In recent years, with the rapid development of city construction, pipelines have frequently been newly installed, relocated, and expanded. In general, embedment depth of the underground pipelines is usually relatively shallow, so the conventional methods can usually accurately locate them. However, locating the deeply buried metal pipes is a challenge since these deeply buried metal pipelines are often installed using the trenchless technologies such as microtunneling with large embedment depth up to 20 meters below the ground surface. Frequently, the embedment depth and orientation of the trenchless installed pipelines could not always accurately controlled. Therefore, the conventional geophysical shallow buried pipeline locating methods could not be effectively and accurately used in the deeply buried metal pipelines for their horizontal and vertical locations. Based on the comparison of several pipeline location methods, the downhole magnetic gradient method plus the corrosion detection apparatus was used in the locating of deeply buried metal pipes. The results were satisfactory.
