低应变反射波法检测嵌岩桩质量影响因素的探讨

发布时间：2018-02-08 12:45

本文关键词： 嵌岩桩混凝土抗压强度低应变反射波法 MIDAS/GTS NX　出处：《南昌大学》2016年硕士论文　论文类型：学位论文

【摘要】：在基岩埋深较浅的地区,通常采用嵌岩桩作为高层建筑、桥梁的基础工程,因此其嵌岩效果很引人关注。重要工程的建设中通常是百分之百的基桩进行低应变反射波法的检测,结合少量钻芯法分析嵌岩桩的入岩深度和桩底沉渣情况,为工程质量总体把关。问题是当前钻芯法抽取的少量嵌岩桩比较随意、盲目,而影响低应变反射波法的因素比较多,尤其是嵌岩桩的特征增加了检测复杂性,导致基桩嵌岩效果的检测评价并不如意,需要进一步研究探讨检测机理和方法。本文通过南昌某工程嵌岩桩质量检测活动,经过取芯桩的混凝土芯样抗压试验,发现不少基桩,同一根桩不同深度部位混凝土抗压强度差异较大。然而以往在实际混凝土灌注桩基检测分析中,对于比较完整的基桩,通常均认为沿整个桩身为均匀材质。把检测信息的变化就认为是桩身存在一定的质量问题,产生了一定的误判。因此,为了解桩身混凝土抗压强度对低应变反射应力波的影响,特别选取其中5根取芯桩,将桩身混凝土逐米取一组芯样进行混凝土抗压试验,得到这5根桩混凝土抗压强度的变化情况,并与低应变反射应力波方法检测结果进行比较分析。结果表明,由于该工程桩基施工完成后停工将近一年,桩身混凝土强度基本上达到极值,沿桩身的混凝土强度有些大大超过28天正常混凝土设计强度,出现了明显的差异性、随机性的情况。而随着桩身混凝土强度的剧烈变化,低应变反射波的反射信号杂波越多,桩底反射信号越不明显。为了进一步了解桩身混凝土抗压强度等相关参数对低应变反射应力波曲线变化的影响,运用有限元分析程序MIDAS/GTS NX建立模拟桩-土振动模型。探讨了完整桩在激振力、脉冲宽度、桩顶信号接收点位置、桩长对应力反射波时间-速度曲线的影响;研究了桩身缺陷在扩径与缩径缺陷长度、半径大小、缺陷位置因素下,应力波时间-速度曲线变化规律;探讨桩侧土与桩底土弹性模量、容重、泊松比、粘聚力和摩擦角等因素影响下,应力波的变化规律;分析了桩长、桩径、混凝土标号、桩底沉渣厚度参数变化对应力反射波时间-速度曲线的影响。得到一些有益结论,加深了各个因素对于低应变反射应力波信号影响性质和影响程度的理解、认识,论证了桩身混凝土变化对低应变反射波曲线的复杂影响。这对于今后指导分析工程桩基检测与分析评判工作具有比较大的作用。
[Abstract]:In areas with shallow bedrock depth, rock-socketed piles are usually used as foundation works for high-rise buildings and bridges, so the effect of rock-socketed is very interesting. In the construction of important projects, 100% of foundation piles are usually used to detect the low strain reflected wave method. Combined with a small amount of core drilling method, the depth of rock socketed pile and the sediment situation of pile bottom are analyzed. The problem is that a small number of rock-socketed piles extracted by drilling core method are relatively random and blind, but there are many factors that affect the low strain reflection wave method. Especially, the characteristics of rock-socketed pile increase the complexity of detection, which leads to the unsatisfactory testing and evaluation of the rock-socketed effect of the foundation pile, so it is necessary to further study the testing mechanism and method. In this paper, the quality detection of rock-socketed pile in a project in Nanchang is studied. Through the compression test of concrete core sample of cored pile, it is found that there are many foundation piles, and the compressive strength of concrete at different depth of the same pile is quite different. However, in the past, in the testing and analysis of actual concrete cast-in-place pile foundation, for the relatively complete foundation pile, It is generally considered that the pile is a homogeneous material along the whole pile. The change of testing information is regarded as the existence of a certain quality problem in the pile body and a certain misjudgment. Therefore, in order to understand the influence of the compressive strength of the pile body on the low strain reflected stress wave, In particular, five coring piles are selected, and a group of core samples are taken from the pile body concrete to test the compressive strength of the concrete, and the change of compressive strength of the pile concrete is obtained. The results are compared with the results of low strain reflection stress wave method. The results show that the strength of concrete of pile body basically reaches the extreme value because the construction of pile foundation is stopped for nearly one year. Some of the concrete strength along the pile body is much higher than the normal concrete design strength for 28 days, and there are obvious differences and randomness. However, with the violent change of the concrete strength of the pile body, the more clutter of the reflected signal of the low strain reflection wave, The less obvious the reflected signal of pile bottom is, in order to further understand the influence of some related parameters, such as compressive strength of pile body concrete, on the change of low strain reflected stress wave curve, The finite element analysis program MIDAS/GTS NX is used to establish the model of pile-soil vibration. The effects of the excitation force, pulse width, the position of the signal reception point on the top of the pile and the pile length on the time-velocity curve of the stress reflection wave are discussed. The variation law of time-velocity curve of stress wave is studied under the factors of the length, radius and position of the defect, the elastic modulus, bulk density and Poisson's ratio of pile side soil and pile bottom soil are discussed. Under the influence of cohesive force and friction angle, the variation law of stress wave is analyzed, and the influence of pile length, pile diameter, concrete label and sediment thickness on the time-velocity curve of stress reflection wave is analyzed. It has deepened the understanding and understanding of the influence of various factors on the properties and the degree of influence of the low strain reflected stress wave signal. The complex influence of pile concrete variation on the low strain reflection wave curve is demonstrated, which has a great effect on guiding the detection and analysis of pile foundation in the future.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU473.16

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