基于探地雷达的水泥土探测试验及病害数值模拟

发布时间：2018-06-06 18:54

本文选题：探地雷达 + 水泥土　；参考：《合肥工业大学》2017年硕士论文

【摘要】：探地雷达可以无损、连续的扫描,且具有结果显示直观、探测精度高、速度快等优点,在水利、土木、交通等工程的物探和无损检测中得到广泛应用。但作为水利工程中常见的水泥土防渗体等水泥土构筑物,目前鲜见开展无损检测,基于开挖、取芯等破坏性检测可能造成新的工程结构损坏。分析发现,这实际上是由于在水泥土结构实际探测过程中仍然存在着诸多问题没有得到解决,如水泥掺入比、龄期等水泥土特性对探地雷达探测精度的影响,水泥土工程病害的雷达图像解释依据不确定等。因此,开展基于探地雷达的水泥土探测试验研究和水泥土工程常见病害的数值模拟研究,具有一定的理论和实践参考价值。本文利用探地雷达对室内不同掺入比的水泥土试块进行无损检测,研究电磁波在不同掺入比(8%、12%、16%、20%)、不同龄期(3d、7d、14d、28d、60d、90d)的水泥土试块中波速变化规律,通过波速反演出其介电常数;在此基础上研究分析水泥土抗压强度与介电常数之间的关系,并研究水泥土含水率的变化规律。结果表明:在同一水泥掺入比内,波速随龄期的增加而增加;在同一龄期内,波速随水泥掺入比的增大而减小;相同掺入比,随着龄期的增加,水泥土相对介电常数逐渐降低;相同期龄,随着水泥掺入比的增大,相对介电常数逐渐增大;同一水泥掺入比,相对介电常数与无侧限抗压强度呈负相关关系,同一龄期下,则成正相关关系;水泥土含水率的变化规律与相对介电常数变化规律一致;用于探地雷达探测土壤含水率的经验公式并不适合水泥土含水率的检测,需重新拟合公式。基于时域有限差分法(FDTD),对水泥土工程中空洞、脱空和疏松病害进行数值模拟研究。研究表明:充气空洞反射波的强度最强,充水空洞次之,充泥空洞最弱,介质的反射系数决定反射强度;垂直分辨率不仅与天线的中心频率、介质相对介电常数有关,还与脱空内所含介质有关;疏松的雷达波形散乱,不具备同相轴特征,在雷达剖面上,充气疏松的范围比充水疏松要小。
[Abstract]:Ground penetrating radar (GPR) has been widely used in geophysical prospecting and nondestructive testing in water conservancy, civil engineering and traffic engineering because of its advantages of non-destructive, continuous scanning, visual display, high detection accuracy and high speed. However, as a common cement soil structure in water conservancy projects, nondestructive testing is rarely carried out at present. Destructive testing based on excavation and coring may cause damage to new engineering structures. It is found that this is actually due to the fact that there are still many unsolved problems in the actual detection of cement-soil structure, such as the influence of cement mixing ratio, age and other cement-soil characteristics on the accuracy of GPR detection. The radar image interpretation of cement soil engineering diseases is uncertain. Therefore, the research of cement soil detection test based on ground penetrating radar and the numerical simulation of common diseases in cement soil engineering have certain theoretical and practical reference value. In this paper, using ground penetrating radar (GPR), the nondestructive testing of cement soil samples with different mixing ratios is carried out, and the variation law of wave velocities in cement soil samples with different mixing ratios is studied, and the dielectric constant of the cement soil samples with different mixing ratios is studied, and the wave velocity changes in the cement soil samples of different ages (3 days, 14 days, 28 days or 60 d ~ 90 d), and the dielectric constant of the cement soil samples is obtained by inverse wave velocity. On this basis, the relationship between compressive strength and dielectric constant of cement-soil is analyzed, and the variation law of moisture content of cement-soil is studied. The results show that the wave velocity increases with the increase of the age, decreases with the increase of the cement ratio, decreases with the increase of the age of cement, and decreases with the increase of the age of cement. At the same age, the relative dielectric constant increases with the increase of cement blending ratio, and the relative dielectric constant is negatively correlated with the unconfined compressive strength at the same cement ratio, and is positively correlated at the same age. The rule of change of moisture content of cement soil is consistent with that of relative dielectric constant, and the empirical formula used to detect soil moisture content by ground penetrating radar is not suitable for the detection of soil moisture content of cement soil, and the formula needs to be refitted. Based on FDTD method, numerical simulation of cavities, voids and loose diseases in cement soil engineering is carried out. The results show that the reflected wave intensity of aerated cavity is the strongest, the water filled cavity is the second, the mud filled cavity is the weakest, the reflection coefficient of the medium determines the reflection intensity, and the vertical resolution is not only related to the central frequency of the antenna, but also to the relative dielectric constant of the medium. It is also related to the medium contained in the void, the loose radar waveform is scattered, and it does not have the characteristics of the same phase axis. In the radar section, the range of aeration porosity is smaller than that of water filling.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV221

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