Techniques to Monitor Caisson Sinking Construction of Pier No.6 of Changtai Changjiang River Bridge
The main navigation channel bridge of Changtai Changjiang River Bridge is a rail-cum-road cable-stayed bridge with a main span of 1 208 m.The pier No.6 is supported by a giant stepped caisson foundation of a steel shell and concrete composite structure that needs to sink through the intersected clay and soil layers.In plan,the caisson is round-ended,measuring 95.0 m by 57.8 m,with the height reaching 72.0 m.To effectively control the sinking construction risk and improve caisson sinking efficiency,a control philosophy of"one dominant alignment and three constraints"was proposed.Considering the constructability,the uplift monitoring points were arranged in the interior and exterior caisson walls as well as the treads of cutting edges,to satisfy the demands of sinking resistance calculation,foundation soil erosion prediction and soil excavation effect evaluation.An empirical algorithm based on cone penetration test(CPT)to evaluate the reaction forces at treads of cutting edges of exterior caisson walls was proposed,to calculate the bottom resistance of the caisson during the sinking process.To elucidate the significance of the sinking factor and accurately evaluate the sinking feasibility,itemized calculation of the sinking resistance and state-based sinking feasibility evaluation were employed.An arc-sliding-theory-based method was utilized to evaluate the foundation soil stability,finding that controlling the reaction forces of treads of the cutting edges below 1.0 MPa was critical to the foundation soil stability.To bring the attitudes of the caisson under control,the portion of lateral resistance during sinking in the total sinking resistance must be taken as the judging index of abrupt sinking risk,and for the Changtai Changjiang River Bridge,the abrupt sinking risk was low.By taking the measures,the caisson of pier No.6 sank smoothly and expeditiously into position.
cable-stayed bridgestepped caisson foundationsettlement feasibilityfoundation soil stabilityattitudesafety controlconstruction monitoring and control
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