Abstract: Shenzhen Metro line 3 passes through the Guangzhou-Shenzhen railway viaduct so it is necessary to underpin the piled foundation of existing bridge and man-hole-piles are used, the project is in a saturated, loose sand stratum with high permeability and high confined water head.Two-shot grouting was used to form a waterproof curtain.By means of the experiment, determines the proportion was determined reasonably, the construction method was grasped and inspected the grouting effect inspected.The results of test and construction show that cement and water glass two-shot grouting in the saturated loose sand layer can increase strength significantly, and seepage coefficient be decreased by 102~103 magnitude, the hydraulic fracture pressure of the soil curtain is more than 0.3 MPa and surface deformation is small, thus meeting the waterproof requirement of 2 m diameter and 24 m long man-hole-pile completely.