Access the full text.
Sign up today, get DeepDyve free for 14 days.
References for this paper are not available at this time. We will be adding them shortly, thank you for your patience.
applied sciences Article Chemical Injections Realized with Null Pressure for Underpinning the Foundation of an 18th Century Building Located in the Historical City of Cuenca (Spain) José Ramón Sánchez Lavín *, Félix Escolano Sánchez and Alberto Mazariegos de la Serna Civil Engineering Department: Construction, Infrastructures and Transportation, Technical University of Madrid (UPM), Alfonso XII 3, 28014 Madrid, Spain; felix.escolano@upm.es (F.E.S.); alberto.mazariegos@upm.es (A.M.d.l.S.) * Correspondence: joseramon.sanchez@upm.es; Tel.: +34-910-674-614 Received: 6 June 2018; Accepted: 5 July 2018; Published: 11 July 2018 Featured Application: 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. Abstract: Chemical injection of expansive polyurethane resin in the ground is a well-known technology that is also used for underpinning shallow foundations. It is noteworthy that it has been recently used with success on buildings of great historic value that are part of the country’s architectural heritage. This article describes the work undertaken on a historic building located in the city of Cuenca (Spain), for improving ground condition through injecting below foundation, in order to stop the differential settlements detected in the structure. This technology has proven to be, at least, as effective as the more conventional methods used in the past as supporting the foundation by concrete shafts or micropiles. Keywords: underpinning; chemical injection; expansive resins; heritage; historical buildings 1. Introduction Architects and engineers working in ancient cities very often have to deal with situations in which historic buildings and alike are affected by pathologies related with ground conditions. Eventually, if soil is not improved, the pathologies can progress to the point where the conservation of these cultural assets may be jeopardized. In most cases, due to their age, these structures are on well-consolidated foundations, but its strength properties become degraded by man-made activities [1]. The soil supporting the foundation changes over time and this produces additional stress on the foundation causing deformations that are very different than the ones that prevailed during many years. Sometimes, intervention to change the use of the building gives way to a new distribution of loads which generates differential settlements, but other times, degradation of soil conditions is the main cause. Changes in the mechanical properties of the soil supporting the foundation may be caused by: - Leaks or cracks in water pipes change the soil moisture content. - Fluctuations in the water table in the area. Appl. Sci. 2018, 8, 1117; doi:10.3390/app8071117 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 1117 2 of 11 - Biological activity as growth and rotting of roots. - Physical and chemical degradation of buried foundation materials. Soil improvement is the first step to start repairing these pathologies [2]. This can be achieved by many ways, but now it is available a non-destructible low-disturbing technology that consist of injecting expanding polyurethane resin. This technology and its recent application to historic buildings are described in this article. 2. General Description of the Technology Traditional injection techniques use a mixture of water and cement with additives. They are non-expanding resins. Soil improvement is achieved by applying pressure to the grout when liquid, and void reduction or consolidation is achieved by the volume eventually occupied by the injected grout. Injecting expanding polyurethane resins is different due to the chemical nature of its components: polyurethanes. In fact, they require no injection pressure. The solidified resin achieves a natural balance with the surrounding soil when the swelling pressure of the resin as a result of the reaction coincides with the average confining pressure of the soil. This way, the mechanical properties of the ground can be improved. 2.1. Basic Concepts of Expanding Polyurethane Resin Expanding polyurethane resins are produced by the exothermic reaction between a polyol and an isocyanate when combined in volumetrically established proportions. During the chemical reaction, a large amount of carbon dioxide is produced which causes the volumetric expansion of the mixture and formation of a spongy structure where the gas bubbles are trapped. The production of carbon dioxide requires the presence of water which reacts with isocyanate group. In the absence of water, a chemically inert swelling agent with a low boiling point is used, which is vaporized consuming part of the polymerization heat. The mixture changes from a liquid to a solid and hardens in a very short time. The reaction time, which depends on the particular resin and catalysts used, is influenced by the temperature of the admixed components. By controlling the temperature of the components, it is therefore possible to speed up or slow down the reaction time. The pressure