Study On Centrifugal Model Teest Of Pile-Plank Subgrade And Column-Net Subgrade For Ballastless Track

It is certain that ballastless track will be the trend of research and development of passenger-dedicated line because of its being more smooth and less in need of maintenance. Pile-plank subgrade and column-net subgrade are two new types of subgrade in order to meet strict settlement requirements of ballastless track, so the research of whose engineering characteristics is of great significance. The preliminay design theory, settlement and pile-soil interaction characteristics of the two types of subgrade are investigated through centrifugal model test.It is shown that: The settlement of pile-plank subgrade is completed after pile-plank subgrade's being laid within five months; the settlement is completed when being in used for twelve months, and the settlement is 10.96mm; the pile of the structure is rock-socketed bored cast-in-place frictional pile with high potentials of bearing capacities whose diameter is small in proportion to its length.The comparative analysis of two groups of column-net subgrade centrifugal model test due to different pile spacings, 2m and 3m, is carried out. The settlement of which is 12.5mm and 21.0mm respectively, the former accounts for 59.5% of the latter; the pile-top load of the former and the difference between pile-top load in the center and in the edge of the former is comparatively minor; the reinforcement effect of the structure with 2m's pile spacing is better, which is beneficial for the smooth of ballastless track; the scheme with pile spacing of 2m is a more reasonable one; the varying characteristics of bearing capacity with time coincides with that of settlement with time; the pile of the structure is frictional pile socketed in rock with high potentials of bearing capacities; the settlement of the bottom suiface of upper part of subgrade mainly comprises the consolidation in the pile-reinforcement section, and the consolidation happens mainly caused by the penetration of piles into the geogrid reinforcement cushion.The comparative analysis between the design theory and the result of centrifugal test of the two types of subgrade shows: bearing capacity designs of the two are both conservative, so there is high potential of bearing capacity in either one; the settlement of either is able to meet the requirement of ballasted track; the result of tests validate the accuracy of the design theory based on controlling settlement as the dominant factor...