Foam underpinning and foam soil stabilization: injection of expanding polyurethane resin for strengthening structures and soils

Encountering a Weak ground or unsuitable soil is a possible challenge when considering a site for a construction project or in underpinning structures. They problem can arise due to the nature of the soil or the exposure of the soil to unsuitable environmental conditions. Soil stabilization is a proven method to improve the bearing capacity of the soil by implementing various geo mechanical and chemical methods.

 If the construction is in place and later it is found that the soil or the ground becomes unsuitable, proper underpinning methods can be selected to provide an effective solution.  Ground improvement using a polymer resin called polyurethanes is a novel method that is gaining popularity because it is nondisruptive, easy to install and cost effective compared to other methods. It can be used in  underpinning of buildings and improving weak grounds.

What are polyurethanes(PU) that are used in ground stabilization and underpinning

Polyurethane resins are a type of polymers that have been employed in geomechanics as a sealant to reduce seepage and other kinds of non-expanding resins (e.g. epoxy or acrylic) have more commonly been employed in grouting. 

The use of polyurethane as a filling and lifting agent has made it to be classified as a geosynthetic in the same category as of the geotextiles. However, It’s unconventionality lies in its mode of application which varies from other geosynthetics which are applied as pre-manufactured materials.

The application of polyurethane has a distinct procedure and set of equipment and requires skilled personnel because the material exhibits variable physical states of expansion. Polyurethanes can be composed to harden in different times and that affects their suitability for the types of intended works.

 Rapid-setting polyurethane is used in foundation and structure underpinning to immediately control the effects of lifting. Slow-setting polymers are used in soil stabilization that does not require monitoring its immediate effect. The equipment that is used for the rapid and slow setting are also different.

What are polyurethanes?

The class of polymers known as polyurethanes is versatile and can display a wide range of physical properties in both expanded and non-expanded states. Polyurethane resin is only sensitive to UV light and a few synthetic chemicals that are typically not present in foundation soils. Hence once injected into the ground it is regarded as stable or inert. However, polyurethane components are toxic in liquid form and must be handled with proper precautions.

The expansion of the polyurethane resins is caused by an exothermic reaction between a polyol and an isocyanate, which is blended in precise volumetric ratios according to specific product specifications. 

The reaction produces a substantial amount of carbon dioxide which is the agent that causes the volume expansion. The expanded resin forms a foam-like structure with hard walls that encase bubbles or cells.

The time of the reaction that turns the combined mixture from liquid to solid is very short though can be different depending on the mixed ratio, temperature, and use of catalysts. 

It is therefore feasible to adjust the temperature of the constituents to change the reaction time. Accordingly, polyurethanes are classified as slow setting and fast setting, which also make them applicable for different types of uses that we will mention later.

It is found that the pressure the resin exerts during expansion and the density of the expanded reason is related to the extent of expansion of the gas in the foam cells before the resin becomes solid.

The expansion pressure of the resin can reach 10,000 kPa and the reaction of the chemicals occurs very quickly. The resin develops its final physical-chemical characteristics in a few seconds

The physical and mechanical properties of polyurethane resin 

When expanding without confinement (free expansion), a polyurethane resin product can expand to a volume up to forty times larger than that of the original components. The bulk density in the free expansion is about 37 kg/m3. 

The confinement level determines both the final density and the produced expansion pressure. Under extremely constrained circumstances, pressures of up to 10 MPa and associated densities of up to 1000 kg/m3 can be achieved.

The specific resin and the temperature of the components will determine how long the reaction takes.  An expanding resin that hardens in a matter of minutes classed as the fast setting is ideal for foundation rehabilitation or underpinning applications, as it allows for the evaluation of the resin’s impact on the foundation level shortly after injection. 

The elastic modulus which is a measure of the stiffness of the foam resin after expansion and setting is comparable to any type of soil where a foundation or slab is built. Resin can have a value between 10 and 80 MPa depending on the density obtained after polymerization.

This comparable stiffness makes resin a suitable material for soil stabilization and underpinning because the resin and soil make a uniformly stiff end product.

Elastic modulus of soil materials compared with resin

The geotechnical application of expanding foam or resin in soil strengthening and underpinning

One innovative feature of polyurethane’s method of stabilization and underpinning is the non-disruptive and sustainable nature of the products and their applications. This method is suitable to stabilize the ground and floor of buildings when disruption of the premise is unfavorable.

