The effects of drainage on the behaviour of railway track foundation materials during cyclic loading

Abstract

This paper presents the results of a series of hollow cylinder tests carried out to investigate the role of drainage conditions on the response of railway track foundation materials during cyclic loading. Three sand-clay mixes were tested. It was found that, below a certain cyclic shear stress threshold, and depending on the drainage conditions, changes in principal stress direction should not adversely affect the cyclic stability of a railway foundation. However, significant stiffness degradation and failure may occur if this cyclic shear stress threshold is exceeded. The cyclic shear stress threshold increased with moderate additions of clay per unit volume of sand, and reduced significantly when specimen drainage was prevented. For the materials tested, the cyclic shear stress threshold in free-to-drain conditions was generally similar to the cyclic shear stress in the soil immediately below a 0·3 m deep ballast bed, but comfortably greater than the cyclic stress at a depth of 1 m below the sleeper base. In undrained conditions, the cyclic shear stress threshold was generally similar to the cyclic shear stress at a depth of 1 m below the sleeper base. This has implications for the suitability of such materials for railway track foundations.

Behaviour of saturated railway track foundation materials during undrained cyclic loading

“…The loading frequency used in the tests was 0.0083Hz or approximately 30 cycles per hour, at which a consistent response of the test control software could be achieved. The in situ cyclic loading frequency associated with train passage will be much higher; however, the quasi-static soil response depends on the loading frequency in relation to the soil permeability and the drainage path length, as discussed by Mamou et al (2017). The essential point is that the rate of loading combined with the drainage conditions imposed in the current tests gave a substantially uniform pore pressure distribution within the specimen, representative of undrained conditions in the field.…”

“…Materials B and C (Mamou et al, 2017). Below the cyclic stress threshold increasing magnitudes of cyclic shear stress had little or no effect on the resilient modulus, which for a given material remained broadly similar (85, 105 and 100 MPa for Materials B, C and D respectively) with less than 20% variation between the different material types.…”

“…The results suggest that the cyclic shear stress threshold for the development of significant permanent strains is affected by moderate additions of clay, up to about 14% (by dry weight) (Mamou et al, 2017).…”

“…The current paper aims to address this knowledge gap by investigating the influence of cyclic shear stress changes on the axial strain, pore pressure, resilient stiffness and susceptibility to failure of a range of soils used in railway track foundations. It draws on laboratory test data from materials having clay contents of 7-14% (Materials A to C) previously reported by Mamou et al (2017), as well as data on a material having a clay content of 24% (Material D), and discusses the generation of excess pore water pressures in undrained conditions in more detail.…”

Evolution of Longitudinal Resistance Performance of Granular Ballast Track with Durable Dynamic Reciprocated Changes

“…Tutumluer et al constructed ballast layers to investigate the ballast compaction, strength, and stability conditions before and after tamping [1]. Hollow cylinder tests were conducted to investigate the role of drainage conditions on the response of railway track foundation materials during cyclic loading [21].…”