Underpinning of shallow foundations by expansive polyurethane resin injections. Case study: Cardinal Diego de Espinosa Palace in Segovia (Spain)

Abstract

The injection of expansive polyurethane resin into the soil is a technology that is beginning to be used for underpinning shallow foundations. It is noteworthy that this technology has been used on buildings of great historical value which are part of the country's architectural heritage. This article describes the work done on the Cardinal Diego de Espinosa Palace which consisted of injecting expanding polyurethane resin into the soil at different depths (Uretek Deep Injections) in order to mitigate the differential settlements detected in the structure. This injection technology has proven to be more effective than the more convention methods used in the past which consisted of raising the foundation by building concrete shafts, which did not manage to mitigate the causes of the pathologies observed in the palace.Key words: Underpinning, Injection, Expansive Resins, Historical buildings. ResumenLa inyección en el terreno de resina de poliuretano expansivo es una tecnología que se está comenzando a utilizar en el recalce de las cimentaciones superficiales. En este sentido, resulta más enriquecedor llamar la atención sobre aquellas actuaciones realizadas que, por ser edificaciones con un valor histórico relevante, forman parte del patrimonio arquitectónico de un país. El presente artículo describe la actuación realizada en el edificio histórico del Palacio del Cardenal Diego de Espinosa, consistente en la inyección de resina de poliuretano expansivo en el terreno a diferentes profundidades (Uretek Deep Injections), encaminada a mitigar la presencia de asientos diferenciales detectados en su estructura. Esta tecnología de inyección ha mostrado ser más efectiva que las anteriores actuaciones de recalce convencionales realizadas, recrecidos de la cimentación mediante la construcción de pozos de hormigón, en las que no se consiguieron mitigar las causas de las patologías observadas en el palacio.

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

“…In traditional injection techniques, a mixture of water and cement with additives, or non-expanding resins, is generally used. The design objectives of these treatments are controlled by the nature and quantity of the components present in the mixture and the injection pressure, which determines the area of influence of the consolidation [14].…”

Soil Injection Technology Using an Expandable Polyurethane Resin: A Review

“…The technology is primarily based on injecting the soil massive up to the required treatment depth by two components of polyurethane solutions (a polyol and an isocyanate) that are mixed in a hydraulic system and pumped under a high pressure into the soil, using an injection pistol through a small pre-made hole in the foundation, the diameter of which ranges within (12-30 mm) [64,65,67,[70][71][72][77][78][79]. The mechanism of this technology differs from other techniques due to the natural chemical reaction of its components, which leads the resin to expand volumetrically within a specified expansion ratio.…”

“…The resin's mixture changes from a liquid to a solid and hardens rapidly (in a few seconds). 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].…”

“…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.…”