In order to explore the mechanical characteristics of the combined lining structure of hydraulic tunnels laid with drainage board,an overall three-dimensional numerical model of rock-lining was established based on the finite element soft-ware ABAQUS.The constraints of surrounding rock,the contact nonlinearity of structural interface and the cracking nonlinearity of self-compacting-concrete were taken into consideration.The stress characteristics of steel pipe,self-compacting-concrete,segment and bolt under internal water pressure were thoroughly investigated.The influence of material property of drainage board on bearing capacity of structure was further discussed.The results show that the"transverse ellipse"deformation of the steel pipe occurs when the lining is filled with water,and an overall uplifting trend appears.The steel pipe at the end of the drainage board is in a state of bending and shear stress,and the overall stress level is low.The radial dislocation of self-compacting-concrete occurs after the end of drainage board cracks,and several penetrating cracks are distributed in the circumferential direction.Seg-ment deformation mainly occurs in the area without laying drainage board,and the annular direction is mainly in tension.The an-nular bolt has a large safety margin.The material property of the drainage board has a significant effect on the bearing capacity of the combined linings.With slight increase of elastic modulus of drainage board,the bearing ratio of the steel tube decreases obvi-ously and the bottom of self-compacting-concrete cracks,and circumferential tensile stress of the segment continues to in-crease,the combined lining shows an overall joint bearing trend,which is unfavorable to the segment.The later optimization design should focus on controlling the elastic modulus of the drainage board.It is recommended that the elastic modulus should not ex-ceed 10 MPa to ensure the safe operation of the lining structure.
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