| In the past people focused on such factors below of the major ground fissure in Xi'an ground fissure belt: Stratum formation, geological structural background, cause mechanism, activity law and so on, but paid less attention to the secondary fissure. Based on the seismic exploration results, it is proposed that the Xi'an ground fissure belt is generally composed by one major fissure and one secondary fissure. The secondary fissure, located on the up faulted block of the major fissure, has the normal fault property with north dip and north downthrown and merges into the major fissure with Y-shaped distribution, taking sedimentation influenced by the movement of the major ground fissure.To prove up the influence degree to the construction of Xi'an subway by the secondary ground fissure。This paper have taken analysis to the three-dimensional finite element model considering the major and the secondary ground fissure at the same time, comparing with the one with the major fissure only. It is found that the structure's factors blow of the model considering the sedimentation of the major and the secondary fissure seems bigger than the other one: vertical displacement, longitudinal stress, vertical shearing stress, equivalent of plastic strain and relatively displacement of soil body, when the distance between the major and the secondary fissure is near(generally 40-50m). Additionally the plastic distortion will occur earlier on the structure's bottom of the comparably complicated model and extend to the side wall rapidly. This course start earlier and develop rapider than that of the model considering the major fissure only. Based on the conclusion above it is suggested that if the distance between the major and the secondary ground fissure is bigger than 50m, the construction design for subway tunnel could consider the major and the secondary fissure as two independent fissures and take process according to their sedimentations separately.
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