Abstract: The traditional vertical geological survey is often impractical in urban areas with dense buildings and complex surface environments. Therefore, directional drilling technology, which has already reached a relatively high level of maturity in geology, coal mining, and oil extraction, is introduced. Longdistance directional drilling is arranged along the underground engineering axis in this approach, explicitly using lateral hole drilling at critical geological points, and core samples at regular intervals are extracted. The specific measurement is obtained while drilling and comprehensive geophysical exploration is conducted in the drilling hole along the set trajectory to understand the formation lithology and geological structure of underground engineering area. Consequently, the surrounding rock lithology and tunneling and supporting parameters are determined. Based on the successful implementation of controlled track drilling for a 660 m mainhole and two 330 m lateral holes in Guangzhou urban area, the core drilling at an interval of 15~30 m is implemented and borehole acoustic wave and resistivity tests are used as supplements. Finally, the drilling core samples are compared with the results obtained through geophysical exploration to comprehensively assess the engineering geological conditions within a certain range of the tunnel.

Key words: tunnel, multiple branch, directional drilling, measurement while drilling, comprehensive geophysical exploration, geological investigation