Research methods: The method of impact rolling compaction to accelerate settlement with the four sectors and eight flows was adopted to fill the subgrade，the ways of K30，Ev2and Evd were adopted to examine the subgrade compactness, the methods of laying settlement plate and section plane tube were adopted to trace and observe the change of subgrade settlement for long term and record the data on settlement volume, and the software was compiled to predict the regularity of settlement change.
Research results: The design requirements of compactness were met for the subgrades in pile-net reinforcement section and red rock mudstone improved section. The observation results from settlement plate showed the total predicted settlement volume was less than 15 mm and the settlement volume in six months was less than 8 mm, which met the requirement for post-construction settlement volume of 15 mm. The uneven settlement volume of 20 m was 7. 89 mm , which met the requirement of 20 mm/20 m.
Research conclusions: The subgrade construction was done by technologies mentioned above passed the evaluation of subgrade and met the requirement of ballastless track of 200 km/h railway.
2007, Vol. 24 
