溶洞在电阻率层析成像图中的成像特征及其解释推断？？
Imaging characteristics and interpretation for karst caves using electrical resistivity tomography

为研究溶洞在电阻率层析成像图中的成像特征，对江西省南昌―上栗高速公路沿线岩溶地层进行勘察，并建立相应的数值模型进行正演。在已勘明的溶洞中，分别选取大跨度空溶洞、大跨度填充溶洞、小跨度空溶洞及小跨度填充溶洞，观察其成像特征，分析得到不同厚跨比及填充情况下的溶洞在电阻率层析成像图中的成像特征，从而建立溶洞成像特征树图。模拟均匀空间中同时存在高阻介质和低阻介质的情况，并与勘察结果对比。最后在工程实际中应用溶洞成像特征树图，进行电阻率层析成像图的解释推断，同时结合钻探成果验证该方法的正确性。结果表明：高阻异常和低阻异常主要出现于大跨度空溶洞和大跨度填充溶洞，而在小跨度空溶洞和小跨度填充溶洞中并不明显；等值线弯折必然存在于填充型溶洞，且经常伴随低阻异常出现。数值模拟发现，等值线总是倾向于向低阻介质聚集，从而产生等值线弯折的现象；与此同时，由于电阻率等值线聚集于低阻介质附近，延伸受到很大限制，从而产生低阻屏蔽效应。在溶洞跨度较大的情况下，成像特征主要表现为高阻异常和低阻异常，解释推断较为简单；但在溶洞跨度较小的情况下，由于低阻屏蔽效应，小跨度空溶洞或较薄的溶洞顶板等高阻介质经常被遮盖，为解释推断带来较大困难。
To study the imaging characteristics of a cave using electrical resistivity tomography, the resistivity characteristics of karst strata along the Nanchang to Shangli Highway (Jiangxi, China) were investigated. Corresponding numerical models were established for forward modeling. In the karst caves that were identified, long？？span empty caverns, long？？span filled caverns, short？？span empty caverns, and short？？span filled caverns were selected for observation. The imaging characteristics of caves with different sizes and fillings were then obtained. A tree diagram for the analysis of the imaging characteristics of karst caves was proposed. The existence of high？？resistance and low？？resistance media in homogeneous spaces was simulated and then compared with survey results. Finally, the imaging feature analysis tree diagram of the karst cave was applied to engineering practice for interpretation of resistivity tomography images. At the same time, the correctness of the method was verified by drilling results. The results show that both high？？resistivity and low？？resistivity anomalies exist mainly in the long？？span empty caves and long？？span filled caves, rather than in the short？？span empty caves and short？？span filled caves. Contour line bending always exists in the filled karst cave and is often accompanied by low？？resistivity anomalies. The contours gather in the low？？resistance medium, which bends the contour lines. At the same time, owing to gathering of these resistivity contours near low？？resistivity media, the extension of which is greatly limited, resulting in low？？resistivity shielding effects. In short？？span caverns, owing to the low？？resistance screening effect, high？？resistance media such as short？？span empty caverns or thinner cavern roofs are often covered, which makes it difficult to explain. 10 figs, 25 refs.？