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31.
32.
随着地下空间资源的开发利用,越来越多深基坑呈现出开挖深、规模大、形状不规则等特点,其支护结构设计复杂,施工难度大,具有明显的空间效应。本文以南京地铁某基坑工程为例,分析基坑施工对邻近桥梁的影响。其场区位于长江下游漫滩相二元结构地层分布地段,上部软土层厚度大,下部承压含水层地下水位高、水量丰富,地质条件复杂,该基坑为典型的深大异形基坑,距离某大桥的双曲拱引桥仅为7. 2 m,由于之前桥梁已遭受其他地下工程施工产生的较大变形,所以后续工程对其影响变形控制要求极高。为此,该车站基坑支护结构设计基于地下空间实际功能采用设置分隔墙分区开挖及MJS超深工法墙综合变形控制方案。本文通过有限元数值模拟计算,开展复杂环境下基坑开挖引起的围护结构及桥梁桩基的变形预测分析,计算结果显示,该深大狭长异形基坑开挖对邻近桥梁沉降变形影响显著,通过设置分隔墙分区开挖及MJS工法墙进行变形控制,能够较好地控制基坑的空间效应,减少“长边效应”、“异形效应”等对桥梁沉降变形的影响。通过现场基坑开挖过程实际监测结果,验证这一综合变形控制方案的可行性。该研究成果对于类似复杂地质条件下深大狭长异形基坑的支护及施工设计具有很好的借鉴意义。 相似文献
33.
《水文科学杂志》2013,58(5)
Abstract Some unique coupled wind–water erosion processes exist in the desert-loess transitional zone in the middle Yellow River basin. Based on data from 40 stations on 29 rivers, a study was made on the influence of such processes on suspended sediment grain-size characteristics of the tributaries of the Yellow River. Results show that the percentage of >0.05-mm grain size decreases with the increased annual mean precipitation, but increases with the increase in the annual mean number of sand-dust storm days. The percentage of <0.01-mm grain size increases with the increase in the annual mean precipitation, but decreases with the increase in the annual number of sand-dust storm days. Based on annual mean data from 40 stations, multiple regression equations were established between the percentages of >0.05-mm grain size (r >0.05) and <0.01-mm grain size (r <0.01), annual mean precipitation (P m) and annual mean number of sand-dust storm days (D ss). On this basis, the relative contributions of the variations in D ss and P m to the variation in r >0.05 and r <0.01 were estimated. The results indicate that the variation in sand-dust storm frequency exerts greater influences on the variation in grain-size characteristics of suspended load than does the variation in annual mean precipitation. With the increase in the coupled wind–water processes index, expressed by P m/D ss, the percentage of >0.05-mm grain size in suspended sediment decreases and the percentage of <0.01-mm grain size increases. With the variation in P m/D ss, different combinations of r >0.05 with r <0.01 appear, which have some influence on the formation of hyperconcentrated flows. There exist some optimal ratios of coarse to fine fractions in suspended sediment that make sediment concentrations of hyperconcentrated flows the highest. The optimal r >0.05/r <0.01 value is related to some range of the index P m/D ss. When the P m/D ss index falls in this range, the optimum combination of relative coarse with fine sediments in the suspended load appears, and thus results in the peak values of sediment concentration. 相似文献
34.
本文通过具体工程实践,对在松散地基上兴建特大型公路桥梁的工程勘察要求、勘探工作布置、墩台基础持力层的选择及对地基评价作了分析、论述,可供同行借鉴与参考 相似文献
35.
笔者报告了23例化脓性脊柱炎。本文着重分析对比了X线平片和CT检查结果,通过分析对比,发现CT检查优于X线平片,并有助于对化脓性脊柱炎早期作出诊断。主要影像学表现:早期,软组织肿胀和脓肿形成,骨质呈虫蚀状破坏,随之破坏区周围出现增生硬化。CT 还能发现炎块中的气体。晚期,骨质修复占优势,即骨质增生硬化,骨桥形成,最后可产生骨性融合。 相似文献
36.
介绍了在浅海施工直径2.20m嵌岩桩的技术问题。包括平台的搭设,用刮刀钻头与牙轮钻头钻进克取硬岩一次成孔工艺,利用冲洗液平衡原理处理浅海钻进护简断裂的成孔方法,改进浇灌清孔流程,保证浇灌质量。 相似文献
37.
笔者报告了23例化脓性脊柱炎。本文着重分析对比了X线平片和CT检查结果,通过分析对比,发现CT检查优于X线平片,并有助于对化脓性脊柱炎早期作出诊断。主要影像学表现:早期,软组织肿胀和脓肿形成,骨质呈虫蚀状破坏,随之破坏区周围出现增生硬化。CT还能发现炎块中的气块,晚期骨修复占优势,即骨质增生硬化,骨桥形成,最后可产生骨性融合。 相似文献
38.
高烈度区连续梁桥的减震设计方法研究 总被引:2,自引:1,他引:2
本文以高烈度区的某三跨连续梁桥为例,分别采用基础隔震和消能减震两种措施进行结构的减震分析;针对隔震结构减震效果好但主梁位移过大的特点,提出了在采用铅芯橡胶隔震支座的同时设置粘滞阻尼器的减震方案,其非线性时程分析结果表明,该方案能有效地降低结构的地震反应,可供工程实践参考。 相似文献
39.
Strong near-fault ground motion, usually caused by the fault-rupture and characterized by a pulse-like velocity- wave form, often causes dramatic instantaneous seismic energy (Jadhav and Jangid 2006). Some reinforced concrete (RC) bridge columns, even those built according to ductile design principles, were damaged in the 1999 Chi-Chi earthquake. Thus, it is very important to evaluate the seismic response of a RC bridge column to improve its seismic design and prevent future damage. Nonlinear time history analysis using step-by-step integration is capable of tracing the dynamic response of a structure during the entire vibration period and is able to accommodate the pulsing wave form. However, the accuracy of the numerical results is very sensitive to the modeling of the nonlinear load-deformation relationship of the structural member. FEMA 273 and ATC-40 provide the modeling parameters for structural nonlinear analyses of RC beams and RC columns. They use three parameters to define the plastic rotation angles and a residual strength ratio to describe the nonlinear load- deformation relationship of an RC member. Structural nonlinear analyses are performed based on these parameters. This method provides a convenient way to obtain the nonlinear seismic responses of RC structures. However, the accuracy of the numerical solutions might be further improved. For this purpose, results from a previous study on modeling of the static pushover analyses for RC bridge columns (Sung et al. 2005) is adopted for the nonlinear time history analysis presented herein to evaluate the structural responses excited by a near-fault ground motion. To ensure the reliability of this approach, the numerical results were compared to experimental results. The results confirm that the proposed approach is valid. 相似文献
40.
大跨度斜拉桥变形监测研究 总被引:16,自引:0,他引:16
系统地介绍现代大跨度桥梁变形监测的内容、变形监测的方案与资料分析,结合武汉长江二桥的监测实践,指出利用现代测量仪器和技术,如GPS定位系统、测量机器人等不仅完全可以满足大跨度桥梁管理部门提出的要求,而且还可以提高测量速度,其测量成果也具有很高的精度。 相似文献