Abstract：Abstract：Research purposes： The research on protection measures of subgrade isolation is weakly while the new or extension structures closed to existing ballastless track on high-speed railway subgrade. In particular, there is not special disposal measures and design methodologies for the introduction of existing ballastless track upon high-speed railway subgrade. To study the key solutions of the above mentioned issues, combined with the construction of Qufu-Linyi high speed railway, analysis of critical distance, subgrade fillers, foundation treatment and construction safety for the introduction of existing ballastless track on soil subgrade of Beijing-Shanghai high-speed railway is conducted. Research conclusions： (1) The isolation measures between new railway subgrade and existing ballastless track on high-speed railway subgrade can be neglected when critical distance is more than 50 m. (2) 0.6 m thickness gravel plus 0.6 m thick high strength reinforced lightweight concrete plus general lightweight concrete can be suggested as subgrade structure for the instruction of ballastless track. (3) The control effects of additional settlement for existing ballastless track on high-speed railway subgrade through micro steel tube pile was basically identical with cement fly-ash gravel pile, high-pressure rotary jet grouting pile and replacement of lightweight concrete. (4) The additional settlement of existing ballastless track on high-speed railway subgrade can be controlled effectively by using isolated piles, meanwhile, the control effects of additional settlement increased with the length of isolated piles, but small influence of spacing method. (5) The disturb of existing ballastless track on high-speed railway subgrade increased with the number of isolated piles excavated at the same time, therefore, the number of isolated piles excavated at the same time should be controlled reasonably. (6) The research results can be used as a reference method to introduce ballastless track upon high-speed railway subgrade．
2017, Vol. 34 
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