【作者】 宋华；

【导师】 王立忠；

【作者基本信息】 浙江大学 ， 岩土工程， 2010， 硕士

【摘要】 探地雷达作为一种无损、高效的工程探测技术,随着近年来经济社会的迅猛发展,已经被广泛应用到岩土工程当中。抛石海堤在海岸堤坝工程中十分常见,而对存在淤泥的地质进行填筑时常使用爆破挤淤法对基底进行地基处理。由于爆破法的效果难以准确控制,使得地基可能存在未排出淤泥层,对堤坝的稳定性产生很大影响。本文针对探地雷达在确定海堤抛石底界的应用进行基础研究,具有重要的工程实际意义。本文首先对探地雷达的原理和主要的工程应用进行了总结,并对探地雷达技术中的探测方法和各参数进行了分析和讨论。采用TDR法对海堤工程中常见的介质进行了电性质测定,针对盐水浸没对碎石介电常数的影响,用探地雷达法测定了各浸没深度的介电常数,并总结出其变化规律和公式。制作海堤模型进行探地雷达海堤探测试验,并用FDTD法进行GPR二维正演模拟,把正演模拟结果与实测结果进行对比验证。分析着重关注了抛石底界的形态和埋深：从实测图像中识别碎石层底界位置,通过计算双程走时差,结合电磁波在该介质中的波速来得到埋深。分别用平均介电常数法和分层计算法对抛石底界进行了计算,总结和比较了两种方法的适用条件,对误差的产生原因进行了分析。试验结果表明：海水对介质电性质的影响很大,介电常数和电导率随含水量的增加而增加,大电导率使介质的复介电常数增大,并使电磁波衰减明显。在海水浸没的条件下,界面形态变平缓,界面反射减弱,探测误差增大。更多还原

【Abstract】 In recent years, ground penetrating radar is commonly used in geotechnical engineering as a non-destructive detection and effective method. Riprap embankment is one of general coastal projects, and explosive compaction is used in foundation treatment of soft soils. Because of uncontrollability of explosive results, residual mud zone in embankment bottom would have negative impacts to stability of riprap embankment. Therefore, investigation of riprap bottom boundary detection with GPR in coastal riprap embankment is an important issue, which is just the object of this thesis.Based on the summary of related work, the parameters and detection methods are discussed. TDR is used in measurement of electrical properties of clay, seawater, gravel. GPR is chosen to measure the permittivity of gravel with saltwater immersion, and permittivity formulas are gotten in different saltwater depths. Furthermore, model experiments are conducted to investigate the influence of seawater on the signal and image of GPR, especially to figure out the image variation of riprap bottom boundary. Then, the measured results are compared with that obtained by numerical FDTD analysis for verification. The back-analysis emphasizes the shape image of riprap bottom boundary under the effects of seawater intrusion. Riprap bottom boundary is calculated respectively through average permittivity method and layered calculation. After comparing the results of both, cause of accuracy error and applicable condition are investigated.The experiment results indicate that seawater has great influence on dialectical properties of materials. GPR is effective to identify the riprap bottom boundary of coastal embankment without seawater. When it is submerged by seawater, the electrical properties of mediums changed significantly, moreover, measurement error is a little bit bigger and the interface image appears fuzzy.更多还原