Influence of osmotic suction on the shear strength of root-permeated soil

Most civil infrastructure is built on and remain under unsaturated conditions for most of its service life, so the longevity of those structures depends on the actual strength or bearing capacity of the subgrade soil. Incorporating unsaturated soil mechanics into construction practices has become challenging due to lack of understanding, especially of the mostly saline soils prevalent along the coastal belt of Australia. Omitting the benefits of salinity based osmotic suction and the influence of tree roots can lead to undue design conservatism. Previous studies have proven that the matric suction and root reinforcement influence the shear strength of natural or compacted soil, however the number of studies that focussed on the role of osmotic suction with or without the influence of tree roots are limited. The concept of green corridor or the use of native vegetation in the railway industry has become more popular over the past few decades because they are sustainable, environmentally friendly, cost-effective, long-lasting, and provide wind protection and noise barriers. Most importantly, tree roots can significantly increase the shear strength of soil because of the additional matric suction induced by root water uptake, and root reinforcement. However, the contribution that tree roots has on the shear strength of soil under coastal environmental conditions (or with osmotic suction) is yet to be investigated and discussed comprehensively.