点状不良地质体钻孔雷达响应特征 ——围岩及充填效应正演分析

钻孔地质雷达探测是一种有效获取高分辨率深部岩体信息的井中地球物理方法。针对钻孔地质雷达探测工作中常见的空洞、岩溶和地下埋藏物等点状不良地质体，利用时域有限差分数值模拟方法，对岩土体内点状不良地质体围岩介质和充填状况进行了雷达响应正演研究，分析了这些点状不良地质体围岩介质和充填状况对钻孔地质雷达反射信号的影响。研究结果表明，围岩与空洞内充填物的相对介电常数相对值，决定着雷达反射剖面信号的强弱对比，介电常数相对值较大时，更易确定目标地质体的前、后部界面位置，而低阻围岩的雷达波信号大部分被围岩介质吸收，通过单孔反射方法几乎不可能探测到空洞的存在。通过反射信号强度和正负相反射特性及其强弱变化，可以定性地判断空洞内填充物质的性质。

Borehole radar response characteristics of point unfavorable geo-bodies: forward simulation of its surrounding rock and filling condition

Borehole radar is a well geophysical method for obtaining the high-resolution information of deep underground environment.According to the common point unfavorable geo-bodies in borehole radar exploration,such as cavities,karst caves and buried objects,etc.,the forward simulation of response of the tool to point unfavorable geo-bodies of different surrounding rock and filling condition is investigated with finite difference time domain(FDTD) method.The influence of surrounding rock and filling condition on response characteristics of borehole radar is analyzed.The results indicate that the relative value of dielectric constant of surrounding rock and filling substance affects the contrast of radar reflection profile,and when the relative value of dielectric constant increasing,it is easier to ascertain the subsurface media distribution.While high-conductivity surrounding rock can attenuate most of radar signal,it is almost impossible to detect the cavities with single borehole reflection method.According to the different borehole radar cross-sectiorn and its response characteristics,the filling condition in the cavities can be qualitatively distinguished.