地下建筑物的扬压力计算

扬压力是影响建筑物特别是地下建筑物稳定的重要荷载。对于土基上的扬压力计算,传统算法是把建筑物基底面看作是扬压力的作用面,不考虑土体颗粒同基底面相接触而造成的扬压力的减小。对于黏性土地基,可以引入平面有效空隙率的概念,这样计算的基底扬压力值比常规算法的结果要小,从而可以在安全的前提下有效地节约工程投资。     

Discussion on the assessment of initial stress field of railway rock massEI北大核心

Research purposes: In actual work, according to the ground stress data for assessment, most railway tunnels are under very high ground stress and high ground stress state, which causes adjustment of surrounding rock and engineering measures to strengthen, thus these will cause large increased investment, even cause large dispute and chaos in analysis causes of tunnel lining cracking and deformation, but the engineering case that rock burst and large deformation occurred in actual excavation of tunnel is very rare. In this paper, according to rock mass mechanical theory, the ground stress information and engineering case, combined the relevant provisions of similar industry, the assessment of initial stress fields of rock mass in railway specification is discussed. Research conclusions: (1) The assessment of railway specification to initial ground stress field is not realistic and should be revised, preliminary judgment when the measured in-situ stress >30 MPa, the possibility of rockburst is increased. (2) Assessment conclusion of initial ground stress field should be discreet, the increased investment should be incorporated into the dynamic design. (3) The stress tests of survey design stage should be reasonable and appropriate. (4) The research results can be applied to the modification of railway norms and tunnel exploration.     

A study on seepage field in subgrade slope subjected to various rainfall patternsEI北大核心

Research purposes: Rainfall is one of the most important factors for subgrade slope failure, and rainfall patter is one of the most primary influence parameters. Based on the two-dimensional saturated-unsaturated seepage theory, numerical analyses are conducted to investigate the change rules of seepage field in subgrade slope subjected to rainfalls with four different patterns, i.e. delayed, uniform, central and advanced rainfall patterns. Research conclusions: (1) Both the maximum pore-water pressure umax and the maximum saturated depth Hsmax at shoulder are affected by rainfall intensity and rainfall duration observably. (2) There is a sensitive range of coefficient of permeability influencing on the maximum saturated depth, only within the sensitive range increasing coefficient of permeability could reduce Hsmax and subgrade surface pore-water pressure effectively. (3) Under central and advanced rainfall patterns, the most dangerous time stage of slope stability is obvious affected by coefficient of permeability, within the sensitive range and the less side outside the sensitive range, the starting point of the most dangerous time stage is not affected by coefficient of permeability, but the end time is advanced with coefficient of permeability increasing. (4) The stability of subgrade slope is the best under advanced rainfall pattern and the worst under delayed rainfall pattern. (5) The research results can provide basis and reference for slope protection and reinforcement design.     

大断面浅埋小净距隧道衬砌计算研究

通过对浅埋小净距隧道围岩压力的计算进行分析,得出隧道围岩压力的计算公式。以白山大断面小净距隧道为例,采用荷载结构法对隧道衬砌进行了检算,得出衬砌安全系数,并与规范值进行对比,以此评定隧道衬砌设计的合理性,对大断面浅埋小净距隧道的设计有一定的指导意义。     

封闭式连通管挠度测量系统动态特性研究

挠度的长期、自动、准确、快速测量一直是大跨度桥梁监测的重点和难点.在简要对比现有挠度监测方法的基础上,介绍了近年来兴起的封闭式连通管挠度测量系统,分析了其动态挠度测量的实现原理和量值传递过程,通过振动台试验测定了系统的动态特性.理论分析和试验结果表明,压力传感器的存在改变了管道的终端阻抗,显著影响了管道压力传递的动态特性;同时压力传感器较低的通频带可能会带来不可忽视的测量失真.针对这两个影响因素,讨论了提升系统动态特性的可行方法,并对系统的研究和改进方向提出了建议.     

基于流-固耦合的盾构隧道开挖面稳定性研究

利用FLAC3D建立三维数值模型,对考虑完全流-固耦合效应的盾构隧道开挖面失稳过程进行模拟和验证,并进一步分析水位高度、渗流时间对开挖面变形、地表沉降和孔隙水压力的影响。研究表明:开挖面变形随支护压力比的减小经历3个阶段的变化,且与土体塑性区的发展密切相关;相比于无水状态,考虑流-固耦合效应的开挖面稳定性显著降低,随水位的升高、渗流时间的增大,开挖面发生失稳破坏的支护压力比明显增大;支护压力比(表征支护压力)的减小将导致开挖面前方一定范围的孔隙水压力减小,靠近开挖面的孔隙水压力受扰动程度加剧,形成"漏斗状"的影响区;开挖面失稳导致土体位移场延伸至地表,引起地表产生明显的沉降变形,在不同的变形阶段开挖面中心点位移与最大地表沉降分别呈抛物线相关和线性相关。     

土压平衡盾构开挖面压力取值及对地表沉降的影响

土压平衡盾构广泛应用于地铁隧道施工中,其施工过程产生的地表沉降及相关问题直接影响隧道施工安全。以成都地铁3号线某区间盾构隧道工程为例,应用理论方法计算盾构开挖面压力取值范围。结合工程地质条件、施工参数、不同开挖面压力和地层损失率,利用嵌入了土应力路径本构模型的ABAQUS软件进行盾构开挖三维模拟,得到了卵石地层盾构施工引起的地表沉降规律,并通过与现场地表沉降监测结果对比,验证了此模型的合理性,确定了合理的开挖面压力取值范围。最后,进一步分析了实际盾构施工开挖面压力值与地表沉降值之间的规律,评价施工时设定的开挖面压力值的优劣。     

客渡轮主机“冒黑烟”原因分析及解决办法——江城800客位新型渡轮排气管改造

本文主要介绍了渡轮柴油主机冒黑烟现象,对主机各性能以及客渡船营运带来诸多不良影响,在查找主机冒黑烟原因的过程中,采取多种途径在各系统上进行测试分析.理论上确定了排气背压高是引起主机冒黑烟的真正原因后,为了验证这一结论,在实船上进行排气管改造.改造完工后完全解决了主机冒黑烟问题,主机运转情况良好,各性能指标均达到要求,并且主机油耗下降明显.     

国外海底管道局部屈曲研究综述

海底管道是海洋油气集输系统中最重要的组成部分之一,从铺设到服役都将承受多种载荷的作用,并可能发生局部屈曲且沿管道传播开来,由此造成严重的后果。海底管道的局部屈曲在管道安全性方面具有重要意义,已成为海底管道设计与评估中重要的内容。详细阐述了国外关于海底管道受外压、弯矩和轴力作用下的局部屈曲研究成果,论述了在单个载荷和多个载荷联合作用下的局部屈曲破坏机理,并提出了未来研究的建议。     

锥柱耐压壳典型焊接接头残余应力研究

高强度钢材料对焊接残余应力非常敏感,显著影响了高强度钢锥柱耐压壳结构的安全可靠性及使用寿命,有必要针对这类壳体典型焊接接头的残余应力进行分析研究。本文首先基于有限元软件ANSYS的参数化语言APDL开发相应的焊接模拟程序,对高强度钢锥柱耐压壳典型焊接接头模型的焊接过程进行数值模拟,得到其焊接残余应力的应力水平及分布规律;然后采用X射线无损检测方法测量焊缝区域的残余应力。结果显示：焊缝附近区域存在较大焊接残余应力,其值随着与焊缝中心线距离的增加而迅速降低,数值模拟结果与试验结果基本吻合。