 Do you know why this method of reinforcement of soil is preferable to conventional methods? The answer is its implementation does not interrupt the operation of the premise. This means that the daily normal functions of the affected building or structure can continue running as usual while the ground improvement technicians stabilize the floor. That is going to save money and prevent negative effects on the business activities while undertaking the needed work. 

The method of non-disruptive ground improvement is also gaining widespread use in stabilizing motorways. There is a unique advantage of the method also in roads and other transport infrastructure. This is because only one lane is required to be closed at a time, and only for a short distance – so that traffic can continue almost as usual during the repair work. 

Polyurethanes (PU) provide versatile solutions for various applications

1. Floor Lift: Elevate and level floors using polyurethane solutions for improved stability and functionality.

2. Floor Leveling: Achieve even surfaces with polyurethane applications, ensuring smooth and balanced flooring.

3. Straightening Sloping Floors: Rectify sloped floors by utilizing polyurethane techniques for a level and aligned foundation.

4. Lifting of Buildings: Employ polyurethane solutions to lift and stabilize buildings, addressing structural concerns effectively.

5. Lift of Grounds: Elevate and support ground surfaces through polyurethane applications for enhanced durability and load-bearing capacity.

6. Lift off Load-Bearing Walls: Enhance structural integrity by using polyurethanes to lift and reinforce load-bearing walls.

7. Lift-off Villas: Elevate and stabilize villa structures with polyurethane methods, ensuring long-lasting stability.

8. Floor Stabilization: Utilize polyurethanes to stabilize floors, providing a durable and secure foundation for various applications.

Liquid polyurethanes (PU) employed for soil reinforcement or void filling can be easily injected through small holes (12-16mm diameter). Upon polymerization, the material expands, exerting forces up to 10 MPa and effectively binding and consolidating the soil. This process enhances bearing capacity and stabilizes the soil.

High-density polyurethanes (PU) can exert forces up to 15 MPa, with a modulus of elasticity reaching 10-80 MPa. According to Uretek, a well-established foam resin underpinning contractor, the polymer is injected into the load-bearing area identified by the Boussinesq pressure bulb.

Pressure bulb under a foundation

Soil stabilization is successful in various soil types, including clayey, loamy, or sandy soils, demonstrating positive results in soil tests. The eco-friendly and hydrophobic nature of the material makes polyurethanes (PU) an excellent choice for waterproofing different construction projects.

Polyurethane applications vary based on ground conditions, necessitating tailored solutions considering soil type, specific issues, and working conditions. Common applications include ground strengthening, void filling, floor lifting, and waterproofing.

The suitability of Polyurethane resin solutions for Geotechnical problems due to differential settlement and expansive soils under structures

Expansive soils like sensitive clay pose a challenge to light-loaded structures. During moisture increase, these soils swell and cause deformations in substantial tilts, deflections, and bending. As a result, the soil can pose an unacceptable level of distress.

Underpinning improves a foundation’s stiffness and stability by adding structural elements, but full underpinning for existing structures is often impractical. Localized underpinning in specific problem areas may not address overall foundation issues, emphasizing the importance of a comprehensive understanding of the problem’s causes. 

Underpinning solutions can be disruptive and costly, posing challenges for effective and economical fixes compared to the replacement cost of the structure.

A specific category of foundation issues is common for a shallow foundation with light-loaded structures under the following conditions

– When it is built on an expanding soil that had irregular initial moisture conditions (for example, a tree that was cut down before building works are started

-The alternative scenario is if something alters the initial moisture equilibrium, like planting a tree.

– When constructing a slab, which has an impact on both moisture equilibrium and moisture exchange. 

-Another cause of problems is the natural spatial variability of soil expansiveness and/or depth.

 In such situations, differential foundation movements may occur as the foundation soils come to moisture and stress equilibrium beneath the new structure changes. The behavior of some types of soils particularly problematic clay soils changes with the status of moisture making stabilization and underpinning efforts unsuitable.

Expanding polyurethane resin injection offers a common alternative to underpinning, lifting structures without excavation or additional foundation elements by utilizing evolved gas pressure through chemical reactions.

Resin injection is a dependable restoration method with predictable results when differential settlements are caused by consolidation or settlement/collapse of fill.

