【作者】 刘雪明；

【导师】 凡友华； 耿光旭；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2008， 硕士

【摘要】 瞬态瑞雷波技术与传统方法相比具有测试技术简单易行、无需钻孔、浅层分辨率高以及高效经济等优点,已经被广泛地应用于地基检测中,但由于缺少大量理论指导,特别是数值模拟方面的研究,其应用受到限制。本文利用有限元软件LS-DYNA对瑞雷波地基检测过程进行了数值模拟,研究了地基检测中震源和瑞雷波“之”字形频散曲线问题,得出以下结论:(1)通过对半空间单层土体数值模拟提取频散曲线的误差的研究分析,说明用有限元方法模拟瑞雷波地基检测过程是可行的。在此基础上,通过对不同震源参数情况下得到频散曲线误差分析发现,加载面越大,频散曲线误差越大;荷载作用时间过大或过小,频散曲线出现弯曲和不规则;荷载大小对频散曲线形态几乎没有影响。这就要求在实际工程中应选择较小的加载面,荷载作用时间适中的震源。(2)通过对四种典型地层(递增型地层、含软弱下伏层地层、含软弱夹层地层、含硬夹层地层)的27个模型瑞雷波“之”字形频散曲线特征的研究发现:对于递增型地层,频散曲线不会出现“之”字形,而且很难通过拐点判断分层位置;而对于其它三种非递增型地层,频散曲线则会出现两种类型的“之”字形,其中含软弱夹层地层,“之”字形的位置和尺寸与软夹层的位置和层厚有较好的对应关系。本文还将数值模拟计算结果与实测结果以及解析解进行了比较,进一步验证了数值方法研究瑞雷波地基检测过程的可行性及“之”字形频散曲线的形成原因。(3)当含软夹层地层有空洞时,频散曲线“之”字形变大,而且频散曲线与无空洞时相比,高频部分出现缺失。而且当空洞位于软夹层,震源下以及近道检波器附近时,对“之”字形频散曲线的形态影响最大。本文的研究为工程实际中震源参数的选取提供可靠依据,也为在实际工程中利用瑞雷波频散曲线的形状判定地层类型和软弱夹层位置提供了重要参考,而在空洞探测方面也提供一定依据。更多还原

【Abstract】 Transient Rayleigh technology has the following advantages over traditional method: easy and feasible testing technique, no need to drill, high resolution in shallow stratums and high efficiency and low cost. It is widely used in stratum exploration, but its application is limited because of no many theory guides; especially numerical simulation research. This article uses the finite elements software LS-DYNA to simulate the processing of Rayleigh wave stratum exploration, and study source and Rayleigh wave zigzag dispersion curve. Then we obtain the following conclusions:(1)Through analysis about errors of extracting dispersion curve simulate from half space single stratum, we know it is feasible to use the finite element method to simulate the processing of Rayleigh wave stratum exploration. On that basis, through analisis about errors of extracting dispersion curve in the case of different source parameters, we discover: average errors of dispersion curve become lager with augment of loading area; dispersion curves appear bend and abnormity, when loading time is too long or too short; but load values hardly act any effect on the shape of dispersion curves. So we should use sorurce with small loading area and moderate loading time in actual engineering.(2)Through study about Rayleigh wave zigzag dispersion curve of 27 models of four typical stratums (stratum of Rayleigh wave velocity would increase with wavelength, the under-layer is soft, weak interlayer, hard interlayer), We know that dispersion curves of the stratum of Rayleigh wave velocity would increase with wavelength can’t appear zigzag, but we can not juge layered position through inflections. However, Rayleigh wave dispersion curves of other stratums will appear two different types zigzag. For the sratums containing weak interlayer, zigzag position and size of stratums matches better with position and layer thickness of weak interlayer. This article also compares numerical simulation results with analytical solution, and further verifies feasibility of reasearching the processing of Rayleigh wave stratum exploration; also explains the genesis of zigzag dispersion curve.(3)When stratums containing weak interlayer have a hole, zigzag dispersion curve becomes larger. And comparing with stratums containing no hole, high frequency of dispersion curve appears missing points. When holes locate in weak interlayer, under source and close to nearby geophones, the shape of zigzag dispersion curve varies largest.The results of the article offer reliable basis for the choice of source parameters in actual engineering, supply important reference for using dispersion curve shape to determine stratum types and position of weak interlayer in actual engineering, and also provide certain foundation for hole exploration.更多还原