exerted during the swelling and the final position of the resin depends on the expansion capabilities of the gas in the bubbles before it hardens. The “closed cell” structure of the expanded resin is shown in Figure 1. The images were obtained using an electron microscope [3] and show the microscopic structure of the Geoplus resin used by Uretek [4] under free swell conditions 3 3 corresponding to a density equal to 37 kg/m . The density of the liquid mixture is equal to 1070 kg/m , very close to that of water. Under these conditions, the expanding volume is equal to 30 times the original volume of the mixture [5,6]. The mechanical properties of the resins can be found in the studies conducted by accredited European laboratories. Of particular note is the fact that the mechanical resistance of the expanded and hardened resin depends on the degree of expansion [6]. For specific gravity between 0.5 and 3.3 kN/m , the resistance values are between 0.2 and 6.0 MPa. The elastic modulus of the resin is comparable to that of any type of soil where a foundation is built. It can vary between 10 and 80 MPa depending on the density obtained after polymerization of the resin. These values are comparable to the modulus of average elasticity of soils that have been obtained from the bibliographic references of the main Spanish authors [7,8], Table 1. Consistent with the above, it can be concluded that after injecting expanding polyurethane resin the volume of treated soil does not modify the rigidity or distribution of force under the treated area [9]. In other words, there is no creation of “hard points” in the soil and the procedure for injecting resin can be considered suitable for partial or localized treatment [10]. Appl. Sci. 2018, 8, 1117 3 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 11 Figure 1. Images obtained with the electron microscope of the Geoplus expanding polyurethane resin Figure 1. Images obtained with the electron microscope of the Geoplus expanding polyurethane without confinement (density equal to 37 kg/m ). (a) Enlarged 100; (b) Enlarged 200. resin without confinement (density equal to 37 kg/m ). (a) Enlarged × 100; (b) Enlarged × 200. Table 1. Elastic modulus in different types of soil. Table 1. Elastic modulus in different types of soil. Soil Type Elastic Modulus (MPa) Elastic Modulus of Resin (MPa) Soil Type Elastic Modulus (MPa) Elastic Modulus of Resin (MPa) Sand 10 to 25 Sand 10 to 25 Medium sand compactness 15 to 30 Medium sand compactness 15 to 30 Dense sand compactness 35 to 55 Dense sand compactness 35 to 55 10 to 80 10 to 80 Sand and gravel 70 to 180 Sand and gravel 70 to 180 Medium consistency clay 5 to 10 Medium consistency clay 5 to 10 Hard clay 10 to 25 Hard clay 10 to 25 2.2. Injection Technology 2.2. Injection Technology Injection technology allows you to inject polyurethane resin into the soil at different depths Injection technology allows you to inject polyurethane resin into the soil at different depths through small perforations, causing minimal disturbance to structures and the overlying ground in through small perforations, causing minimal disturbance to structures and the overlying ground in order to solve problems related to the capacity of the ground under foundations. The treated soil is order to solve problems related to the capacity of the ground under foundations. The treated soil is consolidated in a vertical or sub-vertical direction thanks to a succession of low pressure injections of consolidated in a vertical or sub‐vertical direction thanks to a succession of low pressure injections of the resin under the foundation. Once the resin injected into the soil expands, the soil interface can be the resin under the foundation. Once the resin injected into the soil expands, the soil interface can be re-established at different depths and in areas where the admissible stress values are low (see Figure 2). re‐established at different depths and in areas where the admissible stress values are low (see Figure A better load distribution is thus achieved and the tension peaks under the foundation are limited. 2). A better load distribution is thus achieved and the tension peaks under the foundation are limited. Appl. Sci. 2018, 8, 1117 4 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 4 of 11 Figure 2. Tension status under the foundation after treatment. Figure 2. Tension status under the foundation after treatment. 