Displacement, stress and seismicity in roadway roofs during mining-induced failure

Roof stability in gateroads is a long-standing issue in many of the underground mines in Australia that use longwall extraction methods, due primarily to a significant increase of vertical stresses ahead of the longwall face. Although numerous studies have been done in the past, the process of roof rock deformation and breakage prior to and during a roof failure in an actual mining environment is still being debated. This paper describes a new integrated roof monitoring system and the results from applying this system in an Australian underground coal mine. The system integrates displacement, stress and seismic monitoring. It has been applied to two roadways in an Australian underground coal mine during two field experiments. The key roof behaviour identified by the integrated monitoring package during the two field monitoring experiments is reported and discussed in this paper.The experiments were conducted in the “tailgate” roadways that are adjacent to the caved zone, or “goaf”, of the previously mined panels. It was found in the experiments that, prior to roof falls, roof displacement accelerates whereas the horizontal stresses reduce. Seismic activity intensifies before major roof displacement or stress changes are evident, and subsides in the later stage of roof failure when large roof displacement is visible. The seismic resonance frequencies decrease during roof failure development. The field monitoring studies have also identified a number of quantitative and site-specific roof fall precursors potentially useful for roof fall prediction and prevention.     

Anatomy of mining-induced fault slip and a triggered rockburst

Fault slips and triggered rockbursts pose a significant threat to the safety of mining personnel and infrastructure in deep coal mines. Sudden and dynamic slip may occur along a pre-existing fault characterized by the presence of contact between two opposite faces. Such slips are capable of changing the balance of forces when mining activity is conducted in the area surrounding the fault at depth and are accompanied by energy release that has the potential to cause serious damage to roadways and working faces. The aim of the comprehensive investigation reported here was to elucidate the evolution of the stress field surrounding a fault due to mining activity in adjacent working faces, using Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) numerical simulations, especially variations the high shear stress area. We then proposed the mining-induced fault slip mechanism. The evolution rule of sources during fault slip could be clearly explained using field microseism (MS) monitoring data, and the correlation between source parameters (e.g., static stress drop, peak particle velocity, and displacement) and fault slip was established. Correspondingly, the multi-parameter precursors of a rockburst induced by the fault slip were analyzed and summarized in detail. This work provides a number of reference points to be used for the warning and controlling of rockbursts triggered by fault slip in coal mines.

     

Influence of fault slip on mining-induced pressure and optimization of roadway support design in fault-influenced zone

This paper presents an investigation on the characteristics of overlying strata collapse and mininginduced pressure in fault-influenced zone by employing the physical modeling in consideration of fault structure.The precursory information of fault slip during the underground mining activities is studied as well.Based on the physical modeling,the optimization of roadway support design and the field verification in fault-influenced zone are conducted.Physical modeling results show that,due to the combined effect of mining activities and fault slip,the mining-induced pressure and the extent of damaged rock masses in the fault-influenced zone are greater than those in the uninfluenced zone.The sharp increase and the succeeding stabilization of stress or steady increase in displacement can be identified as the precursory information of fault slip.Considering the larger mining-induced pressure in the fault-influenced zone,the new support design utilizing cables is proposed.The optimization of roadway support design suggests that the cables can be anchored in the stable surrounding rocks and can effectively mobilize the load bearing capacity of the stable surrounding rocks.The field observation indicates that the roadway is in good condition with the optimized roadway support design.     

