Static and Cyclic Triaxial Testing of Ballast and Subballast

Abstract

This paper discusses the triaxial testing of a ballast material and a subballast material, which are noncohesive, granular materials typically used for construction of a railway track substructure. Both static and cyclic triaxial tests were conducted. The cyclic triaxial tests simulated the behavior of these railway substructure materials under a large number of passing train wheels. The purpose of the static tests was to a priori identify the maximum stress level that could be applied in the cyclic tests, and to assess the strength and stiffness increase produced during the cyclic loading process. In order to accurately monitor the circumferential displacement during the static and cyclic tests, a new measuring device was developed. The experimental setup, the test procedure, and the test results are treated for the ballast and subballast materials. It is found that under cyclic loading the granular materials reveal a strong tendency to compact, even if the applied stress level is close to the static failure strength of the material. This compaction behavior generally causes a (significant) increase of the material strength and stiffness.