2.3. Injection Methodology 2.3. Injection Methodology The methodology and method procedure are based on drilling holes less than 30 mm (typically The methodology and method procedure are based on drilling holes less than 30 mm (typically between 12 and 26 mm), spaced between 50 and 150 cm apart. Figure 3a. Metal pipes are then between 12 and 26 mm), spaced between 50 and 150 cm apart. Figure 3a. Metal pipes are then inserted inserted into these holes down to the established depths, Figure 3b, and the expanding resin is into these holes down to the established depths, Figure 3b, and the expanding resin is injected into the injected into the soil through the pipes. The injection is controlled following specific protocol. The soil through the pipes. The injection is controlled following specific protocol. The two basic points of two basic points of this injection protocol include the injection head of the resin, Figure 3c and the this injection protocol include the injection head of the resin, Figure 3c and the laser level that controls laser level that controls the lifting of the structure, Figure 3d. the lifting of the structure, Figure 3d. The resin is injected into the soil in a liquid state [11]. Almost instantly, a chemical reaction is The resin is injected into the soil in a liquid state [11]. Almost instantly, a chemical reaction triggered causing an increase in volume and the resin changes from a liquid to solid state. The is triggered causing an increase in volume and the resin changes from a liquid to solid state. expansion pressure of the resin can reach 10.000 KPa. The reaction begins and ends very quickly. The The expansion pressure of the resin can reach 10.000 KPa. The reaction begins and ends very quickly. resin reaches its final physical‐chemical characteristics in a few seconds. The resin reaches its final physical-chemical characteristics in a few seconds. When the resin penetrates the soil to be treated and increases in volume, it compresses the soil When the resin penetrates the soil to be treated and increases in volume, it compresses the soil in in all directions. This radial expansion is favored by the pathways that offer the least resistance. The all directions. This radial expansion is favored by the pathways that offer the least resistance. The resin resin continues to expand until the soil prevents any further radial compression. At that point, the continues to expand until the soil prevents any further radial compression. At that point, the only only possibility for expansion is an upward displacement of the soil [12]. possibility for expansion is an upward displacement of the soil [12]. When this initial lifting is observed, it means that the consolidating action is being directed When this initial lifting is observed, it means that the consolidating action is being directed vertically upward and that this is the direction that offers the least resistance, while the surrounding vertically upward and that this is the direction that offers the least resistance, while the surrounding soil offers greater resistance in respect of the decrease in the structural load, which means that the soil offers greater resistance in respect of the decrease in the structural load, which means that the foundation soil has been compacted enough to withstand not only the increase in static loads, but also the loads created by the lifting [5,6]. Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 of 11 This initial rising of the structure (tenths of mm), is what makes it possible to confirm the effectiveness of the method in real time. When the resin is injected at different depths, the injection usually begins with the top level, proceeding to the next level once the resin mixture hardens. Appl. Sci. 2018, 8, 1117 5 of 11 During the injection, the amount of mixture used is measures at each injection point and compared with the nominal consumption for the project. After the injection, a laser level is used to foundation soil has been compacted enough to withstand not only the increase in static loads, but also detect any vertical movement of the treated structure. This is the only way to check the effectiveness the loads created by the lifting [5,6]. of soil treatment in real time. Figure 3. Stages of the process: (a) Drilling, (b) Introduction of the injection pipes, (c) resin injection Figure 3. Stages of the process: (a) Drilling, (b) Introduction of the injection pipes, (c) resin injection head, (d) laser level to control lifting. head, (d) laser level to control lifting. 3. Historical Setting of the City of Cuenca and the Building under Study This initial rising of the structure (tenths of mm), is what makes it possible to confirm the Founded by the Romans more than 2000 years ago, Cuenca is one of the most ancient cities on effectiveness of the method in real time. When the resin is injected at different depths, the injection the Iberian Peninsula. The City was declared a World Heritage Site by The United Nations usually begins with the top level, proceeding to the next level once the resin mixture hardens. Educational, Scientific and Cultural Organization in 1996 because of its magnificently conserved During the injection, the amount of mixture used is measures at each injection point and compared original urban landscape: a medieval fortress, civil and religious monument from the 12th to 18th with the nominal consumption for the project. After the injection, a laser level is used to detect any centuries and the exceptional blending of the city with the breath‐taking natural environment. vertical movement of the treated structure. This is the only way to check the effectiveness of soil The city is enclosed by a wall of Arabic origin, part of which has been conserved, along with an treatment in real time. entrance. Cuenca’s historical monuments include the remains of a Castle (12th century), the Arabic 3. Mang Historical