Study on Application of Multi-level Yielding Support System in a Highway Tunnel in Soft Rock with Large Deformation
By using the technical concept of yielding support and using the Dujiashan Tunnel Project as an example,this paper is intended to investigate the response variation pattern of surrounding rock and support structure under dif-ferent combinations of yielding point and yielding quantity of multi-level yielding support.Also the supporting ef-fects of multi-level yielding support and one-level yielding support under their optimum yielding point and yielding quantity are compared.As the results indicate:If two-level yielding support is used and the yielding point and total yielding quantity remain unchanged,then as the first-level yielding quantity decreases,the secondary-level yielding quantity increases,and the horizontal displacement of surrounding rock,crown settlement,minimum principal stress and plastic zone all decrease before increasing.If the yielding quantity remains unchanged and the first-level yielding point increases,then the secondary yielding point gradually decreases,and the crown settlement,side wall horizon-tal convergent displacement and surrounding rock plastic zone all increase before decreasing,but with minor margin of variation.The minimum principal stress of surrounding rock decreases before increasing,so the deformation ener-gy released by the surrounding rock increases before decreasing.If a tunnel with large squeezing deformation is built with the two-level yielding support and the yielding quantity is released stage by stage,then the deformation energy released by the surrounding rock decreases.The support structure can effectively control the surrounding rock deformation.Stress redistribution of surrounding rock is adequately achieved.The stress and deformation of surrounding rock-structure under two-level yielding support system is more balanced than under one-level yielding support system.
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