Climate-induced shrinking and swelling of clayey ground, causing building damage due to shallow foundation subsidence, is one of the most damaging geohazards in Britain today, costing the economy an estimated £3 billion over the past decade. This economic loss is expected to increase by 3-4 times by 2070 (BGS, 2021). In France, the most recent drought in 2022 has caused building damage for a cost estimated between 1.9 and 2.8 billion Euros (LeMonde, 2022). 

Current adaptation measures are designed following a ‘structural’ strategy, which means the soil must be ‘reinforced’ to minimise shrinkage-induced deformations. These include underpinning of foundations using micropiles, jet grouting, and expansive resin injection. However, these measures are invasive and associated with high economical and carbon cost. This ‘structural’ approach ignores that the shrinkage-induced foundation subsidence is generated by the climatic loading associated with evapotranspiration and that subsidence hazard can therefore be mitigated by attenuating such a loading. 

The geotechnical perspective 

Dry periods generate suction (negative pore-water pressure) at the ground surface that propagates downward. This process is reversed when a wet period follows. The zone where suction ordinarily fluctuates upon dry/wet periods is named ‘active’ and its depth is generally relatively stable. The increase and decrease of suction in the active zone typically cause little clay deformation because the clay is over-consolidated in the active zone having experienced the highest suction ever several times in the past. 

Exceptional droughts generate a first-time downward penetration of the suction into normally consolidated clay layers beneath the active zone that have never experienced an increase in suction in the past. This causes substantial deformation of the clay and subsidence of the peripheral foundation pads, in turn causing differential deformations with respect to the inner pads where evapotranspiration does not occur (umbrella effect).

Drought-induced clay deformation can be minimised by hindering the increase of suction underneath the foundation level. In turn, this can be achieved by either hindering the water flow taking place upward from underneath the foundation level or ‘refill’ the ground with the water lost by evapotranspiration. 

Research project

We will explore, experimentally and numerically, innovative concepts based on the use of capillary barriers and/or water sinks. They have the potential to revolutionise the market of engineering solutions due to their low cost, low carbon footprint, and sustainability associated with the possible reuse of demolition waste.