ana Tower, t Setting he C ofa the thedra City l (of 12t Cuenca h to 18th cent and the urBuilding ies) the Convent of under Study the Salves (16th century), the Hanging Houses (11th to 15th centuries) and St. Paul’s Bridge (16th to 20th centuries). Founded by the Romans more than 2000 years ago, Cuenca is one of the most ancient cities on the During the urbanistic and architectural splendor of the Late Middle Ages (11th to 15th Iberian Peninsula. The City was declared a World Heritage Site by The United Nations Educational, centuries), Cuenca rose up as a powerful industrial city which experienced notable economic success Scientific and Cultural Organization in 1996 because of its magnificently conserved original urban thanks primarily to its textile and livestock industries. The cloth trade and rug production brought landscape: a medieval fortress, civil and religious monument from the 12th to 18th centuries and the with them an extensive transformation industry that included laundering, dry cleaning and exceptional blending of the city with the breath-taking natural environment. weaving. During the 19th century the city withstood a relevant growth. At that time, Rey‐Alfonso The city is enclosed by a wall of Arabic origin, part of which has been conserved, along with an VIII Street was the main thoroughfare connecting the new neighborhoods to the Plaza Mayor. entrance. Cuenca’s historical monuments include the remains of a Castle (12th century), the Arabic In modern days, the city still enjoys a great activity as an important economic and cultural Mangana Tower, the Cathedral (12th to 18th centuries) the Convent of the Salves (16th century), center. The city combines modernity with the old flavor of its entire history, and their citizen are the Hanging Houses (11th to 15th centuries) and St. Paul’s Bridge (16th to 20th centuries). proud and compromise with keeping the old buildings as part of their heritage. During the urbanistic and architectural splendor of the Late Middle Ages (11th to 15th centuries), Cuenca rose up as a powerful industrial city which experienced notable economic success thanks primarily to its textile and livestock industries. The cloth trade and rug production brought with them an extensive transformation industry that included laundering, dry cleaning and weaving. During the 19th century the city withstood a relevant growth. At that time, Rey-Alfonso VIII Street was the main thoroughfare connecting the new neighborhoods to the Plaza Mayor. Appl. Sci. 2018, 8, 1117 6 of 11 In modern days, the city still enjoys a great activity as an important economic and cultural center. The city combines modernity with the old flavor of its entire history, and their citizen are proud and compromise with keeping the old buildings as part of their heritage. Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 11 3.1. Building Features 3.1. Building Features The building that was repaired stands at the top of the city’s historic quarter, specifically at Street The building that was repaired stands at the top of the city’s historic quarter, specifically at Sánchez Vera n 11. The building is over 130 years old. It is a four-level construction with no basement Street Sánchez Vera nº 11. The building is over 130 years old. It is a four‐level construction with no (Figure 4). It is a wooden structure with reddish-hued solid brick facing. basement (Figure 4). It is a wooden structure with reddish‐hued solid brick facing. Figure 4. Panoramic view of the historical building. Figure 4. Panoramic view of the historical building. 3.2. Pathologies Observed 3.2. Pathologies Observed The pathologies were caused mainly by differential settlement, which were compromising the The pathologies were caused mainly by differential settlement, which were compromising the preservation of the entire structure [13]. According to the available information, the settlement was preservation of the entire structure [13]. According to the available information, the settlement was caused by successive breakdowns in the sewer system the previous years, with water changing the caused by successive breakdowns in the sewer system the previous years, with water changing the moisture content of soils at building’s foundation. moisture content of soils at building’s foundation. In this case, the foundation reinforcement was aimed at improving soil density in order to stop In this case, the foundation reinforcement was aimed at improving soil density in order to stop movement and to recover bearing capacity, prior to begin the planned renovation of the entire movement and to recover bearing capacity, prior to begin the planned renovation of the entire building. building. 