Abstract: The horizontal directional drilling (HDD) method used in trenchless pipe excavation is employed in tunnel geological survey to overcome the shortcomings of traditional drilling survey methods and more accurately derive information and stress distribution characteristics of the rock mass from tunnel surrounding. Detailed technical solution derived from the HDD method can be summarized as follows: After boring a HDD survey hole along the tunnel′s design axis, intermittent coring and tests, such as hydraulic fracturing, comprehensive logging, and downhole television are performed, and the test results are used to accurately identify the lithological variation of surrounding rock along the tunnel′s design axis, the distribution range of fracture zone, and the water inrush condition in the tunnel. Furthermore, the HDD method is used to investigate the geology of the Tianshan Shengli tunnel. Finally, coring and boreholedownhole television are conducted in a 2 271 mlong HDD survey hole. The results confirm the feasibility and efficiency of employing HDD technology in tunnel geological surveys.

Key words: tunnel, geological survey, horizontal directional drilling (HDD), highdefinition drillhole television