Abstract
Permeability, filtration and shearing strength were widely considered to be the key properties in evaluating the performance of railway subballast. An investigation on these key properties of railway subballast was presented in this paper. A constant head permeability test and a middle scale direct shear test of railway subballast were conducted in the research, aiming to investigate the subballast permeability and shear direct tests characteristics. Four different designed gradations within the standards were subjected to the investigation in order to study the particle size distribution effect on permeability performance of subballast. Lab results showed that drainage capacity and shearing strength of subballast highly correlated with each other. Subballast with more large-size particles and a low coefficient of uniformity were proved to acquire good drainage of water and strong resistance ability to shear.
Highlights
Railway subballast which serves between ballast layer and subgrade layer is composed of much finer particles than the upper ballast
Several constant head permeability tests were conducted for each grading after which the calculated hydraulic conductivities of the four kinds of subballast with equation (1) were plotted in Fig. (4) and indicated by different shapes and colors of points and lines
Lambe and Head indicated that these three kinds of gradations possess good drainage while sample D should only be classified as relative poor drainage which may due to the increasing percentage of fine particles in sample D [26, 27]
Summary
Railway subballast which serves between ballast layer and subgrade layer is composed of much finer particles than the upper ballast. The trapped fines in the void changed the porosity and grading of ballast and, as a result, reduced the drainage capability of subballast layer. To satisfy the drainage requirement of subballast, uniformly graded particles were usually applied in the construction, which may lead to a structurally instability and poor filtration due to the large void between particles. Results revealed that particle size distribution have a deep influence on the subballast performance which showed well-graded packs of ballast which have a high Cu usually have two problems which were size segregation and reduction of drainage [25]. Results revealed that particle size distribution have a deep influence on the performance of subballast and specimen with more fine particles showed good filtration while poor permeability and shearing strength. Permeability and resistance were correlated and both have a strong relation with particle size distribution
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
