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| Universal Calculation Method for Design Values of Tunnel Surrounding Rock Pressure under Different Burial Depth Conditions |
| XU Chen1, XIAO Mingqing1, XIE Biting1, WANG Kejin1, CUI Lan2 |
| 1. China Railway Siyuan Survey and Design Group Co. Ltd, Wuhan, Hubei 430063, China; 2. Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei 430071, China |
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Abstract Research purposes： The calculation of surrounding rock pressure is an important link in the quantitative design of tunnel supporting structure. There are obvious deficiencies in the current research, such as the abrupt change of surrounding rock pressure at the boundary of deep and shallow burial and the constant value of surrounding rock pressure at the deep burial stage, which are inconsistent with the practical cases. Therefore, the concept of design value of surrounding rock pressure is introduced in this paper, and a general method of design value of surrounding rock pressure based on failure mode of surrounding rock is proposed, which can provide theoretical guidance for the tunnel design under various burial depths. Research conclusions： (1) The method in this paper seeks the design value of surrounding rock pressure by calculating the ultimate equilibrium state of rock mass approaching or reaching the failure stage and the load in the failure zone, which has the universality to different tunnel characteristics. (2) The load evolution law of the support-failure zone is different in tunnel from shallow to deep, resulting in great differences in the pressure characteristics of surrounding rock. The support-failure zone load curve of shallow buried tunnel goes through four stages successively: full soil failure stage, compression shear failure stage on both sides, compression shear failure stage around the tunnel, no failure stage or local failure stage. The first two stages are dominated by slack load. The latter two stages are dominated by deformation pressure. When it is between the two stages, it is necessary to make a comprehensive judgment according to the tunnel limit equilibrium state and take the envelope value. The method in this paper can ensure the continuity of the calculation results of tunnel surrounding rock pressure changing with the buried depth. (3) Comparing to Code for Design of Railway Tunnel, the design value of surrounding rock pressure calculated by this method agrees better with that in the practical engineering, and has higher rationality and reliability.
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