In recent years

some gravel soil tunnels avalanche along with the continual increase of base-building investment by the government. The stabilities of surrounding rocks of gravel soil tunnels which appearanced on the stocks of railway and highway were computed by using improved discrete element method software. Firstly

the self-stability of surrounding rock was analysed. Secondly

the relations between tunnel-stability and gravel diameter were discussed; and the limited-dig-span of tunnel of gravel diameters of 0.1 m

0.2 m

0.35 m

0.5 m

1 m

2 m were studied respectively. Finally

the relation between tunnel span and collapse quantity was computed.The method and result can give reference to the similar engineering.