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Load-Bearing Stages of Joint Shear Keys and Settlement Control Standards of Immersed Tunnel Elegments
(1 School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang 050043; 2 School of Highway, Chang′an University, Xi′an 710064; 3 The Key Laboratory for Health Monitoring and Control of Large Structures, Shijiazhuang 050043; 4 Power China Huadong Engineering Co. Ltd., Hangzhou 311122)
Abstract Shear keys are the main load-bearing components for resisting expansion and rotation of elegment joints and are a structural guarantee of joint waterproofing when differential settlements of foundations occur because of load or soil layer factors. Therefore, differential settlements were taken as the variable loads in 1∶4.69 large-scale model tests and 3D FEM numerical simulations to study the load-bearing laws of shear keys on elegment joints affected by differential settlements. The test results show that the load-bearing processes of shear keys can be divided into three stages under the effects of longitudinal and transverse differential settlements. In the first stage, gaps and rubber pads between the shear keys and their grooves start to be compressed, and the stress growth rate is relatively small. In the second stage, shear keys undertake loads effectively and the stress growth rate is much larger, comparatively, while the elegment joints help the shear keys undertake loads through local compression or friction when differential settlements reach a certain extent. In the third stage, shear keys are inclined to yielding, and though shear keys can still bear more loads, micro-cracks occur. Based on the shearing forces of shear keys in the limited state of normal use, the longitudinal and transverse allowable differential settlements of elegments are determined as 11.5 mm and 11.1 mm, respectively. It is recommended that several prestressed cables on the roof and floor of the elements remain after immersion in order to improve the structural safety of the shear keys.
Abstract：
Shear keys are the main load-bearing components for resisting expansion and rotation of elegment joints and are a structural guarantee of joint waterproofing when differential settlements of foundations occur because of load or soil layer factors. Therefore, differential settlements were taken as the variable loads in 1∶4.69 large-scale model tests and 3D FEM numerical simulations to study the load-bearing laws of shear keys on elegment joints affected by differential settlements. The test results show that the load-bearing processes of shear keys can be divided into three stages under the effects of longitudinal and transverse differential settlements. In the first stage, gaps and rubber pads between the shear keys and their grooves start to be compressed, and the stress growth rate is relatively small. In the second stage, shear keys undertake loads effectively and the stress growth rate is much larger, comparatively, while the elegment joints help the shear keys undertake loads through local compression or friction when differential settlements reach a certain extent. In the third stage, shear keys are inclined to yielding, and though shear keys can still bear more loads, micro-cracks occur. Based on the shearing forces of shear keys in the limited state of normal use, the longitudinal and transverse allowable differential settlements of elegments are determined as 11.5 mm and 11.1 mm, respectively. It is recommended that several prestressed cables on the roof and floor of the elements remain after immersion in order to improve the structural safety of the shear keys.
.Load-Bearing Stages of Joint Shear Keys and Settlement Control Standards of Immersed Tunnel Elegments[J] MODERN TUNNELLING TECHNOLOGY, 2018,V55(4): 132-138
2018, Vol. 55 