Abstract: K15+838.35～+660 section of the trial section of the first phase of line M3 of Qingdao Metro, with 8.15~13.1 m overburden, runs through Grade VI waterrich sand strata. Furthermore, the tunnel section has complex ground surface environment. Therefore, there is great risk in the construction of the tunnel section. However, dewatering and vertical reinforcement can not be executed from the ground surface. Therefore, horizontal jet grouting piles, as well as a series of advance reinforcement technologies are adopted, so as to guarantee the safety of the surface buildings and the tunneling labors. The disadvantage of horizontal jet grouting piles in sand strata and crushed stone strata, i.e., failure in interlocking, is solved, which guarantees the safety of tunneling in waterrich soft ground.

Key words: Metro tunnel in waterrich soft ground, horizontal jet grouting pile, waterrich sand strata, pile interlocking, grouting through advance small duct