【作者】 王永翔；

【导师】 邓荣贵；

【作者基本信息】 西南交通大学 ， 岩土工程， 2010， 硕士

【摘要】 圆形基坑周围土体具有拱效应,作用于支护结构的土压力与直边基坑直边中部的土压力相比将会大大降低；如果采用弧形或圆形支护结构,在土压力作用下支护结构内力以周向压应力为主,几乎不存在弯曲拉应力,这样能充分发挥了混凝土抗压性能高特性,因此其应用越来越广泛。本文对德阳市二重厂厂房内淬火炉装置圆形基坑的空间效应、支护方案及支护结构内力等进行了较为系统的研究。主要研究内容及获得结果如下：(1)对圆形基坑可选用的支护结构型式进行了总结与论证分析,结果表明采用“品”字形密排桩墙+内支撑+桩间混凝土充填的半逆做法,同时用旋喷桩作为止水的支护结构方案,是该基坑支护技术可靠、经济合理和实施性强的最佳方案。(2)圆形支护结构与通常的线状支护结构比较,具有显著的空间结构效应,在同样的土压力作用下支护结构内力以压应力为主,针对土压力随深度增加,若按照平面问题分析其误差较大。本文提出一种厚壁圆筒受等效的线性分布土压力及内支撑力的空间结构力学模型,应用弹性力学得出应力及位移解析解。结果表明,这种计算方法得到的支护结构内力、变形较小,更接近于实测值。(3)建立有限差分模型,对采用的排桩墙+内支撑圆形支护结构进行三维数值模拟,分析支护结构及周边环境应力场及变形状态。结果显示支护结构变形小,围护桩最大位移约22mm；基坑开挖对周围环境的影响也小,基坑开挖引起的最大沉降约7mm,说明这种支护结构合理可靠。(4)根据工程实际情况,制定基坑施工监测方案,对基坑开挖过程中土压力值、支护结构内力、围护桩侧向位移等内容实施动态监测,及时掌握基坑支护结构安全情况及周边环境。对实测数据的分析表明,基坑开挖过程中土压力值变化连续,且变化值较小,说明基坑开挖对周围环境的影响处于可控范围内。(5)将理论计算、数值模拟及实测结果进行对比分析。三者土压力分析结果表明,土压力均呈现“中间大,两头小”的分布规律,且在18m-23m之间达到最大值。数值分析得到的土压力值最大,理论计算值次之,实测值最小,造成这种差异的原因为理论计算与数值分析均进行了一定的简化,数据的提取位置也存在误差；三者分析方法土压力最大值均控制在0.9MPa以内,说明三者又存在一定的统一性,说明本支护结构是合理、可靠的,可为类似工程提供一定的参考。更多还原

【Abstract】 Earth pressure acting on the retaining structure is reduced greatly comparing to the middle position of straight side, because there is soil arching effect around the circular foundation pit; main stress of the retaining structure is pressure under circular retaining structure, and there is nearly no tensible pressure so the high pressure property of the concrete can work fully, as a result, more and more circular retaining structure appear. In this paper, take the quenching furnace foundation engineering of the China Secondary Heavy Machinery Group as an example, study the space effect, the supporting scheme and the internal force of the retaining structure and so an. Main research contents and results are as follows:(1) Argue on various retaining structures which can be applied to circular foundation pit, it shows that the retaining structure of piles in row+internal bracing+concrete padding between piles+sealing works of Jet Grouting Piles is dependable, economical, operable and reasonable, and it is the best retaining structure to this foundation pit.(2) Comparing with the linear retaining structure, space effect is prominent in the circular retaining structure, and the main internal force of the retaining structure is pressure under the same earth pressure; because earth pressure increase with depth rising, the inaccuracy is larger depending on plane problem. In this paper, propose a mechanics model that thick-walled cylinder bearing linear soil pressure and inner supporting, and obtain stress and displacement solution. The result shows that the internal force and the deformation of supporting structure are both smaller and closer to the measured value.(3) Build a finite-difference model to simulate the foundation pit excavating, and study the stress field changes and deformation of the retaining structure and the environment. The result shows that deformation of the retaining structure is smaller, and the largest deformation is only about 22mm; influence causing by foundation pit excavation is also smaller, and the largest settlement is only 7mm, it shows that this retaining structure is reasonable and dependable.(4) According to actual situation, establish a monitoring scheme for foundation pit excavation to monitor earth pressure, internal force of retaining structure and so on, so the retaining structure safety and surrounding environment changes can be known in time. The monitoring data analysis shows the value of earth pressure change continuous and changes are smaller, so it is indicated that the influence of foundation pit excavation is controlled in a rational range.(5) Compare the theoretical, numerical simulation and monitoring results. The results show that earth pressure present distribution of "middle larger, sides smaller", and the largest earth pressure appear at depth range that 18m to 23m. The earth pressure value of numerical simulation is the largest, followed by theoretical value and the monitoring value is the least, the reason leading to this difference is that theoretical calculation and the numerical analysis are both simplified, meanwhile, data position are different a little. The results in three methods are controlled in 0.9MPa so that the results are consistent in some degree, it shows that this retaining structure is reasonable and reliable, and it can prove some experience to the similar project.更多还原