新世界会展中心大直径桩检测及数值模拟分析

【作者】 韩冰；

【导师】 乔登攀； 王述红；

【作者基本信息】 昆明理工大学 ， 岩土工程， 2010， 硕士

【摘要】 随着我国基本建设事业的迅速发展,桩基础在高层建筑、重型厂房、桥梁、港口码头、海上采油平台以及核电站等工程中应用广泛。桩基础朝着大直径高承载力的方向发展,大直径桩的检测也越来越重要。本文依托沈阳新世界会展中心一期试桩检测工程,该桩桩径0.85m、桩长52.0m、长径比为56～62属大直径长桩。由于此前本地区未有类似的工程,施工及检测经验缺乏,需通过试验结果来验证设计,以保证工程质量。本文采用目前最直接、最可靠的检测方法--基桩静载试验法进行承载力测定,得出的Q-s曲线为缓变型,且该工程中桩的长度变化并没有引起桩的Q-s曲线发生太大的波动,表明增加桩长对于承载力的提高不明显,还不利于沉降控制。若要改进设计需综合考虑桩长、桩径,选择合适的长径比。可适当缩短桩长至44m,改变长径比以便发挥端阻作用、降低成本。并针对该地区的地层结构近似地将该地区的砂土地基视为同一介质的地基。通过回归分析得出了Y=A+B×X公式和A=C+D×L；B=C+D×L公式,能有效描述该地区类似土层介质条件下桩身轴力与深度变化关系,对本地区或类似的工程有一定的借鉴作用。针对成桩过程中可能出现断桩、离析等情况的缺陷桩。经过与其他完整性检测方法的对比,选择了适合于本工程桩身的完整性检测的方法—低应变反射波‘法。该法具有快速、经济、可大面积普查等特点。由于现场的检测条件复杂,影响因素较多,难以得到非常标准的完整检测波形,本文采用了通过联系地质情况分析实测波形的方法对其桩身完整性类别作出了判断,综合判别为Ⅰ类桩。因现场试验用桩均为工作用桩,不可以也不可能进行破坏性试验,因而本文运用FLAC 3D(三维快速拉格朗日法)对桩进行了破坏性模拟分析,采用结合地质报告提供的力学参数以模拟结果与桩承载试验结果基本一致为原则,并将模拟结果与实测数据进行比对,对参数不断调整,最终确定了与实际相近的模拟参数。以此进行桩极限承载数值模拟,得到了桩的极限承载力,并提出了后压浆及扩大头的优化设计方案,同时对该方案进行数值模拟,所得结果表明可以缩短桩长、减小钢筋用量、节省了工程费用。并为本地区类似桩基工程的设计和施工提供了一定的参考依据。更多还原

【Abstract】 With the rapid development of China’s Infrastructure,the high-rise buildings, heavy plant, bridges, ports, offshore oil platforms,nuclear power plants and other projects use pile foundation extensively.The pile foundation increaseingly developed into high bearing capacity.so,the detection of large diameter piles foundation engineering has become an important part.This article relies on a test pile detection engineering of Shenyang New World Convention & Exhibition Center. The pile diameter is 0.85m, its length is 52.0m, and length-diameter ratio is between 56 and 62, which belongs to the large diameter long pile. As there is no similar projects in this region, lacking of the experience of Construction and Detection, the design need to be verified by experiments, so that the engineering quality can be assured.At present, the most direct and reliable detection method is foundation pile static load test. According to this test, the Q-s curve is Slow variant, and it did not show any great fluctuation with the length Change of the pile, which reveal that increasing length of the pile can not increase bearing capacity Significantly, and it Is not conducive to settlement control. So if the design need to be improved, the pile length and diameter should be considered comprehensively, and choose a proper length-diameter ratio. In order to exert the end-friction effects and lower cost, the pile length can be properly shorten to 44m with the changing of length-diameter ratio. And in connection with the stratum structure of the region, the sand foundation of the region can be approximately regarded as the Same medium foundation. By regression analysis, the formula are obtain as follows, Y=A+BX and A=C+DL;B=C+DL, it can effectively describe the relationship between axial force of pile shaft and depth variation under conditions of the similar soil medium in the region, which has some reference for the similar projects of this region.In the course of pile-forming, defective piles can be showed as broken or segregation. Compared with other Integrity detection, low-strain reflected wave method is the most suitable method for this project. The method has the following characteristics, such as rapid, economic, and can survey a large area. As the complexity of the field test conditions and many influencing factors, the Pretty standard Full test waveform can be hard to obtained. This article has determined the pile Integrity class through the method of contacting Geological conditions to analysis the measured waveform, which is identified as class I pile.As the Field experimental piles are all the piles for work, it can not be impossible to conduct destructive test. The destructive Simulation analysis of the pile is carried out with FLAC 3D(Fast Langrangian Analysis of Continua 3 Dimensions), and the ultimate bearing capacity of the pile was obtained, proposing the post grouting and enlarged base optimal design. At the same time, Numerical Simulation is conducted for the Program. The result shows that the length of Pile can be shortened,so that the steel consumption and project cost can be decreased,and it can provide a certain frame of reference for the similar design and construction of pile foundation engineering in the region.更多还原