Abstract: The horizontal jet-grouting pile, which is applicable in soil reinforcement and water isolation, is hard to assemble an ideal homogeneous sealed pre-reinforced shell accounting for the restriction of geological condition, material characters and construction technology. For improvement, a composite pre-reinforcement technique utilizing horizontal jet-grouting piles and large pipe shed is proposed. The corresponding 3-D numerical model considering fluid-solid coupling effects is established using FLAC^3D for further analysis. The results show that the range of the plastic zone decreases by adding extra pipe shed beneath the piles. The “arch support effect” of piles in horizontal direction and “beam support effect” of shed in vertical direction can be fulfilled. With this technique, the value of the stretch stress of the horizontal rotary jet-grouting piles will be reduced, which results in better stability and reinforcement effect of piles. This technique is successful applied in the water-rich section of Jiangmen tunnel in Guangzhou-Zhuhai Railway, which may provide suggestions for similar projects.