4. Design and Dimensioning of the Intervention 4. Design and Dimensioning of the Intervention Site investigation showed that the building foundation consists of a spread footing made of Site investigation showed that the building foundation consists of a spread footing made of bonded stone masonry. The depth of the foundation was about 1.0 m. The footing was embedded on bonded stone masonry. The depth of the foundation was about 1.0 m. The footing was embedded on a man-made fill layer. The total thickness of this layer was 1.7 m, so foundation was bearing on this a man‐made fill layer. The total thickness of this layer was 1.7 m, so foundation was bearing on this low-strength poor-quality layer, with values of N (Dynamic Probing Medium) between 1 and 30. low‐strength poor‐quality layer, with values of N10 (Dynamic Probing Medium) between 1 and 30. Underneath, just below the man-made fill, there was the untouched soil, that consists of hard Underneath, just below the man‐made fill, there was the untouched soil, that consists of hard marly-clay layer. This layer extended belong the stress bulb of the foundation. marly‐clay layer. This layer extended belong the stress bulb of the foundation. This layer distribution, where an impervious clay layer is below a more permeable layer, This layer distribution, where an impervious clay layer is below a more permeable layer, facilitates water to keep retaining on the upper man-made fill and stay there for long period of facilitates water to keep retaining on the upper man‐made fill and stay there for long period of time, time, giving place to soften and even collapse by degradation of local areas. giving place to soften and even collapse by degradation of local areas. The collapse of those areas generates differential settlement in the buildings, follows by cracks The collapse of those areas generates differential settlement in the buildings, follows by cracks and fissures at a 45º angle to the ground, with a stepped course typical of brick masonry. and fissures at a 45º angle to the ground, with a stepped course typical of brick masonry. Zones to be treated by resin injection are usually chosen based on the location of the damage; however, in this case, as the pathologies were all over the building, the entire foundation was treated. Nevertheless, resin admission is a quantitative index of the soil conditions at each point. The treatment should be limited to the area of influence of the foundation (Boussinescq bulb) or to a certain “level” to be determined based on the available geotechnical information. Based on these Appl. Sci. 2018, 8, 1117 7 of 11 Zones to be treated by resin injection are usually chosen based on the location of the damage; however, in this case, as the pathologies were all over the building, the entire foundation was treated. Nevertheless, resin admission is a quantitative index of the soil conditions at each point. The treatment should be limited to the area of influence of the foundation (Boussinescq bulb) or Appl. Sci. 2018, 8, x FOR PEER REVIEW 7 of 11 to a certain “level” to be determined based on the available geotechnical information. Based on these conditioning factors, the treatment area for this building was limited to a depth of 3.0 m below the conditioning factors, the treatment area for this building was limited to a depth of 3.0 m below the street level, that means 2.0 m below footing bearing surface. (Figure 5). street level, that means 2.0 m below footing bearing surface. (Figure 5). Figure 5. Image of the part of the building that was treated and details of the location of the injection Figure 5. Image of the part of the building that was treated and details of the location of the tubes. injection tubes. The intervention was divided into two phases: The intervention was divided into two phases: • Phase I. Surface compaction. Injecting the first meter below street, around the spread footing in Phase I. Surface compaction. Injecting the first meter below street, around the spread footing in order to improve the geomechanical characteristics of the foundation, and filling the gaps order to improve the geomechanical characteristics of the foundation, and filling the gaps between between the foundation and the soil. the foundation and the soil. • Phase II. Deep consolidation. Injections performed at different depths (3 levels) into the soil Phase II. Deep consolidation. Injections performed at different depths (3 levels) into the soil affected by the building loads. affected by the building loads. The number of injection levels is based on the depth of the degraded soil defined by the site The number of injection levels is based on the depth of the degraded soil defined by the site investigation. As a starting point, the concept of pressure bulb for shallow foundation may be investigation. As a starting point, the concept of pressure bulb for shallow foundation may be considered. Injection levels are usually separate between 0.5 and 1.0 m, Figure 6. considered. Injection levels are usually separate between 0.5 and 1.0 m, Figure 6. If several injections are made very close to each other along a vertical line, which is what we If several injections are made very close to each other along a vertical line, which is what we want want to show in Figures 2 and 6, it will happen that in the first part of the expansion process, when to show in Figures 2 and 6, it will happen that in the first part of the expansion process, when the the internal pressure increases and the ground responds elastically, later it will begin a plastic internal pressure increases and the ground responds elastically, later it will begin a plastic deformation deformation until reaching the limit of the internal pressure. It is evident that when this pressure until reaching the limit of the internal pressure. It is evident that when this pressure limit is reached, limit is reached, the resin will solidify. This process is almost immediate and its duration is several the resin will solidify. This process is almost immediate and its duration is several seconds. seconds. Appl. Sci. 2018, 8, 1117 8 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 11 Figure 6. Treatment levels along the building’s foundation walls. Figure 6. Treatment levels along the building’s foundation walls. 