地铁车站PBA工法施工技术研究

结合工程实例,针对暗挖地铁车站,主要阐述了暗挖工法的比选、PBA工法的特点、施工工序及地层沉降控制措施,为我国各大城市修建地铁车站时选择合理的施工方法提供了有益的指导。     

Telechelic polymers by living and controlled/living polymerization methods

Telechelic polymers, defined as macromolecules that contain two reactive end groups, are used as cross-linkers, chain extenders, and important building blocks for various macromolecular structures, including block and graft copolymers, star, hyperbranched or dendritic polymers. This review article describes the general techniques for the preparation of telechelic polymers by living and controlled/living polymerization methods; namely atom transfer radical polymerization, nitroxide mediated radical polymerization, reversible addition-fragmentation chain transfer polymerization, iniferters, iodine transfer polymerization, cobalt mediated radical polymerization, organotellurium-, organostibine-, organobismuthine-mediated living radical polymerization, living anionic polymerization, living cationic polymerization, and ring opening metathesis polymerization. The efficient click reactions for the synthesis of telechelic polymers are also presented.     

New challenges in polymer foaming: A review of extrusion processes assisted by supercritical carbon dioxide

It is well known that supercritical carbon dioxide (sc-CO₂) is soluble in molten polymers and acts as a plasticizer. The dissolution of sc-CO₂ leads to a decrease in the viscosity of the liquid polymer, the melting point and the glass transition temperature. These properties have been used in several particle generation processes such as PGSS (particles from gas saturated solutions).It is therefore highly likely that extrusion processes would benefit from the use of sc-CO₂ since the rationale of the extrusion processes is to formulate, texture and shape molten polymers by forcing them through a die. Combining these two technologies, extrusion and supercritical fluids, could open up new applications in extrusion.The main advantage of introducing sc-CO₂ in the barrel of an extruder is its function as a plasticizer, which allows the processing of molecules which would otherwise be too fragile to withstand the mechanical stresses and the operating temperatures of a standard extrusion process. In addition, the dissolved CO₂ acts as a foaming agent during expansion through the die. It is therefore possible to control pore generation and growth by controlling the operating conditions.This review focuses on experimental work carried out using continuous extrusion. A continuous process is more economically favourable than batch foaming processes because it is easier to control, has a higher throughput and is very versatile in the properties and shapes of the products obtained.The coupling of extrusion and supercritical CO₂ technologies has already broadened the range of application of extrusion processes. The first applications were developed for the agro-food industry 20 years ago. However, most thermoplastics could potentially be submitted to sc-CO₂-assisted extrusion, opening new challenging opportunities, particularly in the field of pharmaceutical applications.This coupled technology is however still very new and further developments of both experimental and modelling studies will be necessary to gain better theoretical understanding and technical expertise prior to industrial use, especially in the pharmaceutical field.     

Ultrasmall size FeNi Prussian blue analogue on rGO with accurate heteronuclear adsorption sites toward efficient electrochemical nitrogen fixation

The electrochemical NRR to produce ammonia under ambient conditions represents an attractive prospect in nitrogen fixation which can greatly ease the energy crisis and environmental pollution. However, suffering from awful N₂ activation results in low ammonia yield rate and Faradaic efficiency in electrochemical NRR. In this work, we devote to construct FeNi heteronuclear sites in FeNi-PBA with accurate coordination structure to facilitate N₂ activation employing a side-on configuration. Control experiments have verified N₂ activation on FeNi heteronuclear sites was enhanced compared with that on FeFe sites. Meanwhile, the particle size of PBA was decreased to boost active sites. FeNi-PBA nanocrystals with ultrasmall size (10 ± 2.8 nm) through microwave-assisted synthesis achieve an ammonia yield rate of 17.7 mg_NH3 g_cat.^?1 h^?1 and Faradaic efficiency of 27.5% at a bias of ?0.2 V (V vs. RHE) in 0.05 M H₂SO₄ solution. Faradaic efficiency achieved in this work well exceeds than that of most Fe based transition metal electrocatalysts.     

