Comparative Analysis On Mechanical Properties Of Different Types Of Subgrade For High-Speed Railway

Design of subgrade is very important in the whole process of high-speed railway design and the surface layer of subgrade is a main part in the subgrade structure. In current high-railway design code TB10020-2009, graded broken stone (GBS) is adopted as the material of the surface layer of subgrade. In order to improve the mechanical behavior of high-railway structure, this thesis introduces the bituminous stabilized macadam (BSM) and cement stabilized macadam (CSM) to the surface layer of subgrade in the high-railway structures. The surface layer of subgrade structure of different combinations are proposed and their behaviors are analyzed and compared.Types of high-railway subgrade structure and their material behavior are introduced in this thesis. The mechanical behaviors and economic application of BSM and CSM to road structure are summarized and their feasibility application to high-railway structure are verified. Therefore, two types of the surface layer of subgrade are proposed. Type Ⅰ is subgrade bed of BSM, which composed of BSM on the top10cm and GBS in the bottom30cm.; and type Ⅱ is subgrade bed of CSM which consists of CSM in the top20cm and GBS in the bottom20cm. The mechanical behavior of surface layer of BSM, CSM and GBS are compared and analyzed.In the static analysis, non-deformability and anti-crack resistance are analyzed. The displacement and principle tensile stress in the surface layer of subgrade, the bottom layer of subgrade, embankment and foundation are analyzed. Results showed that the displacement of CSM in the every layer is least, the displacement of BSM take the second place and that of GBS is the largest. In contrast, the analysis results of principle tensile stress indicate that the anti-crack resistance of BSM is better than CSM.Dynamic analysis is chosen to study key indexes of these three kinds of subgrades, including displacement, acceleration and stress. The comparison results show that analysis result of displacement is similar with that of static loads; acceleration of the subgrade bed with CSM is smaller than that of BSM and the acceleration of the subgrade bed with GBS is largest; the dynamic stress of the subgrade bed with CSM is smaller than that of BSM and they are much smaller than that of GBS. Trends of dynamic stress in different velocity are analyzed and results show that with the increase of velocity, stress does not increase linearly but gradually trends gently. Moreover, the rate of growth of CSM is least.