Characterization of the mechanical behavior of the fine soil of railway subgrade under heavy train loading

摘要

Evaluating the behavior of a railway subgrade, especially if it is constituted of fine-grained materials, requires considerationof the unsaturated aspect of their behavior and the characteristics of railway traffic. In this study, interest is focusedon the characterization of the mechanical behavior of subgrade soil on a cut section of a railway located in Gabon. Morespecifically in analyzing the effect of the increase in the axle load on the subgrade material by consolidated undrained (CU)triaxial tests on reconstituted soil specimens. The studied material is known as pelite or mud. The objective of this study isfirst to perform monotonic CU triaxial tests to determine the failure characteristics under fully and near saturated conditionand to analyze the effects of the saturation degree and void ratio on the soil strength. Cyclic CU triaxial tests were thenperformed to study the accumulation of the deformation within the studied material during cyclic loading. Monotonic CUtriaxial tests showed that in the near saturated condition, the subgrade material already exhibited much greater strength butin the fully saturated condition, its strength was strongly reduced. Its stress-deformation behavior can change from ductileto brittle between fully and near saturated condition. Cyclic CU triaxial tests showed that in the fully saturated condition,the accumulated permanent deformations due to the passage of the heaviest axle stabilize but remain quite large. However,in the near saturated condition, the accumulated deformations are reversible as the soil is denser.