Deep Water And Super Large Open Caisson Foundation Construction Techniques In The Middle Pylon Tower Of Taizhou Yangtze River Highhway Bridge

Along with the construction of the bridge towards to the wide water area and open seas, more and more super-large bridges across rivers and straits came into being. As a common foundation for long-span Bridges, the open caisson foundation has a wide range of application prospect. Currently oversize deep-water open caisson foundation construction is facing many global problems in the construction technology, and also in domestic we have no design and construction practice to provide references, meanwhile research in this field is rarely reported. Foreign deep-water foundation construction techniques still should be carefully studied in combination with the domestic situation to satisfy our construction requirements .Therefore, I believe the research which relies on the open caisson foundation construction of the Tai Zhou Bridge project will have an important significance in the key technologies of theory and practice.According to the model test , field test, numerical simulation and theoretical analysis ,we are engaged in the research of open caisson float-conveyance, the riverbed scouring or silting problem, sinking position system, concrete pouring method ,bottom sealing construction craft, shimmy motion modality, construction safety monitoring system and construction risk assessment. Make discussions on the open caisson float-conveyance under the conditions of different water velocity, wind speed, different depth of water draught resistance and air resistance, and analyses the influence of riverbed scouring or silting towards to the open caisson accurate positioning. the influence of gravel size for different types of open caisson bits river bottom protection area after scouring characteristics were studied. By using numerical simulation and regulating the formula of "steel pier + anchor " of half rigid system is calculated and analyzed, and put forward some specific measures. Considering the caisson lateral friction function to the open caisson, we presented several bottom sealing crafts to choose and analysis,and also in combination with numerical analysis results ,studies of the influences to the riverbed caused by the concrete pouring construction are made. Open caisson under the different condition of wind speed, water velocity, shimmy motioning is discussed. Through the analysis of the whole process of the open caisson construction monitoring situation and qualitative analysis for each risk factor ,we proposed some new techniques and new methods for open caisson construction. The research shows that the air resistance from the windward slope and the inwall of the open caisson cannot be neglected during the float-conveyance of the open caisson, and alone with the speed increasing of the float-conveyance, the current obstruction function of the caisson becomes more and more evident. There exists some correspondingly relationship between the position of the open caisson and the scouring or silting of riverbed due to the changes of the flow force. To protect the caisson's riverbed, we have taken measures of dredging and filling to make the riverbed flat. And it could also increase the overall stability of the open caisson ensuring construction safety in flood season. As for the open caisson position, a half rigid system containing steel piers and anchors is helpful to make it accurate and easy to operate. But at the same time we should reduce the influence to the riverbed when we use this system. For the bottom sealing concrete pouring technology, we suggest that the adequate sequence for pouring should be the center first and then the four corners and the well nearby at last. According to the research that the open caisson should have been vibrate alone with its sinking because of its large weight and the impact caused by the flow force, In order to prevent it occurs we adopted some anti-vibration precautions. For the Safety as the open caisson sinking, we developed a real-time Monitoring and Controlling system which could monitor the open caisson's gesture anytime on the basis of GPS-RTK technology and presented a model for safety assessment. And also many precautions were presented to avoid risks after qualitative analysis on the influencing factor which may appear in the process of sinking construction.