土质路基含水性与介电性的关系研究

发布时间：2018-04-16 16:14

本文选题：土质路基 + 介电常数　；参考：《湖南科技大学》2014年硕士论文

【摘要】：土质路基含水量是整个路基路面强度和稳定性的重要影响因素，通常采用钻孔取样等方法进行测试，结果准确、可靠，但成本高、效率低、代表性差，对既有道路、特别是营运中的路段而言，这种破损检测方法实际上很难实现。探地雷达法是以电磁波传播理论为基础，以介质电性（导电性和介电性）差异为前提的探测技术，而介质含水量差异越大其电性差异就越明显，因此，可以用该方法来研究地下介质的含水性。本文基于探地雷达探测理论和方法，研究路基土含水量与介电常数的关系，试图建立二者之间的经验公式，为运用探地雷达方法研究路基含水性提供理论和方法支持。本文采用基于时域有限差分法的GPRMax2D软件，建立了不同含水量、不同介电常数及典型病害类型的单层、多层介质模型，模拟分析了电磁波的相位、振幅、双程走时等响应特征和规律，即：路基土含水量增加会使介电常数和电导率变大，使电磁波的传播速度变小，表现为同一深度的雷达回波的双程走时增大；当电磁波由介电常数小的介质入射到介电常数大的介质时，反射系数为负值，其反射波的相位与激发电磁波的相位相反，反之亦然；当上下界面的介电常数相差较大时，反射系数的绝对值也较大，会引起电磁波的强反射；电导率越大对电磁波的吸收越明显，使其振幅变小；但电导率的差异不会影响雷达电磁波的传播速度。为了采用探地雷达测定路基土的含水量，在数值模拟的基础上设计了物理模型。通过改变模型介质的含水量，，获得电磁波在不同含水量介质中的传播速度，再根据低损耗介质中电磁波速度与介电常数的关系求得介电常数，分析、统计、拟合出土体含水量与介电常数的数学关系式。与常用的Topp、Alharathi等经验公式模型进行了对比分析，其结果具有一致的趋向性。结合实际路段雷达的探测结果，分析了路基的含水性及其对路基路面强度和稳定性的影响。研究表明，不同含水量的土质路基的雷达响应特征不一样，含水量越大，反射信号双程走时越长，幅度和频率越低。通过多种模型的模拟分析，可加深对雷达反射剖面的认识，有利于提高解释精度和准确性。
[Abstract]:The moisture content of soil subgrade is an important factor affecting the strength and stability of the whole roadbed and pavement. The results are accurate and reliable, but the results are accurate and reliable, but the cost is high, the efficiency is low, and the representativeness is poor.Especially in operation, the damage detection method is very difficult to achieve.The GPR method is based on the theory of electromagnetic wave propagation and is based on the difference of dielectric conductivity (conductivity and dielectric property). The greater the difference of water content in the medium, the more obvious the difference in electrical property.This method can be used to study the water content of underground media.Based on the theory and method of ground penetrating radar, this paper studies the relationship between the water content of subgrade soil and dielectric constant, and tries to establish the empirical formula between them, which provides theoretical and methodological support for the application of ground penetrating radar method in the study of subgrade water content.In this paper, using GPRMax2D software based on finite difference time-domain method, a single-layer and multi-layer dielectric model with different water content, different dielectric constant and typical disease type is established, and the phase and amplitude of electromagnetic wave are simulated and analyzed.The characteristics and rules of two-pass travel time are as follows: the increase of water content in subgrade soil will make the dielectric constant and conductivity increase, and the propagation speed of electromagnetic wave will become smaller, which shows that the two-pass travel time of radar echo of the same depth increases;When electromagnetic wave is incident from medium with small dielectric constant to medium with large dielectric constant, the reflection coefficient is negative, the phase of reflected wave is opposite to that of excited electromagnetic wave, and vice versa.The larger the absolute value of the reflection coefficient is, the stronger the electromagnetic wave will be; the greater the conductivity is, the more obvious the absorption of the electromagnetic wave is and the smaller the amplitude is, but the difference of the conductivity will not affect the speed of the radar electromagnetic wave propagation.In order to measure the moisture content of subgrade soil by GPR, a physical model is designed on the basis of numerical simulation.By changing the water content of the model medium, the propagation velocity of electromagnetic wave in different water content medium is obtained. According to the relationship between electromagnetic wave velocity and dielectric constant in low loss medium, the dielectric constant is obtained.The mathematical relationship between soil moisture content and dielectric constant is obtained.The results are compared with the usual empirical formula models such as Toppia Alharathi and so on. The results are consistent with each other.Combined with the radar detection results of the actual section, the water content of the roadbed and its influence on the strength and stability of the roadbed and pavement are analyzed.The results show that the radar response characteristics of soil subgrade with different water content are different. The larger the water content, the longer the two-way walk time and the lower the amplitude and frequency of the reflected signal.Through the simulation and analysis of various models, the understanding of radar reflection profile can be deepened, and the accuracy and accuracy of interpretation can be improved.
【学位授予单位】：湖南科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U416.1;P631.3

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