为解决山岭隧道勘察阶段因勘探孔数量少而难以较精准获取围岩性状的难题，以长沙某市域铁路山岭隧道为工程背景，提出基于微动探测与大地电磁联合物探识别围岩性状的方法。首先，参考前期勘察资料及地区经验，给出基于微动纵波和大地电磁法电阻率划定围岩级别、完整性和富水性的量化标准，并与现行相关规范对比验证该量化标准的可行性；其次，基于微动横波确定岩土层、土岩分界线，并计算得到微动纵波而后判定围岩级别及完整性；最后，利用大地电磁法电阻率圈定断裂带、节理裂隙带等特殊地质体和判定岩土层富水性，从而获取隧道围岩性状。与钻探、水文地质试验成果对比，结果如下： 1）微动横波可较高精度识别岩土层，误差基本在1 m以内，但对于岩性相近的风化岩误差相对大； 2）微动纵波划分岩体完整性的结论与钻探一致； 3）大地电磁法关于岩土层富水性的结论与水文地质试验结果基本一致。验证表明,在复杂地表、地质条件下, 微动探测联合大地电磁方法在隧道围岩性状勘察方面具有可操作性及其合理性。
This study addresses the challenge of accurately assessing surrounding rock properties during the surveying phase of mountain tunnels, which is often limited by the number of available boreholes. The authors propose a method that combines microtremor detection with magnetotelluric (MT) sounding. Using a mountain tunnel on a suburban railway in Changsha as a case study, the authors establish quantitative criteria for classifying rock mass grades, integrity, and water content based on microtremor P-wave velocity and MT resistivity, drawing on preliminary survey data and regional experience. The feasibility of these criteria is verified by comparing them with existing standards. The microtremor S-waves is utilized to identify soil layers, rock layers, and soil-rock interfaces, and microtremor Pwaves are employed to evaluate rock mass grades and integrity. In addition, MT resistivity is utilized to delineate geological features such as fault zones and jointed fracture zones, as well as to assess the water content of rock and soil layers, resulting in a comprehensive understanding of surrounding rock properties. The results are compared with those from drilling and hydrogeological tests. The key findings are as follows: (1) Microtremor S-waves accurately distinguish between soil and rock layers, with errors generally within 1 m, although greater discrepancies can occur in weathered rocks with similar lithology. (2) The rock mass integrity classification based on microtremor P-waves is consistent with drilling results. (3) The assessment of water content using MT resistivity aligns well with hydrogeological test results. These findings confirm that the proposed method is practical and effective for investigating surrounding rock properties in tunnels under complex surface and geological conditions.
