Improvement of existing railway subgrade by deep mixing

Abstract

Many old railway lines in Europe need to be reinforced as they no longer meet the requirements of modern traffic. This paper presents the results of field tests carried out, as part of the French RUFEX research project (Reinforcement of railway tracks), to study the feasibility of the installation of 600 mm diameter vertical soil-cement columns under existing railway lines without removing the tracks or cementing the ballast. These columns were installed under an execution procedure is described and the quality/homogeneity of the mixed material is studied with excavated columns after curing periods of 28 and 180 days and several samples were taken for laboratory testing. The tests included unconfined compressive strength tests, splitting tensile strength tests, porosity and ultrasonic wave velocity measurements. The results show an increase in strength of 30% between 28 and 180 days. A linear correlation between compressive and tensile strengths is proposed. Besides, data obtained from ultrasonic wave velocity measurements suggests that this test can be used for the estimation of index parameters such as density and porosity but also for preliminary assessments of static stiffness and strength by correlation with the dynamic elastic modulus.

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Acknowledgements

The authors would like to thank Soletanche-Bachy and SNCF for their strong participation in the project and in the field works.