coal, and had a better resistance to dynamic load or impact. The weakening of the storage capacity of the coal body for the applied energy changed the form of coal destruction in the cutting process, and the whole dust production rate of the coal body cutting under the test conditions of this paper was reduced by 74%. The percentage of respiratory dust was reduced to 2%, drastically weakening the dust’s hazardousness.