Resistance And Suddenly Sinking Monitor Research Of Deep And Large Open Caisson Of Hu Tong Bridge

As the country's economic take-off, large span bridge construction has become an important part of modern transportation development. Open caisson is a reliable form of deep foundation because of its high bearing capacity, good entirety, stiffness and widely geological conditions has been extensively applied to large span bridge pier foundation and anchorage foundation. But the study of deep and large open caisson is still relatively lack. Based on the world's largest caisson foundation construction as the background, to carry out on-site monitoring test, analysis of monitoring data, research the open caisson sinking and stress condition in the construction period. The main research contents and conclusions are as follows:(1) The end earth pressure of deep and large open caisson is numerical fluctuate when sinking, and stable when heightening. When the open caisson sinking, the soil pressure measured under limit close to the limit of bearing capacity of soil.(2) The distribution of lateral compression of deep and large open caisson is an extremely complicated problem. It refers to the attitude and buried depth of open caisson, the lateral steps set radius of caisson, stress relaxation of foundation bed and other factors during sinking and heightening. When the open caisson is vertical state during sinking, the distribution of lateral compression is the upper small steps big edge foot in times. Because of the high ground stress, stress relaxation effect will be slow to recover, and the buried depth, the greater the stress relaxation impact range, the greater the recovery is slow during heightening. Tilt will cause the distribution of lateral pressure change during sinking and heightening. Different side and ipsilateral buried depth exist increase earth pressure because of tilt.(3) The existing calculation method in deep and large open caisson sinking resistance theory has limitations in application. Combining with the field measured data and the construction condition of considering the ultimate bearing capacity coefficient of correction, the buried depth of open caisson, open caisson and stress relaxation effect of the tilt correction algorithm in Shanghai tong bridge deep large open caisson sinking resistance calculation on application has a good result. Small cross(40×30m) section of side friction resistance of unit area per unit area of open caisson pile side friction between 40 to 60kPa, large cross (90×60m) section per unit area of open caisson pile side friction between 75 to 85kPa,3 to 4 times for the current specification values.(4) By monitoring and statistics found that the sinking process of deep and large open caisson is not always smooth, but with sudden sinking and sand gushing, the way of open caisson sinking is the combination of sudden sinking, sand gushing and swinging as "pendulum" sink.(5) According to the measured soil pressure data of sudden sinking and sand gushing, the paper explains the reason of sudden sinking and sand gushing. And using the advanced numerical change of earth pressure, sinking resistance correction algorithm to first put forward sudden sinking early warning mechanism.