本文選題：土質(zhì)路基 + 介電常數(shù)　； 參考：《湖南科技大學(xué)》2014年碩士論文

【摘要】：土質(zhì)路基含水量是整個(gè)路基路面強(qiáng)度和穩(wěn)定性的重要影響因素，通常采用鉆孔取樣等方法進(jìn)行測試，結(jié)果準(zhǔn)確、可靠，但成本高、效率低、代表性差，對既有道路、特別是營運(yùn)中的路段而言，這種破損檢測方法實(shí)際上很難實(shí)現(xiàn)。 探地雷達(dá)法是以電磁波傳播理論為基礎(chǔ)，以介質(zhì)電性（導(dǎo)電性和介電性）差異為前提的探測技術(shù)，而介質(zhì)含水量差異越大其電性差異就越明顯，因此，可以用該方法來研究地下介質(zhì)的含水性。本文基于探地雷達(dá)探測理論和方法，研究路基土含水量與介電常數(shù)的關(guān)系，試圖建立二者之間的經(jīng)驗(yàn)公式，為運(yùn)用探地雷達(dá)方法研究路基含水性提供理論和方法支持。 本文采用基于時(shí)域有限差分法的GPRMax2D軟件，建立了不同含水量、不同介電常數(shù)及典型病害類型的單層、多層介質(zhì)模型，模擬分析了電磁波的相位、振幅、雙程走時(shí)等響應(yīng)特征和規(guī)律，即：路基土含水量增加會(huì)使介電常數(shù)和電導(dǎo)率變大，使電磁波的傳播速度變小，表現(xiàn)為同一深度的雷達(dá)回波的雙程走時(shí)增大；當(dāng)電磁波由介電常數(shù)小的介質(zhì)入射到介電常數(shù)大的介質(zhì)時(shí)，反射系數(shù)為負(fù)值，其反射波的相位與激發(fā)電磁波的相位相反，反之亦然；當(dāng)上下界面的介電常數(shù)相差較大時(shí)，反射系數(shù)的絕對值也較大，會(huì)引起電磁波的強(qiáng)反射；電導(dǎo)率越大對電磁波的吸收越明顯，使其振幅變小；但電導(dǎo)率的差異不會(huì)影響雷達(dá)電磁波的傳播速度。 為了采用探地雷達(dá)測定路基土的含水量，在數(shù)值模擬的基礎(chǔ)上設(shè)計(jì)了物理模型。通過改變模型介質(zhì)的含水量，，獲得電磁波在不同含水量介質(zhì)中的傳播速度，再根據(jù)低損耗介質(zhì)中電磁波速度與介電常數(shù)的關(guān)系求得介電常數(shù)，分析、統(tǒng)計(jì)、擬合出土體含水量與介電常數(shù)的數(shù)學(xué)關(guān)系式。與常用的Topp、Alharathi等經(jīng)驗(yàn)公式模型進(jìn)行了對比分析，其結(jié)果具有一致的趨向性。結(jié)合實(shí)際路段雷達(dá)的探測結(jié)果，分析了路基的含水性及其對路基路面強(qiáng)度和穩(wěn)定性的影響。 研究表明，不同含水量的土質(zhì)路基的雷達(dá)響應(yīng)特征不一樣，含水量越大，反射信號雙程走時(shí)越長，幅度和頻率越低。通過多種模型的模擬分析，可加深對雷達(dá)反射剖面的認(rèn)識，有利于提高解釋精度和準(zhǔn)確性。
[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.
【學(xué)位授予單位】：湖南科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：U416.1;P631.3

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