Microseismic monitoring and forecasting of dynamic disasters in underground hydropower projects in southwest China:A review

The underground hydropower projects in Southwest China is characterized by large excavation sizes,high geostresses,complicated geological conditions and multiple construction processes.Various disasters such as collapses,large deformations,rockbursts are frequently encountered,resulting in serious casualties and huge economic losses.This review mainly presents some representative results on microseismic(MS)monitoring and forecasting for disasters in hydropower underground engineering.First,a set of new denoising,spectral analysis,and location methods were developed for better identification and location of MS signals.Then,the tempo-spatial characteristics of MS events were analyzed to understand the relationship between field construction and damages of surrounding rocks.Combined with field construction,geological data,numerical simulation and parametric analysis of MS sources,the focal mechanism of MS events was revealed.A damage constitutive model considering MS fracturing size was put forward and feedback analysis considering the MS damage of underground surrounding rocks was conducted.Next,an MS multi-parameter based risk assessment and early warning method for dynamic disasters were proposed.The technology for control of the damage and deformation of underground surrounding rocks was proposed for underground caverns.Finally,two typical underground powerhouses were selected as case studies.These achievements can provide significant references for prevention and control of dynamic disasters for underground engineering with similar complicated geological conditions.

A process-oriented approach for identifying potential landslides considering time-dependent behaviors beyond geomorphological features

Geomorphological features are commonly used to identify potential landslides.Nevertheless,overemphasis on these features could lead to misjudgment.This research proposes a process-oriented approach for potential landslide identification that considers time-dependent behaviors.The method integrates comprehensive remote sensing and geological analysis to qualitatively assess slope stability,and employs numerical analysis to quantitatively calculate aging stability.Specifically,a time-dependent stability calculation method for anticlinal slopes is developed and implemented in discrete element software,incorporating time-dependent mechanical and strength reduction calculations.By considering the time-dependent evolution of slopes,this method highlights the importance of both geomorphological features and time-dependent behaviors in landslide identification.This method has been applied to the Jiarishan slope(JRS)on the Qinghai-Tibet Plateau as a case study.The results show that the JRS,despite having landslide geomorphology,is a stable slope,highlighting the risk of misjudgment when relying solely on geomorphological features.This work provides insights into the geomorphological characterization and evolution history of the JRS and offers valuable guidance for studying slopes with similar landslide geomorphology.Furthermore,the process-oriented method incorporating timedependent evolution provides a means to evaluate potential landslides,reducing misjudgment due to excessive reliance on geomorphological features.

深部原位应力环境钻进过程中岩心饼化成因机制:数值模拟与室内试验

深部岩体原位应力赋存状态一直是“黑箱”问题,基于岩心的应力测试技术已成为有效的解决手段之一。在深部原位应力环境钻进过程中时常出现岩心饼化现象,为了探索其在砂岩中的形成机制,利用PFC2D研究了不同原位应力条件下钻进过程中的裂纹分布和能量演化,获得了易发生岩心饼化的特定原位应力条件。应用自主开发的测试系统验证了实验室环境内岩心饼化所需的应力条件,并分析了岩心破裂特征、断面形貌与原位应力之间的关系。结果表明,原位应力越高,在钻进过程中岩石产生的拉裂纹越多,尤其是在孔壁和岩心根部,而岩心处裂纹从外表面向内部发展。更高的原位应力水平同样会导致更强的能量转换,进而引发岩石破裂。岩心饼化的形成需满足特定的应力条件。当径向应力(σ_(r))为最大主应力且保持45 MPa恒定、轴向应力(σa)为25 MPa或30 MPa时,岩心根部均会发生饼化现象。随着σ_(r)和σa之间差值或钻进深度的增加,岩心厚度减小,导致断面更光滑、分形维数更小,从而使岩心饼化现象更加显著。该研究可为科学阐明深部原位应力条件下岩心饼化的形成机制提供必要的技术和数据支持。

