Foundation Remediation using Expansive Polyurethane Resin
1: Injection of Expansive Polyurethane Resin to remediate cracks in a structure.|
Figure 2: Expansive Polyurethane Resin structure.
Figure 3: Interaction of two shots of resin in a 20 mm width crack. First shot is cracked by the second one. Macrovoids are visible.
Injection of expansive polyurethane resin is a common underpinning solution for individual houses, buildings and paving slabs. The pressure exerted during the chemical reaction producing the resin lifts the structure. When injected in expansive soils, which are very sensitive to water content changes, it is of particular importance to understand how soil-resin composite material behaves and how the resin may affect the soil's hydraulic properties and its swelling behaviour.
Indeed, desiccation cracks created during the soil shrinkage are filled with resin, meaning that any future wetting of the soil would lead to enhanced swelling that may over-lift the remediate foundation.
The Polyurethane Resin
Exothermic reaction between a polyol and isocyanate
Resin formation in the ground
Permeability of the resin
Permeability of the soil mass
Figure 4: Permeability of the resin as a function of its density
Figure 5: Experimental set up for in situ air permeability tests.
Figure 6: Evolution "flow rate-pressure" for both injected and non injected zones at different depths.
Figure 7: In situ monitoring of ground movement of injected and non injected zones
|Figure 8: Laboratory swelling tests on large injected and non-injected specimens did not show that injected specimens swell more|