Chemical Injections Realized with Null Pressure for Underpinning the Foundation of an 18th Century Building Located in the Historical City of Cuenca (Spain)

Abstract

The injection of expanding polyurethane resin into the soil is a well-known technology, which every time more often is used in interventions for reinforcing shallow foundations. It is noteworthy that it is a non-destructive technology, which generated small disturbance in the structure, and that is why is very appreciate for sensitive buildings as those belonging to the country's architectural heritage.

Soil Injection Technology Using an Expandable Polyurethane Resin: A Review

“…The reaction time, which depends on the type of the injected resin and the catalysts used, is controlled by the admixed components temperature [79]. By regulating the mixing temperature, it is possible to control the reaction time, which has a significant role in the practical applications of the technology [67,80].…”

“…Although some conducted studies stated that the flow and propagation of the PU expandable foam are subjected to the cavity expansion theory when injected into the soil massive [77,78,80,93,94]. However, this theory is considered if the resin is injected at low injection pressure, leading to the resin expansion, not along the fracture but in the form of a ball or cylinder; consequently, it leads to high resin consumption and the inability to achieve a uniform distribution for the foundations lifting, and it turns out to be ineffective.…”

“…In gravels and sands, the propagation is mainly by impregnation of the intergranular spaces. On the other hand, in clays, the voids and fractures present in the soil's macrostructure are saturated by the resin or compressed by the swelling pressure during the expansion process [80].…”

“…The chemical reaction of the two components occurs instantly, causing the resin's expansion by increasing its volume. The chemical reaction begins and ends quickly, and the resin starts hardening in the soil massive within a few seconds (up to 30 s), changing from a liquid to a solid-state, and reaching its final physic-mechanical characteristics within a few minutes (15-30 min) [64,65,67,79,80]. The resin has an expansion pressure potential that can reach up to 10,000 kPa [64,67,69,78].…”

“…In practice, the reaction time depends on the particular resin and catalysts used for the chemical reaction; however, it is also influenced by the admixed temperature of the components. Therefore, controlling the temperature of the components during the injection process allows one to speed up or slow down the reaction time, controlling the speed of the hardening process [67,79,80]. The primary role of the injection pressure is to control the flow of the material, allowing the resin's propagation through the cracks made by the fracking process.…”