高地应力地下厂房洞室群开挖卸荷围岩力学响应与稳定性分析

为了研究中国西南地区双江口水电站高地应力地下厂房洞室群开挖卸荷围岩力学响应与稳定性,构建高精度微震监测系统,并采用离散元法开展数值模拟。分析了开挖卸荷引起的围岩时空损伤特征,研究了高地应力与结构面共同控制下围岩塌方形成过程微震震源参数演化规律。建立了地下厂房洞室群三维离散元数值模型,揭示了开挖卸荷引起的围岩变形特征。研究结果表明,高地应力地下厂房洞室群开挖卸荷引起的微震事件活动频繁,主厂房大桩号顶拱区域围岩损伤严重;在塌方发生前,微震事件数量和累积能量释放快速增长,视应力陡增之后出现下降,剪切以及混合型式的微破裂数量和占比显著增加;地下洞室最大位移基本位于拱肩区域。微震监测数据和数值模拟结果显示出较好的一致性,可为高地应力地下厂房洞室群围岩损伤评估和灾害预警提供重要参考。

Discrete element method study of hysteretic behavior and deformation characteristics of rockfill material under cyclic loading

Granular geomaterials under different loading conditions manifest various behaviors,such as hysteresis.Understanding their hysteretic behavior and deformation characteristics is the basis for establishing a constitutive relation with excellent performance in deformation prediction.The deformation characteristics of crushable particle materials are analyzed through a series of cyclic loading tests conducted by numerical simulation.The hysteretic behavior is investigated from a particle scale.The increase in particles with contacts less than two may be responsible for the residual strain,and the particle breakage further promotes particle rearrangement and volume contraction.Both the accumulation of plastic strain and the resilient modulus are found to be related to confining pressures,stress levels,cyclic loading amplitudes,and the number of cycles.The plastic strain accumulation can be written as a function of the number of cycles and an evolution function of resilient modulus is proposed.

Optimization of Solid-Phase Extraction Conditions for Perfluorooctanoic Acid in Leachate

In order to optimize the solid phase extraction(SPE)conditions of perfluorooctanoic acid(PFOA)in the raw leachate and treated leachate,the effects of activator properties,SPE cartridge,p H value,ionic strength,and eluent properties were studied through single factor experiments.The optimal results of each single factor were obtained.Considering that the concentration of PFOA in the treated leachate is lower than that of the raw leachate,the SPE conditions of the treated leachate have been further optimized.Based on the above single-factor experiment,the main influencing factors were screened out as the volume of activator,ionic strength,and volume of eluent,and the three-factor threelevel response surface methodology(RSM)was optimized.The optimum SPE conditions of PFOA from treated landfill leachate were as follows:Activation of weak anion exchange(WAX)cartridge with 10 mL methanol,dosage of 600 mg KCl,6 m L 1%ammonia methanol eluted PFOA,the theory recovery rate is over95.67%.It has been verified that the error between the predicted value and the actual extraction recovery is small and has good repeatability.

The damage evolution behavior of polypropylene fiber reinforced concrete subjected to sulfate attack based on acoustic emission

To study the damage evolution behavior of polypropylene fiber reinforced concrete(PFRC)subjected to sulfate attack,a uniaxial compression test was carried out based on acoustic emission(AE).The effect of sulfate attack relative to time and fiber hybridization were analyzed and the compression damage factor was calculated using a mathematical model.The changes to AE ringing counts during the compression could be divided into compaction,elastic,and AE signal hyperactivity stages.In the initial stage of sulfate attack,the concrete micropores and microcracks were compacted gradually under external load and a corrosion products filling effect,and this corresponded with detection of few AE signals and with concrete compression strength enhancement.With increasing sulfate attack time,AE activity decreased.The cumulative AE ringing counts of PFRC at all corrosion ages were much higher than those for plain concrete.PFRC could still produce AE signals after peak load due to drawing effect of polypropylene fiber.After 150 d of sulfate attack,the cumulative AE ringing counts of plain concrete went down by about an order of magnitude,while that for PFRC remained at a high level.The initial damage factor of hybrid PFRC was-0.042 and-0.056 respectively after 150 d of corrosion,indicating that the advantage of hybrid polypropylene fiber was more obvious than plain concrete and single-doped PFRC.Based on a deterioration equation,the corrosion resistance coefficient of hybrid PFRC would be less than 0.75 after 42 drying-wetting sulfate attack cycles,which was 40%longer than that of plain concrete.