复杂岩土工程介质中全波场传播特性及相关无损检测方法研究

The study on revealing internal structure of medium by varies of detection method has been one of the important and difficult subjects in geotechnical engineering. And the inversion of elastic parameters of medium is an effective way to grasp the internal structure. Full-waveform inversion (FWI) is a challenging data-fitting procedure based on full-wave field modeling to extract quantitative information such as elastic parameters from seismograms. It attempts to match the actual parameters by some iterative approaches by utilizing the amplitude, travel time and phase of measured waveforms comprehensively. The full waveform from seismic data can also be used in time domain inversion, and work out the stratum elastic parameters, such as P-wave velocity, S-wave velocity, and medium density, that is helpful for lithology recognition. For it can only reflect the deteriorations on the surface of the medium using the series of existing nondestructive testing methods in the geotechnical engineering, this study intends to optimize source excitation, settings and array combination of detectors based on its frequency characteristics and operability for its on-site environment, and focuses on the application of full wave field survey techniques on the geotechnical engineering. Testing data of P-wave, S-wave, surface wave, sound waves and rebound instrument can be obtained only once using 3-component detectors, multi-channel receiver and array setting method. The model test and numerical simulation using finite difference method is conducted for a variety of complex geotechnical medium models. The propagation characteristics of full-wave field in the complex geotechnical engineering medium and the corresponding inversion method will be studied. The distribution and elastic parameters for 3-D complex geotechnical engineering medium could be obtained, and then the theoretical method of full-wave field nondestructive testing is expected to be established. According to the obtained S-wave velocity, P-wave velocity, frequency dispersion characteristics of surface wave, sound properties, recorder of rebound method and inversion results of full waveform, the deterioration, peeling, loose of surrounding rock and the formation of cavity within the range of 1-2 m depth should be determined. Finally, a comprehensive evaluation method based on spatial analysis technology could be formed using GIS spatial analysis and GeoDatabase spatial database technology.

采用各种探测手段揭示介质内部的构造一直是当今工程界的重要课题和难题。全波形正演、反演计算方法能够综合利用波场的振幅、走时及相位信息，获得介质的弹性参数。针对现有的各种无损检测方法只能反映介质表面劣化情况的缺陷，本研究拟从频率特性和现场环境的可操作性等方面优化震源激发方式、检波器设置方式以及阵列组合等，重点解决全波场检测技术在岩土工程结构缺陷快速检测中的应用。采用3分量多通道阵列方式，一次检测获得纵波、横波、面波以及声波检测数据，通过建立各种复杂岩土工程介质模型，进行模型试验及有限差分数值计算，研究复杂介质中全波场传播特性及构造反演方法，解决全波形反演中存在的结果的不唯一性、迭代矩阵确定、反演运算量大等问题，获得三维复杂介质的构造分布及弹性参数，建立全波场无损检测理论方法。最后运用空间数据库技术，形成基于空间分析技术的综合评价方法，对科学、规范的进行岩土工程安全性评价具有重大意义。

弹性波全波场无损检测技术是以电子技术、计算技术和图像处理技术的最新发展成果为基础研发的全新检测手法，包括了全波场采集和全波场处理等各个方面。全波场技术是一种全方位、全频带、全分量、高保真的矢量检测技术。采用大量的3分量传感器把介质表面的波动场的大小和方向都记录下来，通过复杂的数学分析，由波动场数据构建介质内部结构的3维图像和物性分布。与常规弹性波检测技术相比，全波场检测勘察技术具有以下特点：（1）能够准确记录到地面的多分量震动特征，得到P波、S波、瑞利面波等速度场信息，这其中也包括了各种背景噪音。（2）全频带记录宽度，特别是对低频信号的保护。（3）成像解释信息较为精确且丰富。.针对基于弹性波场的岩土工程结构无损检测方法，解决多层层间缺陷问题的全波场传播特性及参数反演方法。建立全波场岩土工程结构无损检测理论方法。开发了科学、快速、经济、规范的全波场无损检测系统及方法。针对我国高速铁路无砟轨道中缺陷病害的无损检测问题，分别在两个等比例的实际模型上，开展弹性波全波形反演方法对预设缺陷的检测试验。鉴于现有的缺陷和损坏较多地存在于轨道基床和CA砂浆这两个相对较为薄弱的结构层中，第一个检测试验在基床层内预设了饱和土及泡沫板两种缺陷材料，根据支承板表面采集到的观测数据，反演计算所揭示的检测区域剪切波速与支承板下预设的缺陷材料吻合较好，缺陷区域位置也基本符合预设情况。第二个检测试验则拓展到完整的CRTSⅡ型标准高速铁路结构模型中。采用地震参考道反褶积运算消除震源波形对反演计算的影响。最终计算结果表明，弹性波全波形反演方法能对CA砂浆层脱空病害以及基床层上部的材料缺陷有较明显的定量化揭示，反演计算所揭示的缺陷区域位置与预设基本符合，但由于计算误差的影响，区域范围有所放大。