Abstract：PHP (partially hydrolyzed polyacrylamide) slurry is especially suitable for the drilling of overlength and extra-large-diameter bored piles. Its economical efficiency and construction efficiency are dependent on the following key factors：manufacturing of raw materials，manufacturing process，cycling system and construction control. According to geological and hydrologic conditions of the site of Su-Tong Bridge，the testing pile project has adopted PHP slurry cycling system，which has been proved in the practice to have achieved thickness of mud cake around piles less than 1 mm and thickness of sediments at pile tip of zero.
