| To satisfy the rapid development of economy and transportation, the Closely-spaced Tunnel seems very demanding and its convinent to be connected make it widely to be used. Due to complicated topographical and geological conditions as well as large numbers of mountainous areas, especially in Yunnan province with 94% of mountain areas, constructions of high-grade highway unavoidably meet with lots of tunnel works. Most of tunnels have complicated cross section and shallow depth when constructed in canyon zone. As the shallow depth and poor geological conditions, the surrounding rocks are always soft, fragmentized or intensively disintegrated rock mass with partial pressure. Additionally, with the interactions between two tunnels, the operational characteristics such as face pressure become complex. Therefore, this paper introduces a detailed analysis of different load-structure method troughs over twin tunnels.This paper based on the project of Pingnian Closely-spaced tunnel in Yunnan province. The paper is conducted using numerical analysis method that models the classical cross-section K7+439, many methods are adopted, such as ansylsing of ground surface settlement, crown settlement, interspaced rock stress and deformation, and so on, to discribe the character of various Load-structure over symmetric twin tunnels.The major factors which is improtant for symmetric twin tunnels, such as the distance between twin tunnels, the symmetric angle, the excavation order,the dislocation,were investigated thoroughly. With the aggregation, this paper put forward the the character of various load-structure over symmetrically loaded closely-spaced tunnels, which incorporates the support of the design and Construction of symmetric twin tunnels.
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