某城市地铁隧道穿越既有桥台桩基，因桩基离地铁隧道轮廓线较近(约为1.0 m)，盾构施工时对桩基影响较大。为降低地铁隧道盾构施工风险，保证隧道顺利施工，需在施工前调查清楚桩基间距，为确定隧道盾构施工方案提供依据。由于地铁隧道地表交通、施工空间条件限制，只能采用地球物理方法进行探测。经过比选，采用3种跨孔CT法进行探测可满足要求。最后，根据探测结果在场区内进行钻孔验证，结果表明物探探测结果准确可靠。

An urban metro tunnel crosses the pile foundation of an existing bridge abutment; and the pile foundation is close to the contour line of the metro tunnel (about 1.0 m); hence, great impact would be induced by shield construction. In order to reduce the risk of shield construction and ensure the smooth construction of the tunnel, the distance between pile foundations should be detected before construction to provide the basis for determining the construction scheme of shield tunneling. Due to the limitation of the ground traffic and construction space condition, geophysical methods can only be used for detection. The comparison results show that by using three kinds of crosshole CT methods can meet relevant requirements. Finally, the borehole verification is carried out according to the detection results; the results show that the geophysical exploration results are accurate and reliable.