Bioremediation of Soft Subgrade for Enhanced Performance of Rail Infrastructure
- Publication Type:
- Thesis
- Issue Date:
- 2024
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| Filename | Description | Size | |||
|---|---|---|---|---|---|
| thesis.pdf | 18.97 MB |
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Recent years have seen an increased demand for faster and heavier rail transportation due to the growing population and industrialisation, which means a surge in axle loads (up to 35-40 tonnes) and train speeds (up to 250kmph). The existing tracks constructed over the soft soils along in the coastal Australia often demand frequent maintenance owing to the low bearing capacity of the subgrade susceptible to instability under unfavourable loading and drainage conditions. Despite numerous solutions available, such as geosynthetics inclusions and chemical stabilisation methods, a sustainable solution for remediation of subgrade soil instability has not been established. Although the use of biopolymers to stabilise soil has recently emerged as an eco-friendly and cost-effective approach, its application to rail track foundations has not been investigated.
In this research work, a series of laboratory experiments were carried out to examine the capabilities of a specific biopolymer, Xanthan Gum (XG), to stabilise low plastic soil under railway loading conditions. The soil was obtained from the real field during the track maintenance and had a history of mud pumping. Specifically, the study aims to investigate (i) the influence of fines, and XG contents on strength, stiffness, followed by the optimum biopolymer content, (ii) the effect of XG on critical state characteristics and undrained response system (iii) the occurrence of subgrade fluidisation and effect of XG on altering internal instability of soil and mitigating the fluidisation, (iv) the combined effect of loading parameters (frequency and CSR) and XG content on the undrained cyclic response of treated soils.
The results indicated that the optimum XG content should be within the range of 1.5-2.0% by weight of soil, and increasing fines content resulted in significant stiffness and strength increase of soil. Besides, XG enhanced the residual strength and reduced the softening behaviour. The tests on cyclic response under railway loading revealed that XG mitigated the internal migration of moisture, thereby preventing fines from pumping towards the upper layers. The induced plastic strains and excess pore pressure were significantly less than the untreated soils, which confirmed the excellent resistance of the XG-treated soil against cyclic loading without losing stiffness. XG soil treatment provides apparent cohesive strength in low-plastic soil by forming interparticle bridging, thus effectively reducing the fluidisation potential under cyclic excitation.
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