Field measurement and CPT-based settlement prediction of existing railway subgrade reinforced by battered helical piles with grouted shafts

Abstract

In order to ensure the normal operation of the existing freight railway, it is difficult to adopt the common reinforcement measures (e.g., jet grouting or deep mixing) to meet the requirements. Reinforcement of existing railway subgrade by battered helical piles can meet the normal operation requirements of existing railways. However, there is no report on the research on the reinforcement of existing railway subgrade with battered helical piles. This paper reports on a field case study of railway subgrade improved by battered helical piles with grouted shafts (BHPGS) to mitigate the ongoing settlement due to temporary backfilling of subgrade without meeting the compaction requirement after heavy rain, which can be potentially harmful to the long-term operation of the railway. The measured coefficients of subgrade reaction (K30) of the 3 locations after BHPGS installation increased by 48 %∼166 % compared with the installation before. The long-term settlement of the railway subgrade reinforced with BHPGS was monitored by hydrostatic level and gradually stabilized after an adjustment period of about half a year, with the maximum settlement of 2.76 mm located at the center of the subgrade reinforcement section. In addition, a simplified method of calculating settlement based on CPT for the railway subgrade reinforced with BHPGS is proposed, with the calculated value of 2.99 mm in good agreement with the measured 2.76 mm.