ABSTRACT
The freight railway line connecting Hailaer and Aershan in Inner Mongolia was improved to a passenger railway line, where roadbed surface layer was improved by the formation rehabilitation machine. Deteriorated ballast was reused after being crushed and mixed with river sand. Laboratory tests were conducted to firstly obtain the initial gradations of the aggregates including the deteriorated ballast, crushed deteriorated ballast, river sand and rock powder. Then the weight ratio of the crushed deteriorated ballast, sand and rock powder was investigated to make the mixed filler meet the gradation requirement specified in Chinese national railway criterion. The weight ratio was finally selected as 6:4:0 by considering the influence of seasonal freeze-thaw and wind-blow sand intrusion on roadbed stability. Field tests were also performed to obtain the sub grade reaction modulus K 30 and bearing capacity of the improved roadbed. The tested basic bearing capacity of the improved roadbed is 0.21 MPa and larger than the regulated lower threshold 0.18 MPa, which indicates that the weight ratio of the backfill aggregates provided by laboratory tests satisfies the compacting criterion.
