Construction Techniques for Foundation of Main Pier No.3 of New Baishatuo Changjiang River Bridge

The main bridge of the New Baishatuo Changjiang River Bridge is a steel truss girder cable-stayed bridge with span arrangement(81+162+432+162+81)m.The foundation for the main pier No.3of the bridge is the one that is comprised of 36 nos.of3.2mbored piles and the dimensions of the pile cap is 67.4m×31.3m×6m.In comprehensive consideration of various factors in the construction,it was determined that the foundation should be constructed by the scheme of the"underwater controlled blasting+multi-function platform+double-wall steel boxed cofferdam".The underwater blasting was carried out in parallel with the assembling of the multi-function platform.The construction of the bored piles and the assembling of the doublewall steel boxed cofferdam were carried out also in parallel in separated double levels.In the underwater blasting,the emulsion explosive was used.The multi-function platform was integrally floated to the pier site,was lifted in place,using the technique of multi-point and synchronous lifting and together with the flood controlled piles at the pier site,the boring platform was formed.The steel casings for the bored piles were inserted and driven by the vibration pile driver.The holes of the bored piles were constructed by the method of clear water ail lifting and reverse circulating.After the cofferdam was well assembled,the cofferdam was filled in with water and was ready to sink down,the leakage in the cofferdam was stopped,the cofferdam was riprapped and backfilled and the base sealing of the cofferdam was constructed.The platform was then lowered down and transformed into the internal support and finally the water in the cofferdam was pumped out and the construction of the pile cap was carried out.