Construction of Very Long Rock Socketed Piles for North Pylon Pier of Edong Changjiang River Highway Bridge

The foundation for the north pylon pier of Edong Changjiang River Highway Bridge is composed of group piles.Totally 33 numbers of the bored piles,each 2.8 m in diameter in the overburden stratum and 2.5 m in diameter in the rock,are used.The length of a pile is 71 m and the depth of the piles socketed in the rock is 38~44 m.The ground conditions at the location of the foundation are complicated.In the construction of the piles,the KP3500 and Jintai GW-35 boring machines were used and the slurry for protecting the bored holes was the high quality PHP bentonite slurry.The boring of the holes was carried out in three stages in the steel casings,in the overburden stratum under the casings and in the rock further under the stratum.A bored hole was cleared off two times to ensure that the thickness of the deposited slag can meet the design requirements.A reinforcement cage was made in six sections in the same die by the long line method acciording to a standard section length of 12 m and was set in place by the jib crane.The tremie concrete for the bored piles was produced at a central batching plant and was delivered by agitating truck to the pier site where the concrete was then pumped into the bored holes through the rigid ducts.