Yield Stress Mechanism of Composite Support System at Swelling Rock Tunnel Buffer Layer
To build the theoretical model of buffer layer composite support system,the yield stress mechanism of buffer layer composite support system was analyzed to make up for the limitations of current buffer layer yield stress mechanism.The three-layer thick-wall cylinder model was constructed based on the single-layer thick-wall cylinder model with elasticity knowledge.The functional relation between the support structure stress and the external load in buffer-layer composite support system was deduced.The correctness of analytical solution of stress on the buffer-layer composite support structure was verified by using numerical simulation.Based on this theoretical model,the stress characteristics of secondary lining and the primary support in composite support system with or without buffer layer were analyzed.The yield stress mechanism of buffer layer was summarized.In the composite support system with buffer layer,the buffer layer material was compressed.The initial support would undergo greater inward deformation,thereby absorbing the external load,and reducing the secondary lining stress.Therefore the entire structure would achieve the compression effect.In other words,the composite support of buffer layer realized the compression through the buffer layer yield stress.By changing the thickness of buffer layer,the yield stress mechanism was analyzed.The result indicates that when the buffer layer thickness is 5 cm,the deformation of initial support increases by 1.34 cm,and the force transferred to the secondary lining is reduced by 71.6％.When the buffer layer thickness increases to 10 cm,the secondary lining force is further reduced,which is more favorable to the secondary lining structure.In the yield support system,when the buffer layer is compressed,the internal stress of initial support also increases.In particular,the circumferential stress(i.e.,the yield stress of buffer layer)is disadvantageous to the initial support,and advantageous to the secondary lining stress.Therefore,in the composite yield support system,when the external force is constant,the stress of initial support and second lining should be considered in the buffer layer design;that is,there is an optimal value of buffer layer thickness.
tunnel engineeringyield stress mechanismthick-wall cylinder modelbuffer layerswelling rock
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