Vibrations induced by high initial stress release during underground excavations

Excavation unloading under high initial stress is a typical dynamic process subjected to the combined effects of different factors. In this study, a mathematical physics method for a two-dimensional circular excavation was developed to investigate the mechanism involved in unloading vibration, which is capable of providing insights into the quantitative relationships between vibration features and correlative factors such as the initial stress, cross-sectional area of the tunnel, unloading rates and unloading paths. Then the dynamic unloading excavation process was implemented in the discrete element program PFC 2D for numerical analysis after verifications against the theoretical results. In particular, the characteristics of unloading waveform under high initial stress were investigated for various ratios of horizontal and vertical in situ stresses and aspect ratios of rectangular tunnels. The temporal and spatial characteristics of the excavation process can also be illustrated. In a practical project which considered the combined action of both the blast and unloading vibration, the finite difference program FLAC 3D was further adopted to investigate the contribution of unloading vibration to the character of the seismogram. Results are presented which indicate the 2D numerical analysis provides satisfactory approximation to the excavation process. While the peak particle velocity (PPV) is in direct proportion to the in situ stress variation, it decreases significantly along with the increase of unloading time. In addition, excavation by drill-and-blast (D&B) method should be taken as a dynamic process of blast loading before unloading in a period of time, instead of instantaneous unloading. Although unloading vibration can be generated and significant damage around the tunnel can be induced in the process, distinct unloading vibration can only be generated under high in situ stress and unloading rate.     

强夯的边界接触应力与沉降特性研究

在考虑夯锤自重的基础上，结合夯锤的刚体运动方程和成层弹性地基空间轴对称动力问题的传递矩阵法，导出了强夯的边界接触应力与沉降在变换域中的解析式，通过Ｌａｐｌａｃｅ－Ｈａｎｋｅｌ联合反变换求得了边界接触应力与沉降的时程关系，确定了接触应力时间，并将计算和实测结果作了比较。本文方法能反映强夯的实际性状，有利于成层地基强夯机理的数值分析工作。     

Mercury storage in surface soils in a central Washington forest and estimated release during the 2001 Rex Creek Fire

Recent investigations indicate that wildfires provide a significant flux of mercury (Hg) from terrestrial ecosystems to the atmosphere. However, little is known about how geographic location, climate, stand age, and tree species affect Hg accumulation prior to burning and loss during burning. Soil cores collected in sites burned during the summer 2001 Rex Creek Fire in the eastern Cascade Mountains (Washington State, USA) and in adjacent unburned control sites indicate that Hg loss from soils during the Rex Creek Fire averaged 6.7 (+/-2.5) g Hg ha(-1). This soil profile-based estimate of Hg release is higher than a previous estimate for the same fire based on airborne measurements of Hg and CO concentrations in smoke. This study has implications for global estimates of Hg storage in forests and release to the atmosphere during wildfires.     

西安某大厦供热初期风机盘管冻裂故障分析

指出造成该工程供热初期风机盘管冻裂事故的主要原因在于脏堵、气堵及室外空气温度和建筑朝向等因素。     

Instantaneous lighting quality within higher educational classrooms in Singapore

This paper presents a field study that explores lighting qualities within higher educational classrooms in Singapore. Eight classrooms of three types—computer labs, collaborative learning spaces and lecture halls—are studied. Lighting simulation models are calibrated and validated by measurements taken onsite and utilized to generate both instantaneous and annual physical lighting data. A questionnaire survey is distributed to 333 participants to gather subjective responses to current lighting perception. The results show that electrically lit lecture halls present more uniform distributions of lighting environments, while daylit computer labs and daylit collaborative learning spaces present relatively lower daylighting conditions. For daylit computer labs, horizontal illuminance is an effective predictor in terms of controlling lighting levels; For electrically lit lecture halls, the mean luminance of the horizontal 40° band is an effective predictor in terms of subjective lighting comfort.     

考虑卸荷应力路径的深部采空区失稳局部能量释放判别准则

 对采空区形成过程中围岩应力路径特征进行分析,并对卸荷荷载进行求解。基于深部开采应力卸荷机制,以程潮铁矿为工程背景,建立深部采空区卸荷失稳分析模型,引入局部能量释放率指标对采空区卸荷过程中能量演化规律进行分析,并基于尖点突变理论建立了围岩失稳局部能量判别准则。研究表明,随着开采的进行,采空区围岩局部能量释放能呈4次多项式增长,增加速率逐渐增加;局部能量突变判别值计算表明,最终采空区系统处在稳定状态,虽然底部结构中的塑性区体积最大,但其对应的单位体积局部能量释放率相对较小,说明相对稳定性较好。局部能量释放率分布云图表明,水平方向上以能量释放为主,垂直方向上以能量集中为主,符合深部开采特征。综上所述,深部卸荷力学模型能有效体现采空区形成过程中围岩的稳定状态,局部能量释放率反应能量释放、转移及耗散等动态过程,为深部采空区稳定性研究提供了重要的参考。     

