Abstract: Loess tends to collapse or disintegrate under the cyclic load. Therefore, the operating train load might impose a safety threat to the construction of tunnel in loess soils near the existing rail lines. This paper presents a case history of a tunnel excavation in loess soils of Anjiazhuang Line near an existing rail line. The potential vibration induced settlement in loess soils surrounding the tunnel excavation was evaluated through the site-specific soil property testing. Compared with the original loess soil samples, the compression modulus of samples that subjected to vibration can reduce as much as 73% and the cohesion reduction of 43.5%. The internal friction of vibrated loess soils samples remained unchanged. The evaluation results indicated that the loess soil surrounding the tunnel excavation area can have 5 times greater settlement of the soils that without the vibration at the most unfavorable locations. The preventive measures included supporting the upper portion of the portal and lateral support of inside the excavation. These measures improved the safety of the tunnel excavation in loess soils. In the following excavation, early supporting and lining also played an important role in the successful tunnel excavation in loess soils.

Key words: Tunneling, Tunnel in Loess Soils, Mechanical Tests, Numerical Analysis, Construction Measures