But when injected into expansive soils, which frequently settle due to shrinkage brought on by water loss, concerns about the solution’s long-term effectiveness surface. It is possible to hypothesize that if the expanded soil is rewetted after being injected and releveled, it may swell excessively, over-lifting the already leveled house in that area. 

Geotechnical Applications of expanding resin or foam 

Polyurethane (PU) found geotechnical application in the following types of soil and structure strengthening projects. Generally, the resins are employed in soil stabilization, building and structure underpinning, and water proofing works.

Ground strengthening or stabilization by injection of polyurethanes(PU)

The settlement of grounds stems from factors like loads surpassing the soil’s bearing capacity or soil weakening due to environmental changes. Soil reinforcement emerges as a viable solution to mitigate the risk of buildings and structures sinking and settling.

Modern and innovative, soil reinforcement using polyurethanes (PU) enhances and stabilizes the soil’s bearing capacity directly beneath the foundation. The method eliminates the need for excavation, vibration, and other construction activities that disrupt the surroundings, consequently reducing costs and project durations.

Polyurethane injection into the soil, a contemporary approach to soil stabilization, involves introducing a polymer, typically polyurethane, to predetermined depths. This process enhances the soil’s mechanical properties, with the polymer entering the ground through impregnation, with or without fracturing.

Upon injection, the polyurethane material expands with a force of up to 10,000 kilopascals. As it expands, the geopolymer compacts and binds the surrounding soil, fortifying the ground and preventing sinking and settling issues for buildings and structures.

The injection of polymer provides an added advantage by proactively enhancing bearing capacity before a renovation project, ensuring foundation stability amid changes in building use.

This ground improvement technology, employing polymer injection, is versatile, applicable to almost all soil types, and effective in stabilizing various structures, including villas, apartments, historic structures, old buildings, churches, industrial facilities, production units, roads, railways, airports, and warehouses.

A notable feature of this technology is its capability to lift buildings and structures back to the desired level with millimeter precision if necessary.

Advantages of geotechnical soil reinforcement

As the works involve only drilling and injection no damage to the structure occurs

It is possible to plan works in specially selected spaces to avoid disturbance

The ground can be strengthened, sealed, and stabilized quickly and without disturbance.

It is possible to stabilize the soil and soil in just a few hours.

It is possible to inject polymer in a small, delimited area.

polyurethanes(PU) used are safe, as they do not dissolve in water or strain the surrounding soil and soil.

polymer is water-repellent and also binds the soil

Your business can be up and running at the same time as ground reinforcement is carried out

The solutions for soil reinforcement are fast, precise, and affordable alternatives.

Underpinning using expanding foam piles or columns 

Geotechnical piling is a technique employed to enhance the stability and support of structures by bolstering the bearing capacity of the underlying ground. A piled foundation serves to maintain the stability of the structure above it. This involves the insertion of piles from the surface into the ground, reaching down to a robust rock surface.

Typically, piling work becomes necessary when the uppermost layer of the ground lacks the strength required to sustain the construction of a new building or to support an existing one. In such instances, the piles are extended deep into the ground until they reach either rock or densely compacted soil.

Foam piles underpinning under a foundation

Underpinning using expanding foam versus the Traditional method of piling 

There are several different types of piles, depending on their use, material, price, and implementation. The common types of piles are classified as bearing, friction, or cohesion piles. The way the piles support the loads is different.

 Bearing piles transfer the loads to a hard-bearing layer or rock. Friction piles take advantage of the friction in cohesionless soil and in the case of cohesion piles, the cohesion in cohesive soils plays the role of counteracting the loads.

The traditional strengthening of the ground by piling uses the aforementioned types of piles. Hence, the works involve disruptive activities involving machinery like excavation, and hammering. This makes the environment dusty, noisy, and unavailable for conducting daily business or industrial activity.

Further, it is a time-consuming and costly solution because it involves demolishing, excavating, and installing piles.   The use of a polymer expanded pile spearheaded by companies such as Geobear is an innovative modern method that incorporates a casing of about 50mm diameter that is inserted through drill holes. 

The method uses a geotextile capsule through which polyurethanes(PU) are injected to strengthen the substructure with the use of expanding polyurethanes(PU). The injected polymer expands immediately and assumes the role of piles and it improves the compaction of the surrounding soil. This enables piling work to go faster and easier and produces no waste.

