Study On Spatial Distribution Stress Of Foot Blade During Caisson Sinking In Water

Since the reform and opening-up,the national economy has been rapid development,science and technology has made rapid progress,in response to the needs of the times,the needs of economic development,the needs of people’s lives,a long-span Yangtze River Bridge is springing up like bamboo shoots after a spring rain.The construction of the bridge can not be separated from the pier foundation.with the development of technology,caisson technology has been gradually applied to the construction of piers.the caisson has good integrity and stability,and is not only the foundation but also the retaining and water retaining structure during construction.However,the caisson has high requirements for construction,and it will encounter the problems of sudden sinking,inclined and difficult to sink when sinking.At present,the size of the caisson is getting larger and larger,which requires a more accurate grasp of the sinking accuracy of the caisson in construction and a fuller understanding of the sinking law of the caisson,but at present,there is little research on the super-large caisson.If we master the change law of the bearing capacity of the edge and foot in the sinking process of the caisson,we can understand the law of the sinking of the caisson through the change of the bearing capacity of the edge and foot,provide a reference for the construction of the caisson in the future,and make adjustments in time by monitoring the change of the bearing capacity of the edge and foot.Avoid sudden sinking of caisson,tilt and other problems.Based on the research and development project of science and technology of China Railway Corporation,"Research on key Technologies of Design and Construction of Ultradeep and large Section caisson",this paper takes the caisson of No.29 main pier of Hutong Yangtze River Bridge as the background.By means of indoor scale model test and field edge foot earth pressure analysis,the spatial distribution characteristics of edge foot bearing capacity in the process of caisson sinking are studied.The main conclusions are as follows:(1)The variation law of the effective stress of the blade pedal surface affected by the sinking depth,sinking rate,sudden subsidence and inclination of the caisson is obtained.The variation trend of effective stress measured at all points on the same side is generally the same.With the increase of the sinking depth,the effective stress of the blade pedal shows a fluctuating downward trend,and the effective stress of the pedal increases when the sinking of the caisson stops.When the sinking rate of the model is low,the effective stress of the blade pedal increases,and when the sinking rate is accelerated,the effective stress decreases rapidly.When the model encounters sudden sinking,the effective stress of the tread before the sudden sinking will rise,and the effective stress will decrease rapidly after the sudden sinking.When the inclination of the caisson is changed,the effective stress on one side of the sinking rate becomes smaller,and the effective stress on one side of the sinking rate decreases and the effective stress on one side of the edge foot increases on the opposite side of the open caisson.Through this law,the sinking state of the caisson can be understood by monitoring the effective stress change of the blade pedal surface in the project.(2)According to the model test,the spatial distribution law of the effective stress on the blade pedal surface in the sinking process of the open caisson is obtained.Taking the effective stress at the midpoint of the long edge as the reference stress P,the overall force increase coefficient of the open caisson is obtained.The effective stress is 2.5p at the midpoint of the long edge and the midpoint of the short edge,4p at the quarter point of the short edge,and 7p at the corner.The data obtained from the pedal surface of the open caissons on the 29 # main pier and the monitoring results of the pneumatic caissons by Geu-guwen Yea are compared with the experimental results,and the conclusion is consistent with this conclusion.(3)The variation law of effective stress on the inclined plane of the blade foot is obtained.In the initial stage of subsidence,the effective stress on the inclined plane of the blade foot has little change,and the fluctuation variation range is within 5kPa.In the whole sinking process,the change trend of the effective stress of the blade foot tread is opposite to that of the inclined plane.When the sinking of the caisson is slow,the effective stress of the blade foot slope decreases,the effective stress of the tread increases,and the effective stress of the blade foot slope increases when the sinking is accelerated.The effective stress of the tread is reduced.(4)The curve of the effective stress between the bevel of the blade and the tread is obtained.The curve of the relationship between the horizontal distance from the inner edge of the tread and the effective stress of the inclined plane is obtained.the fitting curve is a cubic curve.In engineering,the effective stress of the inclined plane can be calculated by measuring the effective stress at the tread and the height of the mud surface at the inclined plane.(5)The distribution law of the bearing capacity of the blade pedal surface is obtained,which accords with the form distribution of the quadratic curve y = ax ^ 2 + b,and calculates the position of the average value point of the effective stress on each side.If the length of the side is 2L,the mean point of the effective stress is 0.58 L from the center.According to the fitting curve,the average effective stress ratio of the tread to the inclined plane at the same position of the edge foot is 4 to 1.For the calculation of the resistance of the edge foot of the open caisson,it is more reasonable to calculate the edge foot surface and the inclined plane respectively.