Tree induced soil suction and slope stability

This paper provides an investigation of moisture migration patterns in the vicinity of mature trees and soil slope stability. A numerical model is presented for unsaturated moisture flow incorporating a sink term to represent water uptake by a tree. The resulting variation in soil moisture content (or suction) is then included within an extended slope stability analysis that employs a method of estimating shear strength as a function of suction in addition to net mean stress. The moisture transfer equation is solved via application of a finite element method. The resulting water uptake predictions have been validated previously and were shown to be in reasonable agreement with field measured data. The current work provides an assessment of the importance of this aspect of the problem on slope stability. Results show that seasonal soil suctions generated by a tree can influence the facture of safety against soil slope failure in the order of 8%. The research provides a further contribution to the overall assessment of slope stability. It may be included in routine calculations where maintenance of rail/road embankments may involve alteration (or removal) of vegetation. It may also be applied to vegetated natural slopes subject to deforestation or development.