橡胶沥青应力吸收层在柔性路面中的应用

结合橡胶沥青应力吸收层在柔性路面中的应用,详细地阐述了橡胶沥青应力吸收层的施工工艺,并提出了相应的质量管理措施,以推广橡胶沥青在高速公路建设中的应用。     

高填路基盖板涵外界面受力状态形成机制研究

依据原位试验和数值模拟研究高填路基盖板涵外界面受力状态形成机制。结果表明:涵洞顶面压力大于上覆填土自重,呈非均匀分布形式,涵洞侧墙顶相对于顶板中部承受更大的压力,侧墙主要承担了来自两侧填土的附加压力;涵洞侧墙外水平压力远小于按土柱高度换算的静止土压力,涵洞地基的不均一地质条件导致涵洞单侧承受相对较大的水平力;涵土差异沉降导致涵洞体承担了大于上覆填土自重的压力,基底的不均匀沉降引起涵顶压力向一侧集中,侧墙外压力和基底压力非对称分布。实测涵顶压力约为填土自重应力的1.56~3.02倍,使用现行公路桥涵规范设计高填方盖板涵偏于危险。     

Irreversible membrane fouling during ultrafiltration of surface water

For more efficient use of membranes, the control of irreversible membrane fouling, which can be defined as fouling requiring chemical reagents to be mitigated, is of importance. In this study, irreversible fouling caused by constituents in surface water was investigated, based on a long-term pilot scale study. The membrane employed was a low-pressure hydrophobic ultrafiltration (UF) membrane made of polysulfone and having a molecular weight cutoff of 750,000 Da. Various chemical reagents were examined to overcome the irreversible fouling that had developed through 5 months of continuous filtration. Among the tested cleaning reagents, alkaline (NaOH) and oxidizing reagent (NaClO) showed good performance in the restoration of membrane permeability, which implied that organic matter played an important role in the development of the irreversible fouling in this study. Chemical analysis, adsorptive fractionation methods, fluorescence excitation-emission matrix (EEM) and Fourie-transformed infra-red (FTIR) spectra analysis were applied to elucidate which fraction of organic matter caused the irreversible fouling. All of the analysis indicated that polysaccharide-like organic matter was responsible for the evolution of the irreversible fouling. In addition to organic matter, presumably iron and manganese also contributed to the irreversible fouling to some extent.     

浅谈施工中楼面裂缝的分析与防治

结合多年来的施工实践经验和教训，指出现浇楼板设计中应重点加强的部位，从设计、施工、材料三方面出发，采取了一系列相应的技术措施，并精心组织施工管理，达到了有效控制混凝土楼面裂缝的目的。     

Analysis of stress evolution characteristics during TBM excavation in deep buried tunnels

Bulletin of Engineering Geology and the Environment - Full-face tunnel boring machines (TBMs) are widely used in tunnel engineering projects as an efficient, safe and economical tunneling method....     

Assessing fault reactivation tendency within and surrounding porous reservoirs during fluid production or injection

This paper investigates fault reactivation tendency within and surrounding reservoirs during fluid injection or production. Induced stress analysis is performed using Eshelby's theory of inclusions for a poroelastic material, and the concept of Coulomb failure stress change is implemented as a criterion for fault reactivation tendency. A methodology is developed to find the range of fault dip angles that tend towards reactivation in either thrust or a normal fault stress regimes. The results demonstrate that, during production from a reservoir in a normal fault stress regime, fault reactivation is likely to occur within the reservoir and adjacent to its flanks. For a thrust-fault stress regime, only faults located in rocks overlying and underlying the reservoir tend towards reactivation. The results for the analogous case of fluid injection are exactly the opposite. Sensitivity analyses show that the locations of the boundaries defining these regions of reactivation (or stabilization) tendency are not highly sensitive to the fault friction coefficient. The use of the proposed methodology is illustrated for a synthetic case study.     

