Abstract: In order to investigate the deformation of pipeline during tunnel excavation， the relations between the macroscopic and microscopic parameters of pipelines were formed based on laboratory deflection test and PFC programming. Based on the PFC2D， the numerical model of the tunnelsoilunderground pipeline was established for simulating the deformation of pipelines during tunneling in sand， and the effects of ground loss and tunnelpipeline space were examined. The numerical results showed that the behavior of pipelines is negative downdrag in the middle and positive downdrag at 35 times the diameter of tunnel from the middle of pipelines， which are greater under the increase of ground loss and decrease of tunnelpipeline space. With increasing ground loss and decreasing tunnelpipeline space， the additional load on the top of pipeline increases and the vertical earth pressure decreases quickly at the bottom of the pipeline， which trends to reach a final value. The ratio of ip/i as the width coefficient is proportional to the ground loss， and inversely proportional to the tunnelpipeline space， where the maximum value of 24 can be reached.

Key words: tunnel excavation, pipeline, PFC2D, settlement, sand, additional load