冻融作用下寒区半饱和砂岩强度衰减与能量演化机制

Mechanism of strength degradation and energy evolution of semi-saturated sandstone in cold regions under freeze-thaw action

摘要:

针对冻融作用下寒区边坡岩体强度衰减问题，以玉龙铜矿边坡青砂岩为研究对象，通过室内冻融循环、SHPB动态冲击试验和核磁共振孔隙分析，系统研究了半饱和砂岩在冻融作用下的动态力学劣化规律、能量演化特征及孔隙结构演化规律，并建立了基于能量反射率的冻融强度衰减模型。结果表明：随冻融次数增加，砂岩动态峰值应力由65.45 MPa降至51.8 MPa，劣化趋势呈现“先快后慢”的非线性特征；动态应力?应变曲线依次经历弹性阶段、应变软化阶段和快速卸载阶段，应变软化阶段随冻融次数增加逐渐缩短，并出现“应力跌落”与“应变回弹”现象；入射能与透射能总体上随冻融次数增加呈下降趋势，反射能在冻融20次时显著升高；高冻融次数促进了水分向较大孔隙迁移，使孔隙分布范围扩大，增强了介孔与大孔的响应特征。研究成果揭示了冻融循环作用下半饱和砂岩的损伤演化机制，为寒区边坡工程稳定性评价与防护设计提供了理论依据。

Abstract:

To address the strength degradation of slope rock masses in cold regions under freeze-thaw action， the bluish-grey sandstone from the Yulong Copper Mine slope was taken as the research object. Through indoor freeze-thaw cycles， SHPB dynamic impact tests， and nuclear magnetic resonance （NMR） pore analysis， the dynamic mechanical degradation laws， energy evolution characteristics， and pore structure evolution laws of semi-saturated sandstone under freeze-thaw action were systematically investigated， and a freeze-thaw strength degradation model based on absorbed energy was established. The results show that as the number of freeze-thaw cycles increases， the dynamic peak stress of sandstone decreases from 65.45 MPa to 51.8 MPa， exhibiting a nonlinear degradation trend of rapid initial decline followed by slow attenuation. The dynamic stress-strain curve sequentially undergoes an elastic stage， a strain-softening stage， and a rapid unloading stage. The strain-softening stage gradually shortens with increasing freeze-thaw cycles， accompanied by the phenomena of stress drop and strain rebound. Both incident energy and transmitted energy generally show a decreasing trend with increasing freeze-thaw cycles， whereas the reflected energy increases significantly at 20 freeze-thaw cycles. High freeze-thaw cycles promote the migration of moisture into larger pores， expand the pore distribution range， and enhance the response characteristics of mesopores and macropores. The research findings reveal the damage evolution mechanism of semi-saturated sandstone under freeze-thaw cycles， providing a theoretical basis for the stability evaluation and protection design of slope engineering in cold regions.