Acoustic emission monitoring of rockbursts during TBM-excavated headrace tunneling at Jinping Ⅱ hydropower station

To better understand the mechanical properties of marble at Jinping II hydropower station, this paper examines the changes of brittle rocks in excavation damaged zones(EDZs) before and after excavation of tunnel with the tunnel boring machine(TBM). The paper attempts to employ the acoustic emission(AE) to study the AE characteristics and distribution of rockburst before and after TBM-excavated tunnel. It is known that the headrace tunnel #2, excavated by the drill-and-blast(D&B) method, is ahead of the headrace tunnel #3 that is excavated by TBM method. The experimental sub-tunnel #2–1, about 2000 m in depth and 13 m in diameter, between the two tunnels is scheduled. In the experimental sub-tunnel #2–1, a large number of experimental boreholes are arranged, and AE sensors are installed within 10 m apart from the wall of the headrace tunnel #3. By tracking the microseismic signals in rocks, the location, frequency, quantity, scope and intensity of the microseismic signals are basically identifed. It is observed that the AE signals mainly occur within 5 m around the rock wall, basically lasting for one day before tunnel excavation and a week after excavation. Monitoring results indicate that the rockburst signals are closely related to rock stress adjustment. The rock structure has a rapid self-adjustment capacity before and after a certain period of time during tunneling. The variations of rock stresses would last for a long time before reaching a fnal steady state. Based on this, the site-specifc support parameters for the deep tunnels can be accordingly optimized.

Image charge effect on the light emission of rutile TiO2(110) induced by a scanning tunneling microscope

The plasmon-enhanced light emission of rutile TiO2（110） surface has been investigated by a low-temperature scanning tunneling microscope （STM）. We found that the photon emission arises from the inelastic electron tunneling between the STM tip and the conduction band or defect states of TiO2（110）. In contrast to the Au（111） surface, the maximum photon energy as a function of the bias voltage clearly deviates from the linear scaling behavior, suggesting the non-negligible effect of the STM tip on the band structure of TiO2. By performing differential conductance （dl/dV） measurements, it was revealed that such a deviation is not related to the tip-induced band bending, but is attributed to the image charge effect of the metal tip, which significantly shifts the band edges of the TiO2（110） towards the Femi level （EF） during the tunneling process. This work not only sheds new lights onto the understanding of plasmon-enhanced light emission of semiconductor surfaces, but also opens up a new avenue for engineering the plasmon-mediated interfacial charge transfer in molecular and semiconducting materials.

Enhanced photon emission by field emission resonances and local surface plasmon in tunneling junction

We investigated the photon emission spectra on Ag(111)surface excited by tunneling electrons using a low temperature scanning tunneling microscope in ultrahigh vacuum.Characteristic plasmon modes were illustrated as a function of the bias voltage.The one electron excitation process was revealed by the linear relationship between the luminescence intensity and the tunneling current.Luminescence enhancement is observed in the tunneling regime for the relatively high bias voltages,as well as at the field emission resonance with bias voltage increased up to 9 V.Presence of a silver(Ag)nanoparticle in the tunneling junction results in an abnormally strong photon emission at the high field emission resonances,which is explained by the further enhancement due to coupling between the localized surface plasmon and the vacuum.The results are of potential value for applications where ultimate enhancement of photon emission is desired.

