UNSATURATED SOILS

UNSATURATED SOILS MECHANICS AND REACTIVE CLAYS

Key Researchers: Olivier Buzzi, Stephen Fityus

PROBLEM DESCRIPTION

Unsaturated soils contain both air and fluid phases in their pores and the framework of unsaturated soil mechanics provides the theoretical and experimental foundations to analyse the behaviour (in terms of volume change, strength and water flow) of soils that are not saturated. A key difference with conventional soil mechanics is the existence of a negative pore water pressure referred to as suction, which soils can sustain, both in saturated and unsaturated domains. Adequately capturing the effect of suction on a soil behaviour is a complex task that is not commonly used in professional practice. Yet, transportation infrastructures (railway, roads, bridge abutments, etc..) and buildings are commonly constructed on unsaturated soils and also reactive soils. Such soils can exhibit large volume variations upon changes of suction and can exert significant swelling pressure on structures, which is problematic and needs to be accounted for in a design process. The aim of this research is to provide new knowledge on the behaviour of unsaturated soils and reactive clays. Advanced laboratory and field testing on soils are complemented by microstructural investigations in order to correlate macroscale observations to soil structure.

SCIENTIFIC AND ENGINEERING APPROACHES

  • Development of experimental techniques to impose and measure suction (high capacity tensiometers, osmotic method, vapour equilibrium) and measure volume change (HSP coating)
  • Characterisation of soil microstructural evolution upon loading (mechanical and hydric) via mercury porosimetry and microscopy imaging
  • Characterisation of volume change with suction (swelling, shrinkage, collapse) under different boundary conditions
  • Measurement of soil water retention curves and permeability functions of unsaturated soils and reactive clays
  • Measurement of strength and deformability in the unsaturated domain

APPLICATIONS

  • Effect of plant-induced suction on slope stability
  • Application of unsaturated soil mechanics to mine rehabilitation
  • Use of problematic soils in encapsulated road embankments
  • Effect of moisture content changes in reactive soils underlaying railway foundations
  • Foundation remediation in expansive soils using expanding polyurethane resin.
  • Effect of suction on the stability of coal stockpile

Figure 1