Study On Mechanical Properties And Structural Forms Of Segmental Joint Shear Keys On Immersed Tunnel

With the rapid growth of urban agglomeration scale in China,the construction of modern comprehensive transportation system of our country ushered in a period of great development.As one of the most convenient transportation channels connecting cities on both sides of the river and the sea,immersed tunnel is widely used in large-scale transportation hub projects.Tubes of the tunnel are divided into segmental and integral ones according to the position of joint.Segmental tubular joint has relatively flexible overall compatible deformation ability,which can reduce the cracking of tubular joint caused by temperature difference,shrinkage and creep of concrete.As an important mechanical structure of segment joint,the structural safety of shear keys is critical to the waterproof performance of the joint.Therefore,it is necessary to analyze the mechanical properties of the segment joint shear keys.Based on the immersed tunnel of Hong Kong-Zhuhai-Macao Bridge,the mechanical properties and structural forms of the segment joint shear keys are analyzed by means of model test and numerical simulation.The main research results are as follows:(1)This paper summarizes the research status of segmental joint shear keys on immersed tunnel,and concludes that mechanical and deformation characteristics of shear keys are very complicated due to its own structure and environment.By comparing and analyzing the relevant deformation measurement methods,the digital image correlation method in modern optical measurement technology is selected as the measurement method of model test,and the validation test is carried out with this method.(2)Considering structural forms of immersed tunnel in engineering prototype and test conditions of model test,the scheme of model test of shear keys is determined according to similarity theory.The results show that when the load is 2000 N,the position of the shear kers appears obvious compressive strain and diffuses in a circular form;when the load is 5000 N,the distribution profile of the tension strain at the position of the shear keys is clearly visible and diffuses in a 45 degree direction.With the increase of load grade,the strain distribution has not changed.(3)Further comparative analysis of strain distribution along the horizontal and vertical directions of shear keys.The results show that along the horizontal direction,the maximum tensile strain is located at the joint of tenon and side wall,and the maximum compressive strain at the left end is smaller than that at the right end,and the strain difference is related to the load grade.Along the vertical direction,there are large tension strains from the bottom to the top of the joint position,while the large compression strains are concentrated in the outer corner of the keyway.Comparing and analyzing the results of model test and numerical simulation,the trend of strain distribution is basically similar,which shows that the finite element method has certain reference value.(4)The structural forms of shear keys are numerically analyzed by finite element method,and the stress distribution characteristics of shear keys under different working conditions are obtained.The results show that increasing the height of the shear keys can reduce the maximum tensile stress at the side wall junction of the shear keys and increase the maximum compressive stress at the end.Reasonable setting of inclination angle and increasing the number of shear keys can reduce the stress concentration level of shear keys,and play a positive role in improving the stress state of segmental joint shear keys on immersed tunnel.