Detection Method of Pile Foundation on Subway Lines Based on Cross-Hole Resistivity Computed Tomography

Abstract

When urban subway lines pass under buildings, it is often necessary to carry out corresponding pile foundation detection work to ensure construction safety. However, detecting the distribution of piles with conventional surface geophysical techniques is not an easy task because of space constraints. The cross-hole resistivity computed tomography (CT) method only needs two drill holes to implement the detection, which can overcome the difficulty in arranging the survey line above the pile foundation. Moreover, this method is suitable for low-resistance body detection, with the advantages of high detection accuracy and less influence from ground interference. In this paper, six types of geoelectric models are constructed for numerical simulation analysis due to two major factors that affect the detection effect of cross-hole resistivity CT: model parameters and measurement parameters. The results show that cross-hole resistivity CT provides an accurate imaging of the shape and distribution of the pile foundation between the holes. Furthermore, the technique provides a good detection of the bottom interface of the pile. The detection effect is best when the electrode spacing is 1 m, the pile is located in the detection center domain, the borehole spacing control is not more than 20 m, and the pile drill hole spacing is not less than 5 m. The research results have effectively guided practical engineering applications and obtained good detection results. The theory and practice show that the cross-hole resistivity CT is a more feasible method for detecting pile foundations on subway lines.