基于大直径盾构隧道扩挖地铁车站关键工况控制措施研究

 北京地铁14号线将台站基于大直径单洞双线盾构隧道采用PBA工法扩挖形成。以地铁将台站作为工程背景,根据实际施工工序,分析了PBA工法扩挖大直径盾构隧道建造地铁车站的关键工况。利用“地层-结构”相互作用有限元法,模拟开挖过程,着重研究了盾构隧道两侧中洞非对称开挖和两侧K管片非对称拆除这两个关键工况的结构体系受力转换规律。结果表明：由于两侧中洞的非对称开挖扣拱及两侧K管片的非对称拆除,导致中洞初期支护、管片以及中隔墙的应力分布呈现非对称状态;管片环的最大主应力由压应力变为拉应力;中洞拱部初期支护最大主应力出现在一侧的K管片拆除后;在中洞开挖阶段,中隔墙最大主应力出现在一侧中洞开挖后;在K管片拆除阶段,当一侧的K管片拆除后,中隔墙承受偏压,两侧的K管片均拆除后,中隔墙的偏压现象消失,此时中隔墙主应力最大。表明在两侧中洞非对称开挖和两侧K管片非对称拆除工况下,中隔墙承受明显的偏压。根据数值模拟结果和管片拆除试验段的中隔墙应变监测结果,针对“中洞支护参数、中洞开挖方法、K管片拆除方法”等设计方案进行了优化,以确保车站扩挖施工安全和车站结构安全。     

地铁车站PBA工法施工技术及沉降分析

针对北京地铁四号线宣武门车站地质条件、周边环境复杂,周边构筑物、管线多,群洞数量多等特点,采用PBA洞桩法施工。阐述小导洞超前支护及土方开挖、边桩施工、过盖板河施工、减小群洞效应施工措施及监控量测成果等,有效控制地表沉降,保证周边建筑物及地下管线的安全。     

原位接枝改性纳米二氧化硅/聚丙烯复合材料Ⅱ:性能测试

通过熔融共混过程中原位接枝的方法制得聚丙烯酸丁酯接枝改性纳米二氧化硅/ 聚丙烯(SiO₂-g- PBA/PP) 复合材料, 探讨了材料制备的最佳工艺条件, 研究了复合材料的机械性能、结晶性能、微观形貌以及动态黏弹行为。结果表明, 少量纳米粒子(体积分数≤1.36 %) 的加入即可对PP 起到同时增强增韧的作用, 制备SiO₂-g- PBA/PP 的适宜工艺条件为熔融共混温度180 ℃, 共混时间10 min , 转子转速60 r/ min。对复合材料结晶行为的研究表明, 纳米粒子的成核效应使PP 的结晶速率加快。微观形态观察表明, 纳米粒子与聚合物基体间具有良好的界面结合, 这一点从对材料动态黏弹行为的研究中得到进一步证明, 从而阐明了纳米粒子增韧增强聚合物的机理。     

地铁浅埋暗挖洞桩法车站扣拱施工技术

以北京地铁十号线工体北路站洞桩法(PBA)扣拱施工实际工程为依托,详细介绍了洞桩法(PBA)施工技术的优点,并对洞桩法(PBA)施工存在的边拱施工及导洞回填、初支扣拱、导洞间土体开挖、站厅板施工、二衬扣拱等具体技术环节进行了详尽的研究,以及对工体北路站洞桩法(PBA)扣拱施工技术要点进行了总结,同时对监测量控和质量控制要点进行了重点阐述,可供类似工程特别是类似土质地层大跨度隧道开挖施工借鉴和参考.     

PBA法非对称不均匀变形引起地表沉降规律研究

通过北京地铁某地铁车站的工程实践,研究了洞桩法(8导洞)工程从群洞开挖到扣拱期间的施工步序、工序转换和空间变形发展规律,综合分析了几何轴对称的车站结构断面在施工时差条件下导致的空间不均匀变形发展规律,对比工程数值模拟、实测数据,研究了 工法执行差异是引起"地层-结构"一体结构的空间不均匀空间变形的主要原因.经过对变形曲...     

一种高效的具有灵活属性证书状态校验机制的PBA方案

可信计算平台的远程二进制证明方案确保了该平台的完整性,通过这种方法平台可以向远程方证明其可信性.然而这种二进制证明方案却存在很多缺陷,其中一个主要问题就是泄露了关于平台的(软、硬件)配置信息,这导致很多隐私问题的出现,例如差别化服务及匿名性破坏等问题.因此针对在可信计算环境下传统二进制证明中所带来的平台配置信息泄露等问题,提出了一种新型的基于属性证明方案(property-based attestation, PBA).该方案具有属性证书状态校验机制灵活、方案整体计算代价小及随机预言模型下可证安全等特点.利用本地验证者撤销的技术,设计了方案的模型,定义了方案的安全性,给出了方案的具体构建,并在随机预言模型下对该方案进行了安全性证明,证明其满足正确性、证明不可伪造性及配置隐私性等安全性质.最后将提出的PBA方案与现有PBA方案在计算代价和证明值长度方面分别进行了比较,比较表明该方案同时具有实用、高效的特点.