Abstract：Research purposes：
During the rebuilding lane close to existing railway, restricted by the driving interference and limitations of construction site and catenary headroom, reinforcement of soft ground is a difficult problem. Therefore, it needs a rational technology which  can  not only able to meet the limited space and subgrade settlement control requirements,but also ensure the existing railway safely operate.
Research conclusions：Bag reinforced grouting pile is a new technology using a combination of grouting technology, geotextile fabric and reinforced materials. The main advantages are followings: (1)The isolation of geotextile bag can make slurry to expand bag and compact soil. Reinforced grouting pipe as grouting channel not only simplifies the construction process，but aslo greatly enhances the shear strength and resistance deformation. (2)Construction uses the ordinary rotary drilling rig which has many advantages, such as appropriate adjustment according to the site, small footprint range, lower limitations of space and headroom. (3)The method of returning slurry from the hole bottom is adopted to construction by sub-section injection, repeatedly supplementary slurry, which can better ensure the pile quality. (4)The test results show that the bag reinforced grouting pile can not only ensure the shear strength and capacity, but also adapt the limitations of construction site and space and headroom, it can be widely applied in the reinforcement of soft ground.