The expanding polyurethanes(PU) can be applied in grouting to a depth of 9 meters, under many different types of foundations. The polymer resin that makes up the polymer-expanded pillars can be injected directly under concrete slabs and building foundations. 

polymer pillars are ideal for areas that are difficult to access, as they do not require large piling rigs or load transfer structures. This piling method for ground reinforcement creates minimal disturbance through noise, dust, or general clutter. 

Furthermore, The polymer achieves 90% of its cure in just 15 minutes and 100% within 24 hours. This means that the reinforced area can be used immediately after finishing the installation. Polymer-expanded Piles can be used at different depths, both indoors and outdoors

Foam resin piling under a foundation

Advantages of expanded polymer Piling

– least cost and minimally disruptive piling projects. –

– results in less clutter and site disruption during the installation works

-Power piles can be used where traditional piling is not possible – they can even be installed indoors.

-clean, fast: because requires no excavation

-Precise: The work is planned, performed, and monitored with a high level of precision

-Environmentally neutral: because polyurethanes(PU) do not react with the environment

-Flexible concerning different depths and can also be used indoors

– The material can travel through hoses to the endpoint, so flexible point of application

-the application does not require mechanical force since the forces occur because of a chemical reaction

Filling of voids using polyurethanes(PU) to stabilize ground or soil

This technique of stabilizing soils, earth, or ground involves injecting polymer resin into areas experiencing stability issues. The chosen resin is a specially formulated, slow-expanding variant to minimize resistance. The primary goal is to fill voids in the ground, addressing or preventing settlement problems. The process includes monitoring ground elevation at various stations to ensure successful stabilization.

This method proves effective in treating settlement issues on asphalt and road surfaces caused by underground movements. The presence of potholes and cracks indicates ground instability, making it a suitable candidate for this approach. Polyurethanes (PU) are adept at filling voids of diverse shapes and sizes beneath the floor.

Tailoring the materials used for void filling depends on the size and location of the void. For addressing ground movement in railways, polymer injection easily resolves issues, enhancing line speed. Grouting employs lightweight materials that do not unnecessarily burden the underlying soil. The method’s advantages include preventing slab rocking, surface failure, and lateral rail movement.

Polyurethanes (PU) exhibit versatility in filling voids of any size or shape, making the method applicable to various scenarios such as basements, tunnels, sinks, caves, mines, shafts, pipelines, containers, cisterns, and channels.

Advantages of polymer void filling

– a very quick alternative to the traditional filling of empty voids.

– if later access is needed to the void, the polymer can be removed.

-it is possible to combine load-bearing solutions when filling voids. This can be led indirectly via a small hole, which offers a disturbance-free solution for the customer’s needs.

-A fast, efficient, and affordable solution with small carbon footprints

-unique, expanded polymer is very light and has good load-bearing properties.

-The original form of the polymer is in the liquid phase, and it can therefore be injected, pumped, or poured into voids, holes, or intermediate spaces 

-Produced on-site by a liquid base and can be poured, pumped, or injected into voids, holes, or intermediate spaces and can be easily transported over longer distances when needed.

-The polymer expands rapidly in its location with a brief gel time, displacing any remaining liquids. Additionally, it can be utilized underwater.

-The polymer can be removed so that the void can be opened up if necessary.

The repair work phases of the application

  1. Preliminary investigation

The volume and shape of the vacuum are determined. The appropriate repair methods are determined through a planning process.

  1. Preparations for installation

The underground installations of pipes and cables are identified and the utility supply lines are delineated. Then, the Layout and planning of the installation holes for grouting the polymer are determined.

  1. drilling of holes

holes of size 6-12mm are drilled with depths depending on the affected structure and ground conditions.

  1. The tubes are placed in the holes and the injection is done as necessary. Injection of a polymer intended for filling voids safely. The chemical reaction takes place at different speeds depending on the ground type and the material used.

Underpinning concrete slab Floor lifting using polymer resin injecting

Polyurethanes(PU) provides the best geotechnical solutions for floor lifting, floor leveling, and floor stabilization. The polymer is injected into the bearing layer under the floor slab. During hardening the polymer expands and this consolidates the bearing layer and thereafter raises the slab.

 Settlements occur under the building which can cause sinking, tilting, or create uneven floors. It is considered that it is expensive and difficult to straighten and lift floors that have sunk, but polyurethanes(PU) offer geotechnical solutions that are both faster and more cost effective than traditional methods.