施工期钻井井壁钢筋应力实测研究

介绍了温家庄铁矿副井钻井井壁施工期间钢筋应力的实测方案,分析了钻井井壁钢筋应力的变化规律,结果表明：施工期钻井井壁钢筋以受压为主,环向钢筋压应力大于竖向钢筋,钢筋应力变化阶段与施工工序相对应。漂浮下沉阶段钢筋应力呈现“双线性”特点,实测与理论计算应力相吻合;增加配重水阶段环向钢筋压应力减小而竖向钢筋压应力增加;首次注浆阶段钢筋压应力显著减小,个别钢筋出现拉应力;后 3 次注浆阶段钢筋压应力先增加后部分恢复,环向钢筋应力变化大于竖向钢筋;抽排配重水阶段环向钢筋压应力显著增加,竖向钢筋应力变化不大;二次补注浆阶段钢筋压应力先增加后恢复,但恢复幅度较前述注浆有所减小。施工完成后钢筋最大应力达到屈服应力的 41% 。     

Biosorption processes in biomembrane systems during water treatment of surface water sources

The characteristics of a system with bioactive powdered activated carbon and microfiltration have been studied under conditions of the aerobic treatment of natural water from the water storages of Guan Ting (China), the Moskva River, and the Yauza River (Russia). The removal of organic matter in the system was estimated in terms of the permanganate oxidizability and UV absorption at λ = 254 nm (UV₂₅₄) and λ = 410 nm (UV₄₁₀). The average removal efficiency amounted to 68.42, 75.61, and 87.50%, respectively, at water temperature 10°C. The water treatment process (at 20°C) began immediately after the start-up of the plant at the expense of the adsorption on activated carbon that guaranteed a high speed of removal of organic pollutants in the absence of mature microflora. By the time the adsorption capacity of carbon was exhausted, the microflora was able to mature ensuring in combination with the powdered activated carbon a high speed of removal. In order to guarantee the biological stability of water, the removal degree of assimilable organic carbon amounted to 60.2% and the purified water met the requirements of the recommended criterion (100 mg acetate-C/dm³).     

Impacts of blending ground, surface, and saline waters on lead release in drinking water distribution systems

The impacts of distribution water quality changes caused by blending different source waters on lead release from corrosion loops containing small lead coupons were investigated in a pilot distribution study. The 1-year pilot study demonstrated that lead release to drinking water increased as chlorides increased and sulfates decreased. Silica and calcium inhibited lead release to a lesser degree than sulfates. An additional 3-month field study isolated and verified the effects of chlorides and sulfates on lead release. Lead release decreased with increasing pH and increasing alkalinity during the 1-year pilot study; however, the effects of pH and alkalinity on lead release, were not clearly elucidated due to confounding effects. A statistical model was developed using nonlinear regression, which showed that lead release increased with increasing chlorides, alkalinity and temperature, and decreased with increasing pH and sulfates. The model indicated that primary treatment processes such as enhanced coagulation and RO (reverse osmosis membrane) were related to lead release by water quality. Chlorides are high in RO-finished water and increase lead release, while sulfates are high following enhanced coagulation and decrease lead release.     

Study on the influence of the fault dip angle on the stress evolution and slip risk of normal faults in mining

Bulletin of Engineering Geology and the Environment - To address the frequent occurrence of activation-induced rock bursts in fault zones during mining, the stress evolution and fault slip behavior...     

Involvements of stress triaxiality in the brittle fracture during earthquakes in steel bridge bents

Stress triaxiality is proposed as one of the key parameters to discuss the cause of brittle fracture during earthquakes in steel structures. This study analytically investigated the features of stress triaxiality in steel bridge bent subjected to earthquakes. The target structure is a steel bridge bent actually fractured during the South Hyogo prefecture Earthquake. From the investigations, it was confirmed that high stress triaxiality was generated at a point supposed as fracture origin. There is a possibility that the triaxiality was involved in the fracture strongly through the increase of maximum principal stress. Moreover, from the analyses accounting for several kinds of large earthquake waveforms, it was indicated that threre is possibility that the distribution of triaxiality around the fracture origin was not affected by significantly by each cycle and each waveform.