5. Foundation Underpinning Using Resin Injection 5. Foundation Underpinning Using Resin Injection The underpinning of the foundation was performed by injecting expanding polyurethane resin. The The res underpinning in injection phas of the es foundation included in twas he prot performed ocol: by injecting expanding polyurethane resin. The resin injection phases included in the protocol: • Drilling and installation of injection pipes. • Injection of the resin. Drilling and installation of injection pipes. • Instrumentation and control of the injection. Injection of the resin. Instrumentation and control of the injection. 5.1. Drilling and Installation of Injection Pipes Small electric rotary drillers are used to make the holes for the installation of the injection pipes 5.1. Drilling and Installation of Injection Pipes through the foundation (see Figure 3). This drilling system does not transmit vibrations to the structure. The perforations are 26 mm in diameter and were made with screw augers of different Small electric rotary drillers are used to make the holes for the installation of the injection pipes lengths to reach the exact depth. For this case the injection levels were 2.00, 2.40 and 3.00 m. The through the foundation (see Figure 3). This drilling system does not transmit vibrations to the structure. perforations were separated horizontally 1.50 m. The perforations are 26 mm in diameter and were made with screw augers of different lengths to reach Once the foundation is pierced, metallic 12 mm diameter pipes were installed by vibration. the exact depth. For this case the injection levels were 2.00, 2.40 and 3.00 m. The perforations were These pipes are afterwards used for injection so they are equipped with close valves at the toe to separated horizontally 1.50 m. prevent the obstruction of the pipe as it is being installed in the soil. The length of the injection pipes Once the foundation is pierced, metallic 12 mm diameter pipes were installed by vibration. was determined based on the theoretical injection depth and the inclination of the pipe relative to the These pipes are afterwards used for injection so they are equipped with close valves at the toe to vertical axis. Allowed tolerance for deviations is ±10 cm. prevent the obstruction of the pipe as it is being installed in the soil. The length of the injection pipes 5.2. The Resin Injection Process was determined based on the theoretical injection depth and the inclination of the pipe relative to the vertical axis. Allowed tolerance for deviations is 10 cm. Once the pipes are installed, the injection of the resin begins immediately. The resin is injected using and “injection gun” that is fitted to the upper end of the installed injection pipe. The two 5.2. The Resin Injection Process components of the resin are transported separately to the “injection gun" and mixed under high Once the pipes are installed, the injection of the resin begins immediately. The resin is injected using and “injection gun” that is fitted to the upper end of the installed injection pipe. The two components of the resin are transported separately to the “injection gun" and mixed under high Appl. Sci. 2018, 8, 1117 9 of 11 pressure in a chamber located at the rear. This ensures a perfect mixture of the two components before Appl. Sci. 2018, 8, x FOR PEER REVIEW 9 of 11 the mixture is added to the injection pipe and then into the soil. This process continues at each injection point until the lifting of the structure is first observed. pressure in a chamber located at the rear. This ensures a perfect mixture of the two components Lifting is the element that makes it possible to check the injection efficiency in real time. before the mixture is added to the injection pipe and then into the soil. This process continues at each injection point until the lifting of the structure is first observed. 