基于GprMax的隧道超前预报雷达正演模拟及应用

GPR forward simulation for advance tunnel forecast based on Gpr Max and its application

针对隧道超前预报可能遇到的不同不良地质体,根据其介质电性特征,构建相应的地球物理模型,基于时域有限差分算法(FDTD)和完全匹配层(PML)的吸收边界条件,利用GprMax软件,结合matlab编程开展地质雷达正演模拟。研究结果表明,对于充填不同物质的溶腔模型,由于反射系数大小的差异,反射信号同相轴的强弱和形态有所不同,不同的地电模型其相位、振幅、波形特征都各不相同。结合2个工程实例,雷达正演模拟和实测剖面结果与实际开挖情况基本相符,验证了该正演方法的可行性,说明探地雷达能有效地勘察不良地质体的类型、位置、构造走向等空间分布特征,有助于更好地指导物探工作者对复杂地质体进行更精确的解释,确保隧道施工安全。

Advance forecast of geological conditions in tunnels may encounter different adverse geological body. According to the dielectric property of the geological body, a corresponding geophysical model was built. Based on Finite Difference Time Domain （FDTD） algorithm and Perfectly Matched Layer（PML） absorbing boundary conditions, GprMax software and MATLAB programming were applied to GPR forward simulation. The results show that the intensity and shape of the phase axis of the reflection signal in cavity filled with different substances is different due to the different reflection coefficients. The phase, amplitude and wave characteristics of different dielectric models are different. Combined with two engineering examples, the results of GPR forward modeling and measured profiles are basically consistent with the actual excavation, which proves that GPR can effec- tively detect the spatial distribution characteristics of adverse geological body, such as type, position, structure and strike and verifies the feasibility of the method. GPR is helpful for geophysical workers to explain the complex geological bodies more accu- rately, which will ensure the safety of the tunnel construction.