隧道出口明挖段深基坑施工过程中的变形及稳定性研究

发布时间：2018-09-18 20:34

【摘要】：就基坑工程在开挖过程中的内力和变形规律,岩土工作者已做了大量的研究,但对于狭长型基坑在开挖过程中基坑受力、变形机理的实测和分析却较少。随着我国大规模的进行城市轨道建设,这类型基坑会大量遇到,对此类基坑在开挖过程中的受力和变形机理进行研究探讨,可以为以后类似工程的设计和施工积累经验。在阅读大量国内外相关文献,总结相关研究成果的基础上。本文以哈尔滨到牡丹江客运专线(哈牡客专)爱民隧道出口明挖段狭长型深基坑在开挖过程中的现场监测为依托,结合理论分析及三维数值模拟分析,指导现场施工、反馈设计的同时对本地区狭长基坑在开挖过程中围护结构的受力、变形以及开挖对周边环境的影响进行了初步探讨。最后,通过三维数值模拟分析的方法对围护结构参数进行了多方位优化,为工程后续施工以及本地区类似基坑工程设计、施工提供参考。本文主要内容及相关结论如下:(1)通过现场监测可知,基坑施工全过程中,各监测项目的量均未达到报警值,围护结构正常工作。基坑从开挖暴露到底板施做完毕全过程中,桩身水平位移最大值达到13.72mm,位于撑间桩上距桩顶往下8.0m左右处,位置随着最大值增加不断下移,刚开挖到底时最大值在距桩顶7.0m左右处;桩身弯矩最大值也发生在撑间桩上,最大值达到了464.0kN.m,与桩身正截面抗弯承载力1410kN.m相距甚远,究其原因,是由于现场实测得到的桩顶和桩底均发生了一定量的水平位移,这样势必会对围护桩的内力产生一定的释放作用;现场实测得到的横撑和冠梁位移及受力均处于较小状态。(2)对比现场实测、三维有限元分析及规范法得到的桩身水平位移,规范法得到的值最大,最大值达到了16.78mm,最大值发生位置与三维有限元分析得到的最大值位置一致,发生在距桩顶7.5m左右处,现场实测得到的最大值位置略微向下,位于距桩顶8.0m左右处;对桩身弯矩而言,三维有限元分析下的最大值为883.1kN.m,规范法计算的最大值为966.5kN.m,现场实测结果却小很多,最大值只有464.0kN.m,由内里释放引起;冠梁的内力及变形三种方法得到的结果大小与趋势均较接近。(3)为了综合评价基坑的稳定性,通过经验公式和三维有限元分析对地表沉降和坑底隆起进行估算。经验公式得到的地表沉降最大值为10.7mm,发生在距桩顶6.9m处;三维有限元分析得到的地表最大沉降为11.2mm,距桩顶6.5m处;经验公式得到的坑底隆起最大值为10.2mm,三维有限元分析得到的坑底隆起最大值为12.1mm,发生在距离围护结构约1.0m处。(4)各优化方案中,改变锚固段长度对围护结构的受力及变形影响均最小;改变桩径对围护桩及横撑的影响最为剧烈,当桩径从1.0m减小到0.7m时,水平位移最大值达到28.0mm,与30mm的报警值已非常接近,桩身弯矩已达到了桩身正截面弯矩承载力的85.4%,此时横撑弯矩相较原模型增大了139%,已经超过了横撑正截面抗弯承载力815kN.m;冠梁弯矩却是对桩间距的改变最为敏感,但是在整个优化过程中,冠梁弯矩均处于较小状态。最后提出一种适用于按照现场施工工序施工的围护结构设计方案,此方案在保证施工安全的前提下,经济合理。
[Abstract]:Geotechnical workers have done a lot of research on the internal force and deformation law of foundation pit engineering in the excavation process, but there are few measurement and Analysis on the deformation mechanism of the narrow and long foundation pit in the excavation process. On the basis of reading a large number of relevant literatures at home and abroad and summarizing the relevant research results, this paper takes Harbin-Mudanjiang Passenger Dedicated Line (Harbin-Mudanjiang Passenger Dedicated Line) Aimin tunnel exit open-cut section of the narrow deep foundation pit excavation in the excavation. Based on the field monitoring in the process of excavation, combined with theoretical analysis and three-dimensional numerical simulation analysis, the field construction is guided and the feedback design is carried out. At the same time, the force, deformation of the retaining structure and the influence of excavation on the surrounding environment in the process of excavation are preliminarily discussed. The main contents and related conclusions are as follows: (1) Through on-site monitoring, it is known that during the whole process of foundation pit construction, the amount of monitoring items has not reached the alarm value, and the retaining structure works normally. The maximum horizontal displacement of pile body reaches 13.72 m m in the whole process of exposed floor construction, which is located at the position of 8.0 m downward from the top of pile between bracing piles. With the increase of the maximum position, the maximum value is about 7.0 m from the top of pile when excavated. The maximum bending moment of pile body also occurs on the pile between bracing piles, the maximum value is 464.0 kN.m, and the pile top. The bending bearing capacity of the normal section is far from 1410kN.m. The reason is that a certain amount of horizontal displacement occurs at the top and bottom of the pile, which is bound to release the internal force of the retaining pile. The maximum horizontal displacement obtained by the code method is 16.78 mm. The location of the maximum displacement is consistent with that obtained by the three-dimensional finite element analysis. It occurs about 7.5 meters from the pile top. The maximum displacement measured by the field is slightly downward and located 8.0 meters to the left of the pile top. For the pile bending moment, the maximum value of the three-dimensional finite element analysis is 883.1 kN.m, the maximum value of the code method is 966.5 kN.m, but the field measurement results are much smaller, the maximum value is only 464.0 kN.m, which is caused by internal release; the internal force and deformation of the crown and beam are close to the trend of the three methods. (3) In order to evaluate the foundation comprehensively. The stability of the pit is estimated by empirical formula and three-dimensional finite element analysis. The maximum ground settlement is 10.7 mm from the top of the pile and 6.9 m from the top of the pile. 10.2 mm, the maximum value of pit bottom uplift obtained by three-dimensional finite element analysis is 12.1 mm, occurring about 1.0 m away from the retaining structure. (4) In all optimization schemes, changing the length of anchorage section has the least influence on the stress and deformation of the retaining structure; changing the diameter of the pile has the most severe influence on the retaining pile and the transverse brace, when the diameter of the pile decreases from 1.0 m to 0.7 m, the horizontal displacement is the smallest. The maximum value is 28.0m m, which is very close to the warning value of 30m M. The bending moment of pile body has reached 85.4% of the bearing capacity of normal section moment of pile body. At this time, the bending moment of transverse bracing has increased by 139% compared with the original model, and has exceeded the bending capacity of normal section of transverse bracing by 815kN.m. Finally, a design scheme of envelope structure suitable for construction according to site construction procedure is put forward, which is economical and reasonable on the premise of ensuring construction safety.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U455

【参考文献】