Subgrade reinforcement of old railway tracks using short soil–binder columns – Laboratory studies and field tests

Abstract

The subgrade of old railway tracks often exhibits poor geotechnical behaviour, particularly regarding the soils on which the ballast layer rests. Such poor behaviour implies significant maintenance costs and possession times. The reinforcement of subgrade soils by injection of binders may mitigate these malfunctions, but previous applications showed some limitations, and the quality of the results depends on many factors. Herein, the authors present some studies on the development of a subgrade reinforcement method, which minimises the impact on train operation, by using short soil–binder columns, formed with grouts injected into the subgrade by drilling through the ballast layer. Laboratory studies were performed to determine the strength and deformability of the mixtures of a clay soil with lime or cement. To assess the improvement of the geotechnical characteristics of that soil and to determine the permanent deformation of the track structure under cyclic loading, tests were performed on full-scale physical models. A reduction of about 60–80% was observed in settlement amplitudes of the reinforced physical models under cyclic loading. Lastly, the reinforcement method was employed on a track in operation that exhibited a poor behaviour, the subsequent geotechnical improvements were assessed and the dynamic responses of the track before and after grouting were compared. After the treatment, a general reduction of about 15–20% was observed in peak vertical accelerations measured on the sleepers. The results suggest that, from both the technical and the economic viewpoints, the proposed reinforcement method is a valid alternative for rehabilitating railway platforms, notably in old single-track lines.