5.3. Instrumentation and Control of the Injection Lifting is the element that makes it possible to check the injection efficiency in real time. A laser level with accuracy up to 0.1 mm was used to control the lifting of the structure, which also 5.3. Instrumentation and Control of the Injection made it possible to detect vertical movement during the injection. This is considered a real time A laser level with accuracy up to 0.1 mm was used to control the lifting of the structure, which monitoring (see Figure 3). also made it possible to detect vertical movement during the injection. This is considered a real time The laser level was positioned at a certain distance from the injection point to prevent it from monitoring (see Figure 3). being affected by the injection process. The set-up consists of the level and various targets attached The laser level was positioned at a certain distance from the injection point to prevent it from to the structure to be treated. These targets detect variations in the lift respect to the fixed horizontal being affected by the injection process. The set‐up consists of the level and various targets attached reference plane set by laser. to the structure to be treated. These targets detect variations in the lift respect to the fixed horizontal The interruption or cessation of the injection process is determined based on this monitoring, reference plane set by laser. which allows controlling lifting and to avoid unwanted movement. The best evidence of the The interruption or cessation of the injection process is determined based on this monitoring, effectiveness which allof owthe s cont injection rolling li isft the ingliftings and to avoid recorded unin wanted mov the control ement. The systems. best evidence of the effectiveness of the injection is the liftings recorded in the control systems. 6. Results Obtained 6. Results Obtained Following the injection, a geotechnical study was conducted using DPM (Dynamic Probing Following the injection, a geotechnical study was conducted using DPM (Dynamic Probing Medium) (AENOR-CEN, 1993) in order to verify the improvements achieved in terms of the Medium) (AENOR‐CEN, 1993) in order to verify the improvements achieved in terms of the load-bearing capacity of the soil. These dynamic penetration tests were carried out at the same site and load‐bearing capacity of the soil. These dynamic penetration tests were carried out at the same site with the same equipment that was used to characterize the soil prior to injection. This comparative and with the same equipment that was used to characterize the soil prior to injection. This study shows the improvement to the soil in terms of penetration resistance, which is indicative of the comparative study shows the improvement to the soil in terms of penetration resistance, which is load-bearing capacity of the treated soil (Figure 7). indicative of the load‐bearing capacity of the treated soil (Figure 7). Figure 7. Penetrometric tests performed before and after injection. Figure 7. Penetrometric tests performed before and after injection. Appl. Sci. 2018, 8, 1117 10 of 11 7. Conclusions 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]. The injection of polyurethane resins has a different behavior, due to the chemical nature of its components, polyurethanes. In fact, they do not require any injection pressure and during the synthesis reaction a certain amount of carbon dioxide is generated which causes the volumetric expansion of the mixture (Figure 1). The solidified resin reaches the natural balance with the surrounding soil, when the pressure of swelling of the resin, resulting from the reaction, coincides with the average pressure of the confinement of the ground. The capacity of propagation of the resin in the different types of soil, can be established according to the following criteria. In gravels and sands the propagation is, mainly, by impregnation of the intergranular spaces. In clays, the voids and fractures present in the macrostructure of the soil are saturated by the resin, or compressed by the swelling pressure during the expansion of the mixture. The injection of expanding polyurethane resin into the soil is a technology for soil improvement that is also used for correct differential settlement in building. It is noteworthy that, because is a non-destructive method, this technology is especially suitable for historic buildings which are part of the country’s architectural heritage. The principle of the technology is based on the injection of a certain volume of expanding polyurethane resin into the soil, below the foundation bearing surface which then expands, displacing the soil around the injection site [15,16]. The expansion is accompanied by a reduction in swelling pressure and an increase in the average confining stress. The process stops when it reaches the equilibrium pressure. The resin penetrates into the terrain to be treated, increasing in volume and compressing the soil in all directions (radial expansion) favoring the pathways that offer the least resistance [3,4]. The resin continues expanding until the soil prevents any further radial compression. At that point, the only possibility for expansion is an upward displacement. This process continues at each injection point until the lifting of the structure is first observed. When the initial lifting is observed, it means that the consolidating action is being directed vertically upward and that this is the direction that offers the least resistance, while the surrounding soil offers greater resistance in respect of the decrease in the structural load. This shows that the foundation soil has been compacted enough to withstand not only the increase of static loads, but also the loads developed as a result of