Effect of Fatty Acids Addition into Backfilling Material in Over-cutting Area on Improvement of Lubrication Performance for Pipe Jacking

Background: The demand for underground space utilization using pipe jacking method is increased especially in the congested urban area. Methods: In the method, the over-cutting area is formed between pipes and surrounding soils in order to smoothly construct underground pipelines. The backfilling materials as a lubricant are injected into the over-cutting area during the constructions in order to reduce the friction resistance and to sustain the surrounding ground against the overburden pressure. Therefore, the performance of lubrication for backfilling material is significant. In this study, the fatty acids are added into the backfilling material to improve the lubrication performance. Conclusion: Laboratory studies have shown that the bleeding rate is reduced with the increase in addition ratio of fatty acids, however, the excess addition may cause the shrinkage of the backfilling material due to the effect of water absorption from the pipe. Additionally, 3% addition of fatty acids into the conventional backfilling material is the most effective to reduce the thrust for pipe jacking based on the results of the direct shear tests.