During excavation of ultra-deep foundation pit off the west artificial island of the Hong Kong-Zhuhai-Macao Bridge,the piping of the foundation pit formed by the penetration of the pre-embedded pore water pressure monitoring instrument through the confined water layer was blocked by adopting the methods of high pressure jet grouting pile reinforcement,barite powder grouting,double liquid grouting and bag grouting.In this way,the problems of plugging at the initial stage of the piping point and the period when the piping path is obvious,were solved respectively.Especially,under the premise of no risk of collapse at the piping point,the plugging technology of grouting expansion along the piping path into the bottom of confined aquifer to achieve rapid water stop,skillfully solves the problem of piping plugging under high head difference.