the lifting [16]. Due to the recent implantation in Spain of this technology, it is not possible to prove the efficacy of long-term treatment (more than 10 years). But new dynamic penetration tests and supervisions of the stabilized building are demonstrating that the mechanical properties of the treated ground continue being stable and that they have not diminished in the three years passed since the treatment. Author Contributions: F.E.S. conceived and designed the experiments; J.R.S. performed the experiments; F.E. and A.M.d.l.S. analyzed the data. All authors collaborated on the interpretation of the results and on the preparation of the manuscript. Funding: This research was funded by URETEK. Acknowledgments: The authors would like to thank URETEK for funding the research project titled “Method Injecting Expanding Polyurethane Resin in Different Types of Soil” carried out at the School of Civil Engineering at the Polytechnic University of Madrid, as well as the technical documentation provided. Conflicts of Interest: The authors declare no conflict of interest. Appl. Sci. 2018, 8, 1117 11 of 11 References 1. Escolano Sánchez, F.; Bueno Aguado, M.; Fernández-Ordóñez, D. The Finite Elements Method (FEM) Versus Traditional Methods (TM), in the Estimation of Settlement and Ballast Coefficient Calculation for de Design Slabs in Problematic Areas. Informes de la Construcción 2015, 67, 69–80. [CrossRef] 2. Faezehossadat, K.; Budiman, J. Expansive Soil: Causes and Treatments. J. Civ. Eng. 2016, 3, 1–13. [CrossRef] 3. Buzzi, O.; Fityus, S.; Sasaki, Y.; Sloan, S. Structure and Properties of Expanding Polyurethane Foam in the Context of Foundation Remediation in Expansive Soil. Mech. Mater. 2008, 40, 1012–1021. [CrossRef] 4. Buzzi, O.; Fityus, S.; Sloan, S.W. Use of Expanding Polyurethane Resin to Remediate Expansive Soil Foundations. Can. Geotech. J. 2010, 47, 623–634. [CrossRef] 5. Escolano Sánchez, F.; Mazariegos, A. Evaluation of the Risk Associated with Karstic Processes in Miocene Gypsum in South-Eastern Madrid Spain. Acta Carsol. 2015, 44, 251–263. [CrossRef] 6. Nowamooz, H. Resin Injection in Clays with High Plasticity. C. R. Mécanique 2016, 344, 797–806. [CrossRef] 7. Jimenez Salas, J.A. Propiedades de los Suelos y de las Rocas; Rueda: Madrid, Spain, 1975; pp. 153–218. ISBN 84-7207-008-5. 8. Mazariegos, A.; Escolano Sánchez, F.; Sánchez, J.R. El Estudio Geotécnico, Campaña de Campo y Ensayos de Laboratorio, 1st ed.; Garceta: Madrid, Spain, 2015; pp. 154–196. ISBN 978-84-1622-824-9. 9. Manassero, M.; Dominijanni, A.; Foti, S.; Musso, G. Design, Construction and Controls of Soil Improvement Systems. In Proceedings of the XXIV Edition of the Geotechnical Conference (Ciclo delle Conferenze di Geotecnica di Torino—XXIV CGT), Torino, Italy, 25 February 2016; Pàtron Editore: Bologna, Italy, 1925. 10. Escolano Sánchez, F.; Bueno Aguado, M.; Lavín, J.R.S. Interpretation of the Pressuremeter Test Using Numerical Models Based on Deformation Tensor Equations. Bull. Eng. Geol. Environ. 2014, 73, 141–146. [CrossRef] 11. Henderson, T.O.; Taylor, R.N.; Harris, D.I.; Mair, R.J.; Love, J.P. Observations of Ground and Structure Movements for Compensation Grouting During Tunnel Construction at Waterloo Station. Géotechnique 1994, 44, 691–713. [CrossRef] 12. Vinson, T.S.; Mitchell, J.K. Polyurethane Foamed Plastics in Soil Grouting. J. Soil Mech. Found. Div. 1972, 98, 579–602. 13. Salgado, R.; Mitchell, J.K.; Jamiolkowski, M. Cavity Expansion and Penetration Resistance in Sand. J. Geotech. Geoenviron. Eng. 1997, 123, 344–354. [CrossRef] 14. Escolano, F.; Mazariegos, A.; Sánchez Lavin, J.R. Underpinning of Shallow Foundations by Expansive Polyurethane Resin Injections. Case Study: Cardinal Diego de Espinosa Palace in Segovia (Spain). Revista de la Construcción. J. Constr. 2017, 16, 420–430. [CrossRef] 15. Yu, H.S.; Houlsby, G.T. Discussion: Finite cavity expansion in dilatant soils: Loading analysis. Géotechnique 1992, 42, 649–654. [CrossRef] 16. Apuani, T.; Giani, G.P.; D’Attoli, M.; Fischanger, F.; Morelli, G.; Ranieri, G.; Santarato, G. Assessment of the Efficiency of Consolidation Treatment through Injections of Expanding Resins by Geotechnical Tests and 3D Electrical Resistivity Tomography. Sci. World J. 2015, 2015. [CrossRef] [PubMed] © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Applied Sciences – Multidisciplinary Digital Publishing Institute
Published: Jul 11, 2018
You can share this free article with as many people as you like with the url below! We hope you enjoy this feature!
Read and print from thousands of top scholarly journals.
Already have an account? Log in
Bookmark this article. You can see your Bookmarks on your DeepDyve Library.
To save an article, log in first, or sign up for a DeepDyve account if you don’t already have one.
Copy and paste the desired citation format or use the link below to download a file formatted for EndNote
Access the full text.
Sign up today, get DeepDyve free for 14 days.
All DeepDyve websites use cookies to improve your online experience. They were placed on your computer when you launched this website. You can change your cookie settings through your browser.