基于井间电磁CT探测的岩溶空间分布特征

Spatial distribution characteristics of karst based on cross hole electromagnetic computerized tomography technique

岩溶是桥梁桩基施工中的安全隐患之一,探明桥梁范围内岩溶的空间分布特征对桥梁安全尤其重要。岩溶勘查目前多以钻探与物探方法相结合,但特定的岩溶勘察需要根据具体情况选择合适的物探方法,常用的地质雷达等方法由于受限于各自的适用范围,往往不能精确地确定局部范围内溶洞的边界。井间电磁波CT探测技术主要依据电磁波在不同介质中传播时的吸收差异,重建井间介质吸收系数的分布图像,形象而直观地展现地质体内部结构,具有分辨率高,勘探距离小的特点,特别适合于探测桥墩等局部范围内的溶洞分布情况。以惠州S119线水西大桥主桥墩溶洞探测为例,介绍了电磁波法CT探测技术的原理、工作方法及应用效果,结果表明井间电磁波CT探测技术有较高的精度和可信度,可全面清晰地揭示场地岩溶的空间分布,为工程设计提供可靠的地质资料。

Karst is one of the hidden dangers in the construction of bridge pile foundation. It is particularly important for the safety of the bridge to prove the spatial distribution characteristics of karst in the scope of the bridge. At present, the exploration of karst is mostly based on the combination of drilling and geophysical prospecting methods. But the specific karst exploration needs to choose the appropriate geophysical method according to the specific situation. Commonly used geological radar and other geophysical prospecting methods often can not accurately determine the boundary of the local area of the cave due to their limited scope of application. The cross hole electromagnetic wave CT technique reconstructed the distribution image of the medium absorption coefficient of the wells base on the difference of the absorption of electromagnetic wave in different media. The image visually shows the internal structure of geological bodies. It has the characteristics of high resolution and small exploration distance. It is especially suitable for detecting the distribution of karst cave in the local area such as bridge pier. This paper introduces the principle, working method and application effect of the electromagnetic wave method CT detection technology by an example of detecting the karst of Shuixi bridge pier of highway S119. The results show that cross hole CT technology has high precision and reliability. It can fully and clearly reveal the spatial distribution of the karst, so as to provide reliable geological data for engineering design.