The effect of biopolymer treatment on the potential instability of a soft soil under cyclic loading

Mud pumping is frequently reported as a serious concern in soft soil foundations subjected to repeated train loads. Although conventional methods such as lime and cement treatment can be used to alleviate this problem, they can cause considerable environmental damage. This paper presents the novel use of an eco-friendly biopolymer, Xanthan Gum (XG), to enhance the performance of soft subgrade under cyclic loading in the context of railways. A series of cyclic triaxial tests were carried out on natural subgrade soil with a history of mud pumping and the results were compared with XG-treated specimens subjected to typical loading conditions representative of heavy-haul trains. The efficacy of XG was examined by varying cyclic stress ratio (CSR) and XG content for different test specimens. The results indicate that XG, with its hydrophilic nature and densification of soil specimens through the pore filling and particle bonding process, can help reduce the accumulated excess pore pressure (EPP) effectively, thereby substantially improving soil resistance to cyclic loading and mitigating the migration of pore water within the test specimen. The permanent strains are found to be less than 3% despite using a small amount of XG content (0.5%) under a high cyclic stress ratio (CSR = 0.8) and the number of loading cycles up to 50,000 cycles, while the resilient modulus of soil can increase significantly as XG content increases.