Abstract: As the operation side of the underground passage, the foundation trench is difficult to backfilled with an appropriate compacted after the completion of the main structure due to its narrow space and large depth. The traditional treatment method is inconvenient, while the compaction result is poor. The improper treatment could frequently lead to numerous post construction engineering problems, such as water-seepage and differential settlement, resulting in partial cracking and damage of the superstructure. From the underground passageway engineering construction, the study on the backfill treatment method of foundation trench of the underground passageway presented in this paper from the case history in Northwest China. Through the comparative study of different backfill approaches, the treatment method using the foam concrete is proposed, and the construction design method and technical aspects are elaborated in detail. Combined with the appearance test, physical mechanics test and settlement observation of the foam concrete after construction, the effect is evaluated. The results show that, the backfill treatment of the foundation trench by the foam concrete has a good appearance quality. Meanwhile, the strength and settlement aspects both meet the requirements. There is no seepage observed in the underground passageway, and no settlement cracks or faults are found in the superstructure. The results can provide a reference experience for similar projects, which have a great practical significance.

Key words: Foam Concrete, Underground Passageway, Foundation Trench, Strength, Settlement