Study On The Compacting Criteria Of The Railway Subgrade

The railway subgrade is the foundation to bear the track structure and train load, and whose compacting quality direct influent the transport safety and effectiveness. In the past the roadbed didn't be built as earth structure in new line, the disparity of the roadbed fill performance and the lowness of the compacting criterion, all that caused subgrade defect continuously. The roadbed condition was not only unimproved, even more deteriorate after the beginning of lift speed in 1994. The development of the high speed railway and railway for mixed passenger and freight traff make people wake up to high the subgrade compacting criterion. The harmony of it, the tracker superstructure, the tunnel and bridge structures is the one of the key problems in the railway modernization. To fit the transformation, it is necessary to put forward new subgrade design criterion and control the construction quality strictly.This paper through large quantity of the laboratory experiment and field test, analyzed the engineering meaning, applicability and their interdependence of compacting parameter used in domestic and international commonly. In this paper adopting soil physical property index match mechanics index to control the subgrade compacting quality, and it is more proper than the single index control in railway subgrade design criterion TB10001-99. From the total tendency, higher the compacting factor Kh is, better the strength, rigidity and water stabilization of the compacted soil. It is effect to control itself relative compaction. However some factors analyzed in this paper lead that between Kh and K30 , the one by one corresponding dependency relation not existence in existing filling classification. From the analysis of the discreteness and total tendency uniformity of compacting parameter and kinds of mechanics indexes, we propose that compacting factor in subgrade bed Kh>0.95, compacting factor in embankment filling Kh>0.90. Using air void to control compacting quality of fine grained soil abroad can control compacting factor and moisture content state and improve water stabilization at the same time. So we suggest defining in compacting construction 'fill compacted moisture content should be optimum moisture content (-3~+2)' to 'fill compacted moisture content should be less to optimum moisture content'.Absorbing the essence of the domestic and international experience, choose the suitable subgrade compacting parameter adapting to the railway line for mixed passenger and freight traff. Analyzing the measured dynamic stress attenuation in current subgrade and calculating the attenuation regular of the subgrade dynamic stress along with depth by program, to determine all parts dynamic stress and subgrade bed thickness. According to doubling elastic foundation theory to calculate the surface layer of subgrade bed thickness and bottom layer of subgrade compacting criterion. Strengthened the function of the subgrade bed, enforced the track foundation, reduced the maintenance and repair and eliminated the possibility of frost boiling from the construction. At the meantime regulate the subgrade bed should be special designing in Anti-freezing and waterproof aspects, and the drainage layer must be installed if the groundwater is abundant. Synthesizing the above factors put forward the subgrade compacting criterion scheme of railway line for mixed passenger and freight traff in speed per hour 140 kilometers and 160 kilometers.