| Summary: | The city fast track railway bridge studied in this paper is located above an old mined out area. There is a 1500m2 underground goaf in the construction site with a depth of 30.8~53.2m, the seam thickness is 2.0~2.5m and the dip angle is 50~63 degrees. Although the mine has been abandoned for many years, there are still a lot of underground cavities. Collapse pits occurred on the surface occasionally till this day, especially during the rainy season. In order to make the design safe and reliable, drilling pressure grouting technique is proposed to fill and reinforce the foundation of the site. Proposed technique is tested by several experiments in simulated underground mined out area for the foundation treatment. The technical design, construction technology, grouting and reinforcement effect of the project are studied and summarized. The results of the experiment showed a stable and safe bridge foundation has been achieved. The proposed technique was then applied to on site experiment and pasted all tests.
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