岩土随机介质中的超声波场及其相控阵检测关键技术

As a typical concealed engineering, the Non-Destructive Testing(NDT) of underground structures has taken widely attentions. With the depth increase, the steel quantity and the thickness of the underground structures have also increased. Especially in the deep underground structure, the widely used multi-rebar reinforced concrete and steel-concrete structure in the deep underground engineering have limited the application of the Geophysical methods used in the the common underground engineering. It was needed to develop a new NDT method via ultrasonic wave. Ultrasonic Phased Array(UPA) has the characteristics of high precision, high detection rate, high efficiency, and can realize dynamic focusing. It was widely applied in medical diagnosis, metal structure detection et al. However, because of the significant stochastic vibration of the geotechnical media, frequency dispersion would be inevitable when the high frequency ultrasonic wave propogated in the stochastic geotechnical media, and the Signal to Noise Ratio (SNR) would be decreased largely. So,the conventional UPA device could not be applied directly in the NDT of geotechnical engineering. In this project,through the acoustic parameters testing of geotechnical media, geotechnical stochastic media model would be established ; Based on the stochastic model, through numerical simulation and exprimental test, the the ultrasonic wave field in geotechnical random medium would be studied ;Then,UPA with suitble lower frequency signalul would be developed,and the model experiment test and field exploration would be carried out to master the characteristics of typical defects in underground structure.In this project, geophysical methods would be developed to solve the major technical problems of deep underground engineering, and the interdisciplinarity and underground engineering characteristics are noticeable.

作为典型的隐蔽工程，地下结构健康检测广受重视。随深度增加，地下结构的用钢量增加、厚度增大。尤其在深部地下工程中，普遍采用多排钢筋或钢板混凝土等结构形式，浅部地下工程检测中中常用的物探方法不再适用。超声相控阵具有高精度、高检出率、高效率的特点，可实现动态聚焦，在医学诊断、金属结构检测等领域应用广泛。然而，岩土介质具有显著的随机性，高频率的超声波将在其中出现频散导致信噪比降低，常规的超声相控阵设备在岩土工程检测中并不适用。本项目拟从岩土介质的声学参数测试出发，建立岩土随机介质模型；通过数值模拟和模型试验，获得岩土随机介质中超声波场的传播规律，确定适与地下工程检测的超声波频带；进而，研发相对低频的、适于地下工程检测的超声相控阵设备，并通过模型试验和现场实测，获得地下结构中典型缺陷的相控阵图像特征。本项目采用物探手段解决深部地下工程的重大技术难题，有典型的学科交叉特点和深部地下特色。

深部地下结构作为典型的隐蔽工程，其无损检测广受重视。深部地下结构的无损检测，因其用钢量大、厚度大，在浅部地下结构检测中采用的探地雷达、冲击回波法等的应用效果不佳。究其原因，在于信噪比低、探测距离不敷使用。本项目提出从岩土介质赋存地质环境与内部结构特征出发，研究岩土随机介质的超声波场，进而掌握适用于岩土随机介质超声相控阵检测的关键技术。首先，设计了真三轴加载的超声波检测装置，测得了深部岩土和混凝土试样的波速，获得了混凝土强度、应力与声波速度的关系，并与数值模拟结果进行对比分析。其次，根据混凝土的二维图像，采用FFT变换生成一个具有较高计算效率的三维初始灰度随机分布模型，再利用随机优化算法对随机扰动进行改进，以加速模拟退火算法的收敛，提出了一种新的描述两相随机介质特性的统计函数——长方体函数，实现了三维混凝土结构的随机建模重建；对于结构损伤，采用随机裂隙介质模型，根据裂隙的统计信息建立形状、大小、倾向、倾角及分布位置的概率分布特征，采用等效介质理论计算其等效模量，建立了裂隙参数与时频相关的衰减剖面的关系。在此基础上，开展岩土随机介质超声波场的数值模拟，获得了超声信号的衰减响应和波场特征，进而根据相控阵的延迟定律及多源激励技术，研发了集信号激发、接收为一体的超声相控阵检测系统，该系统为16通道，延时精度1μs，激励电压500V，频率范围1—50KHz的声波信号可以解决混凝土结构和岩土体内部缺陷的检测问题。本项目在岩土随机介质建模、超声波场分析方面取得的科学进展，具有创新性，为复杂介质中的弹性波场数值模拟研究提供了可靠的模型基础和实现方法。本课题在装备研发方面，解决了（超）声信号频段选择、传感器阵列耦合一致、超声阵列精准调距、系统延时要求、震源激励方式等关键技术难题，获得了具有自主知识产权的技术与装备，上述岩土随机介质建模方法、超声波场模拟方法和自主装备在未来的深部地下结构无损检测中具有广泛的应用前景。