隧道前方不良地质体探地雷达正演模拟研究

探地雷达正演模拟是反演和剖面判释技术的基础,是人工识图的依据,可以提高图像解释的精度和准确度。从概括宏观电磁场规律的Maxwell旋度方程出发,运用Yee网格模型和中心差分公式,通过引入复介电常数,推导了二维单轴各向异性理想匹配吸收边界的电、磁场离散差分公式,并用MATLAB语言编写了基于单轴各向异性理想匹配吸收边界的二维横磁波探地雷达数值模拟程序,运用该程序对隧道前方断层破碎带、方形和圆形溶洞进行了正演模拟,揭示了不同地质体的图谱特征、反、绕射规律和传播特性。模拟结果表明：单轴各向异性理想匹配吸收边界能有效抑制差分网格截断边界处非物理因素反射,很好地突出有效波,更便于工作人员依据图谱准确地进行地质解释。

Study on Forward Simulation of Ground Penetrating Radar for Unfavorable Geologic Body in Front of the Tunnel

Ground penetrafing radar （GPR） forward modeling is the basis of inverse modeling and the identification technology of profile. GPR is also the basis for artificial reading engineering drawings. By using it the precision and accuracy in explaining images can be improved. From Maxwell＇ s Equations of rotation which summarizes macroscopic electromagnetic theory, using Yee Network Model and central difference formula, by introducing complex permittivity, the authors deduce two-dimensional UPML absorbing boundary of electromagnetic field discrete difference formula. The forward modeling program based on UPML absorbing boundary two- dimensional TM wave is realized by programming language MATLAB. The forward simulation of crushing zone in front of the tunnel and square, round cave is conducted by using the program. Profile features of different geological bodies, rule of reflection, rule of diffrac- tion and propagation characteristics are revealed., The simulation results show that UPML absorbing boundary could effectively inhibit the non-physical reflection of truncating boundary to outstand the effective wave, which is beneficial for engineers to accurately make geological interpretation with the map.