Wind tunnel experiments on dust emissions from different landform types

The measurement and assessment of dust emissions from different landforms are important to understand the atmospheric loading of PM10 （particulate matter ≤10 μm aerodynamic diameter） and to assess natural sources of dust; however, the methodology and technique for determining the dust still present significant research challenges. In the past, specialized field observation and field wind tunnel studies have been used to understand the dust emission. A series of wind tunnel tests were carried out to identify natural sources of dust and measure the magnitudes of dust emissions from different landforms. The method used in this study allowed the measurement of the PM10 emission rate using a laboratory based environmental boundary layer wind tunnel. Results indicated that PM10 emissions demonstrated strong temporal variation and were primarily driven by aerodynamic entrainment. Sand dunes, playa, and alluvial fans had the largest dust emission rates （0.8-5.4 mg/（me.s）） while sandy gravel, Gobi desert and abandoned lands had the lowest emission rates （0.003-0.126 mg/（m2.s））. Dust emissions were heavily dependent on the surface conditions, especially the availability of loose surface dust. High dust emissions were a result of the availability of dust- particle materials for entrainment while low dust emissions were a result of surface crusts and gravel cover. Soil surface property （surface crusts and gravel cover） plays an important role in controlling the availability of dust-sized particles for entrainment. The dust emission rate depended not only on the surface conditions but also on the friction velocity. The emission rate of PM10 varies as a power function of the friction velocity. Although dynamic abrasion processes have a strong influence on the amount of dust entrainment, aerodynamic entrainment may provide an important mechanism for dust emissions. Large volumes of dust entrained by aerodynamic entrainment cannot only occur at low shear velocity without saltation, but may dominate the entrainment process in many arid and semi-arid environments. So it may also be responsible for large magnitude dust storms. Playa and alluvial fan landforms, prior to developing a surface crust, may be the main sources of dust storms in Qinghai Province.

Properties of Light Emission Spectrumof Double-barrier Tunnel Junction

Fabricated are the double-barrier light emission tunnel junctions successfully. Introduced are the fabrication process and light emission characteristics. The spectra of the junctions are measured and analyzed especially. Their spectrum wavelength including main wave peak(locates at 450 nm^500 nm) of the double-barrier junction shows a "blue shift" in comparison with that of the single-barrier Metal/Insulator/Semiconductor(MIS) or Metal/Insulator/Metal(MIM) junction(wave peak locates at 620 nm^740 nm). This phenomenon should be due to the occurrence of the electron resonant tunneling in the double-barrier junction.

Fowler-Nordheim Tunneling, Photovoltaic Applications and New Band Structure Models of Electroconductive a-CNx:H Films Formed by Supermagnetron Plasma CVD

Hydrogenated amorphous carbon nitride (a-CNx:H) films were formed on Al films deposited on Si or glass (SiO2) substrates, using pulsed radio frequency (PRF) supermagnetron plasma (SMP) chemical vapor deposition (CVD) with N2/i-C4H10 mixed gases. a-CNx:H films were grown under the upper and lower electrode RF powers (13.56 MHz) of continuous and pulsed conditions, respectively, which showed low band gap of about 0.7 eV. a-CNx:H films deposited on the Al/Si or Al/SiO2 substrates showed same low threshold emission electric field (ETH) of 12 V/μm. Multiple layer of Al or ITO (anode)/50nm-SiO2/a-CNx:H/Al (cathode)/Si structures showed Fowler-Nordheim (FN) electron tunneling effect in both forward and reverse current directions. 12.5 nm a-CNx:H film on p-Si substrate showed a photoelectric conversion. Energy band structure and electron conduction models were proposed for the active states of both the field emission and FN tunneling devices and photovoltaic cells.

Experimental study on acoustic emission characteristics of jointed rock mass by double disc cutter

The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers have studied the interaction between TBM disc cutters and jointed rock mass.However,in most of these works,the effect of joint on rock fragmentation by double disc cutter has been scarcely investigated.Thus,the effects of joint orientation and joint space on rock fragmentation by double disc cutter are highlighted in this study.During the test,jointed concrete specimens are adopted to simulate jointed rock mass.Improved RYL-600rock shear rheological instrument was employed during the indentation process under disc cutters,and acoustic emission location system was used to analyze the rock damage and physical deterioration.The results show that there are four failure modes and three modes of crack initiation and propagation in jointed rock mass.It is concluded that the existing joint planes have obviously restrained the crack initiation and propagation during the rock fragmentation process.The results also indicate that samples are damaged most seriously when joint orientation equals60°,which is proved to be the optimum joint orientation in TBM penetration.

