The subgrade fill of some reaches of Qin-Shen Special Passenger Line consists of clean

round and poorly graded fine sand. For satisfied with “Detailed Rules and Regulations of Qin-Shen Line Railway Subgrade Construction Technology”

on the basis of a vast amount of comparative test

an economical and rational technical plan for improvement of fine sand is determined. According to the material proportion and construction technology

several millions of cubic meters of subgrade construction have been completed. A vast amount of technology data and rich experience for improving fine sand has been accumulated. Through analysis and study for improvement of fine sand

making further improvement on much respects has been found. On the basis of integration of theory with practice

this paper raises a calling in question for necessity of improvement of fine sand fill and control standard with a double targets; beside

reveals and sets forth essence of K30 value of poorly graded fine sand being on the low side and change regularity of fill strength as construction height.