Contrastive Study On The Effect Of PHC And CFG Pile Composite Foundation Of Wuqing Section In Beijing-Tianjin Intercity Railway

To meet the requirements of foundation settlement and ensure the safe operation of the high-speed rail, PHC and CFG pile raft structure strengthening technology were applied in the soft ground along Wuqing section in Beijing-Tianjin Intercity Railway, which is the first passenger dedicated line designed at the speed of350km/h in China. The article made an analysis and contrast of these two foundation treatment effect, which mainly focused on the respects of pile-soil stress-sharing and subgrade settlement.The vertical bearing capacity of the single pile in Wuqing test section was analyzed at the beginning of the paper,comparing their pile-soil stress ratio,load sharing and sedimentation characteristics from three angles, which contained the theoretical comparison, field data and numerical simulation model.Finally,the optimum design parameters were obtained with the method of orthogonal experiment analysis,which provides a reference for the engineering practice.With the work above, the following conclusions were achieved:1. PHC pile plays a much better role in the aspects of single pile bearing capacity improvement and compaction effect from the view of reinforcement mechanism for both PHC and CFG pile composite foundation. Specially, phenomena such as channeling holes and broken pile occurring during the construction process of CFG pile can be avoided.2. Judging from the analysis of monitoring data got from Wuqing test section in site, the foundation treatment effect of PHC pile is quiet remarkable. Contrasted with CFG pile,the average settlement of the central PHC line decreases from-70mm to-40mm while its load sharing between the pile and soil increases from0.505to0.67.3. Simulation results show that the average ratio of PHC pile composite foundation increases from0.62to0.71while its average settlement of the central line decreases from-63.61mm to-38.14mm.4. After optimization for the design parameters of the PHC pile composite foundation, the optimal values comprising the pile length of18m, pile spacing of1.5m, pile diameter of0.4m and the pile modulus value of30000MPa were achieved.Meanwhile,the optimal parameters of the cushion consisting the sickness of0.3m, modulus value of50Mpa and the Poisson's ratio of0.30were also summarized.