Problem of Nuclear Decay by Proton Emission in Fully Quantum Consideration: Calculations of Penetrability and Role of Boundary Conditions

We develop a new fully quantum method for determination of widths for nuclear decay by proton emission where multiple internal reflections of wave packet describing tunneling process inside proton-nucleus radial barrier are taken into account. Exact solutions for amplitudes of wave function, penetrability T and reflection R (estimated for the first time for decay problem) are found for n -step barrier (at arbitrary n) which approximates the realistic barrier. In contrast to semiclassical approach and two-potential approach, we establish by this method essential dependence of the penetrability on the starting point Rform in the internal well where proton starts to move outside (for example, for Ta the penetrability is changed up to 200 times;accuracy is T+R-1|-15 ). We impose a new condition: in the beginning of the proton decay the proton starts to move outside from minimum of the well. Such a condition provides minimal calculated half-life and gives stable basis for predictions. However, the half-lives calculated by such an approach turn out to be a little closer to experimental data in comparison with the semiclassical half-lives. Estimated influence of the external barrier region is up to 1.5 times for changed penetrability.

Field-assisted tunneling enabled pressure-sensitive composites/sensors for smart concrete structures

Spiky spherical nickel powder with sharp nano-tips on its surface is a kind of excellent fillers for developing pressure-sensitive cement-based composites/sensors for traffic detection,structural health monitoring,and border and military security.The sharp nano-tips on the surface of spiky spherical nickel particles can induce field emission and tunneling effects,which leads to the ultrahigh pressure-sensitive responses of the cement-based composites.In this paper,we systematically introduce research on nanotip-induced ultrahigh pressure-sensitive cement-based composites/sensors,with attentions to their pressure-sensitive property and sensing mechanism,pressure-sensitive characteristic model,and smart structure system for traffic detection.

Simulation Analysis of CO Concentration Distribution in Beijing Yuntong Tunnel

In this paper, the concentration distribution of CO emitted by motor vehicles in Beijing Yuntong Tunnel is simulated and analyzed based on Fluent numerical simulation software. Firstly, the physical model of tunnel geometry is established. Secondly, the suitable control equations and boundary conditions are selected to describe the diffusion distribution of pollutants in the tunnel. At the same time, the reliability of the model is verified according to the measured data, and the distribution law of CO concentration in the tunnel is observed through the simulation results. The tunnel is unorganized at the entrance of the tunnel. In the simulation results, the CO concentration at the entrance of the tunnel is far more than the CO unorganized emission limit in Beijing. The CO emission of the tunnel should be purified to prevent pollution of the urban environment.

新伊高速毗邻隧道遮阳棚光环境及降碳分析

为减少由光照强度差异引发的交通事故,以新伊高速公路工程为依托,在宋家凹—水沟河毗邻隧道连接段设置钢筋混凝土与钢结构组合形式的遮阳棚,计算限行速度下遮阳棚的长度,运用DIALux仿真软件对不同时间点下的2种工况进行研究,并采用碳排放因子法分析不同工况下的碳排放量。结果表明:该毗邻隧道连接段遮阳棚长度为100 m。设置遮阳棚后,路面照度降低率达到57.97%,照度总均匀度大于0.4,现场实测值与模拟值误差在10%范围内,均满足相关标准的要求。此外,设置遮阳棚后,每年减少碳排放量82.56 t CO_(2)e,运营2.8 a后可弥补建造时产生的碳排放,建设成本将在3.7 a后收回。在使用寿命期内,可减少碳排放量3 795.74 t CO_(2)e,节约成本577.31万元,实现了减排和节约成本的双重效果。

Wind tunnel simulation of wind erosion and dust emission processes,and the influences of soil texture

Dust emission caused by wind erosion of soil is an important surface process in arid and semi-arid regions.However,existing dust emission models pay insufficient attention to the impacts of aerodynamic entrainment of particles.In addition,studies of wind erosion processes do not adequately account for the dynamics of wind erosion rates and dust emission fluxes,or for the impact of soil texture on dust emission.Our wind tunnel simulations of wind erosion and dust emission showed that the soil texture,wind erosion duration,and shear velocity are major factors that affect the dynamics of wind erosion and dust emission.Because of the limited supply of surface sand and the change in surface erosion resistance caused by surface coarsening during erosion,the wind erosion rate and the flux of particles smaller than 10μm(PM_(10))caused by aerodynamic entrainment decreased rapidly with increasing erosion duration,which suggests that surface wind erosion and dust emission occur primarily during the initial stage of wind erosion.The PM_(10) emission efficiency decreased with increasing shear velocity following a power function,and finer textured sandy loam soils had greater PM_(10) emission efficiency than loamy sand soils.

基于LCA的山岭隧道碳排放核算研究现状与展望

首先,梳理山岭隧道碳排放核算研究的进展并进行探讨,基于生命周期评价理论(life cycle assessment,LCA)与排放因子法,结合山岭隧道特点对其全生命周期内各阶段的碳排放来源进行分析,着重探讨施工与运营阶段的计算边界;其次,强调碳排放核算过程中清单分析涉及到的碳排放因子与活动数据的获取方式与应用条件;然后,对核算结果的应用、不确定分析与碳排放预测的相关研究成果进行整理;最后,指出当前山岭隧道碳排放研究中存在的问题,并展望其未来发展方向。

铁路隧道工程节能减排技术研究现状及展望

考虑到铁路隧道工程的施工运营过程具有高能耗、高温室气体排放的特点,本文通过统计调研近10年来的相关文献,总结了目前常用的几种铁路隧道节能减排技术。从施工、运营两个方面介绍了铁路隧道所采用的节能技术:包括增大施工废渣回收利用率、利用可再生环保建材等绿色施工技术;应用智能控制系统和变频调速等方式降低风机能耗的节能通风技术;通过智能化控制灯具实现隧道按需照明的节能照明技术。

基准排放因子更新对隧道需风量的影响研究

为解决交通车辆持续更新导致的城市隧道内通风系统设计浪费和运营闲置,研究基准排放因子更新对隧道需风量的影响,并建立2种应对车辆更新的基准排放因子计算方法.首先,通过理论分析明确需风量计算式中随时间更新的关键参数为基准排放因子;随后,根据定量分析得到基准排放因子和纵坡-车速系数更新对需风量的影响;最后,结合国外理念和实际设计经验,提出2种考虑时间更新的基准排放因子计算方法.研究结果表明:我国道路隧道通风设计规范在制定基准排放因子时参考了世界道路协会(PIARC)通风报告,并分析得到了参考理由;与2000年相比,2021年的CO、NOx和PM基准排放限值分别降低了81.6%、76.7%和97.9%;建立了使用机动车污染物排放限值作为基准排放因子的最不利设计方法,计算出2018年各污染物基准排放因子(CO为0.0011 m^(3)/(辆·km),PM为0.4610 m^(2)/(辆·km)),相比于2014年《细则》分别降低84.3%和77.0%.建立并验证了基准排放因子计算方法,为城市道路隧道通风系统设计提供参考.

地铁施工物化阶段TBM区间碳排放核算与减排

目前,国内外对土建工程碳排放的研究主要集中在住宅、办公建筑领域,对地铁建设工程碳排放的研究较少。为计量地铁TBM区间土建工程物化阶段碳排放,识别其排放特点,运用碳排放系数法建立了包含TBM区间土建实体、建造配套设备、运输施工机具、周转材料、劳动力在内的系统边界,将物化阶段划分为建材及预构件生产、建材及预构件运输、现场施工三个环节对碳排放进行计量。对碳排放因子进行了定义选取,构建了TBM区间各环节碳排放的计量模型并对青岛地铁典型TBM工段进行了案例分析,得到物化阶段三个环节的碳排放强度分别为4875.87 tCO_(2)/km、49.54 tCO_(2)/km、1780.04 tCO_(2)/km,总碳排放强度为6705.45 tCO_(2)/km。通过情景假设法,得出地铁TBM区间再生建材的使用可以带来1.21%~2.43%的减排效益。

隧道工程建设碳排放特征与减碳潜力分析

为明晰隧道建设碳排放强度及贡献,指导隧道建设低碳转型,基于生命周期评价理论和排放因子法对公路隧道碳排放特征及不同情景下减碳潜力进行量化分析。研究结果表明:公路隧道建设碳排放强度平均值为3.437万t CO_(2)eq/km,材料生产、现场施工机械及场内材料转运碳排放贡献率分别为88.6%、9.2%和2.2%。碳排放来源主要集中于少数材料和机械,其中水泥、钢筋、冷轧带肋钢筋网、空气压缩机、自卸汽车、轴流式通风机、装载机需要进行重点管控。洞身开挖、洞身衬砌、仰拱、洞内路面碳排放强度较高需重点开展设计施工低碳优化,仰拱、洞身开挖碳排放强度与IV、V级围岩长度呈显著正相关。情景分析得到水泥低碳替代可减少1.83%~10.92%的材料生产碳排放,钢铁低碳替代可减少0.75%~5.99%的材料生产碳排放,电动化工程机械替代可减少3.48%~17.40%的场内运输碳排放和0.5%~2.53%的现场施工机械碳排放。

铁路隧道绿色低碳建造技术工程实践与展望

为实现铁路隧道全生命周期向绿色低碳方向发展,以京张高铁清华园隧道、新八达岭隧道和八达岭长城站为背景,采用数据统计分析的方法研究铁路隧道建设和运营阶段的碳排放,从隧道线位和车站站位选择、建筑、结构、通风、照明等方面提出隧道减碳设计策略。研究结果表明,减碳设计策略主要包括增加碳汇和减少碳排放2大类。增加碳汇的措施有:1)采用隧道下穿方案可减少地表土地占用,增加地表绿化面积;2)隧道洞口可采用绿色格宾挡墙和绿色植被覆盖来增加碳汇能力。减少碳排放的措施有:1)合理选择隧道线位和车站站位,减少乘客交通接驳;2)车站采用群洞设计方案可减少土石方开挖和支护措施工程量;3)超大跨隧道采用围岩自承载的设计理念和方法可减少衬砌混凝土用量;4)地下车站采用无空调活塞通风系统、光源智能管理及光纤照明系统、电梯等大型设备智能管理系统等可减少运营阶段的能源消耗。最后,提出绿色结构物建造、全预制精巧化结构研发、设备智能管控技术、铁路带状光伏发电场、压缩空气储能电站等绿色建造技术。

铁路隧道建造过程TBM施工碳排放量计算研究

随着国家“双碳”目标的提出,隧道工程施工碳排放核算至关重要。本文建立碳排放因子数据库,使用碳排放因子法编制隧道碳排放定额,建立铁路隧道TBM法开挖的碳排放量计算模型。根据LCA理论,将整个施工碳排放划分为建材生产、现场施工及建材运输三个阶段以进行相关计算,得出各阶段碳排放总量并分析各主要的碳排放量来源。结果表明:(1)TBM法隧道施工碳排放强度为173.593kgCO_(2)/m^(3),划分的三个阶段碳排放分别占比52.60%、44.44%、2.96%;(2)建材生产阶段主要碳源为钢材和水泥,现场施工阶段碳排放量主要来自盾构机、轴流通风机等电力机械。

Topologically engineering of π-conjugated macrocycles: Tunable emission and photochemical reaction toward multi-cyclic polymers

The topology of conjugated macrocycles had significant impacts on their photo-physical and photochemical properties.Herein,a series ofπ-conjugated macrocycles with diverse topology were synthesized via intramolecular McMurry coupling.Their chemical structure and macrocyclic topology were unambiguously confirmed via NMR,MALDI-TOF mass spectra,crystal analysis and scanning tunneling microscopy(STM).Depending on the structural topology and structural rigidity,these cyclic compounds display obviously distinctive emission behavior and photochemical reactions in the solution and in the solid state.Monocyclic phenylene vinylene macrocycle(denoted as MST)exhibiting aggregation-induced emission behavior,was more vulnerable to photo-cyclization in solution and triplet sensitizer promoted photodimerization due to lower strain and more flourishing intramolecular motions.After UV light irradiation,relatively more flexible MST could yield the anti-dimer via triplet excimer on the HOPG surface confirmed by STM investigation.By contrast,highly constrained bicyclic analogue(named as DMTPE)with central tetraphenylethene core,displayed high emission quantum yields of 68%both in solution and in the solid state,and was relatively inert to photochemical reactions and yield syn-dimer on the surface via singlet excimer involved[2+2]photo-dimerization.Based on the solution-mediated photo-polymerization of MST moiety,multicyclic porous carbon-rich ribbon connected with four-membered ring was successfully constructed and validated via STM imaging.