Slab underpinning using foam resin

With proper planning the lifting can be done in just one day for small projects or with detailed planning that suits complex projects or when it is needed to have a convenient operation that does not interfere with the building use.

polyurethanes(PU) can also be applied to lift roads, streets, railways, and parking lots, and airport runways that have sunk or settled. If necessary, the work can be done at night and on weekends. This makes the solutions very suitable for businesses or places that cannot be closed again during the repair.

How is the floor lift done?

Floor leveling is done in a controlled and safe manner

The underground pipes, cables, and utility supply lines are first identified. Before lifting buildings or foundations, the problem is carefully examined geotechnically. Using various tests and geotechnical analysis it is ascertained whether the structure is still sinking, or whether the settlements have stopped.

 If the technicians determine that the settlement is still in progress, lifting is carried out together with the application of possible ground reinforcement. The soil reinforcement is carried out in-depth through the injection of polymer deep into the soil to increase the bearing capacity.

 The remaining issue of subsided structure or floor is lifted by the injection of the polyurethanes(PU) at a smaller depth from the surface. whereby the polyurethanes(PU) expand and compact the ground and then enable the lifting of the floor or structure above.

First, the work starts by drilling small holes through the floors or concrete slabs that have sunk. Then pipes are inserted and installed in the holes through which expanding polyurethanes(PU) are injected using pumps. The expanding polymer first fills all voids, compacts the soil, and results in the expansion and lifting of the floor structure that has sunk to the desired level.

During the execution of the works, the entire detailed process is monitored continuously by the use of laser meters. This ensures the lifting is executed safely and in a controlled manner.

The floor lifting and floor leveling can be executed very precisely, even with less than one-millimeter accuracy.

Advantages of geotechnical floor lifting

The method results in effective compaction of the bearing layer.

When lifting a floor or a building with polymer, no mechanical force is used. During the repair work, the floor does not need to be demolished. No excavation or large machines are required either.

The work does not involve disruptions of commercial or industrial activities.

The laser monitoring enables lift with millimeter precision. If necessary, floors and buildings can be lifted to 30 centimeters with the help of polyurethanes(PU). In addition, it is a cost-effective method compared to traditional methods of lifting a floor. It is dust-free and is a fast method.

 Steps of lifting of floor

  1. Settlement inspection for stabilization

Examination of the ground conditions and the reason why the floor or building has sunk. A settlement inspection is carried out so that all conditions are mapped and the geotechnical engineers can develop a specially designed solution for your particular lift.

  1. Design and planning

The engineering team develops the solution for lifting floors or buildings, which is best suited for the particular soil conditions and the specific project. Together, they plan project execution to minimize disruption while ensuring the desired result.

  1. Drilling and installation of grouting pipes

drill small holes, about 12 millimeters in diameter at regular intervals, through the floor tile that needs to be lifted. In the case of a lift of an outer wall or corner, of a building, drilling can often take place from the outside without drilling into the floor.

4. The grouting pipes are then installed in these holes. The floor does not need to be broken up, as the grouting holes are drilled in the joints between the tiles, if any. When the grouting is completed, the holes can be easily filled and sealed, so that the repairs do not leave any disturbing traces.

  1. Grouting and stabilization

polymer is injected into the soil in liquid form so that it can penetrate in a controlled manner into all voids under the entire slab, wall or structure to be lifted. When the polymer has filled the voids, it turns to the gel phase and finally solidifies completely.

During the repair process, the polymer binds any loose soil in the area and then expands to compact the soil and lift the floor. The lift is visible immediately and the geopolymer achieves full bearing capacity in about 15 minutes, then you can use the floor as usual again.

  1. Verification

The floor, building, or structure is monitored continuously and precisely throughout the grouting using a laser system of measurement.  With accurate laser measurement, it can immediately detect the slightest movement. When the floor or building is lifted, this is followed with very high precision. Careful monitoring is performed to the measurement but also of signs emitted by the building or floor, such as sound or visual signals to ensure that the lift is controlled and safe.

Waterproofing using polyurethanes(PU)

polyurethanes(PU) are also suitable candidates for preventing leakage. The waterproofing is done via screen injection which is becoming more common in several countries for sealing so that the risk of soil being washed away and water creeping into the structure’s susceptible areas is avoided. The increasing number of floods in recent years has created a need for preventive measures for water intrusion.

The process of waterproofing is made possible by the injection of polyurethanes(PU). The material is itself water-repellent and creates an impermeable barrier in the treated area. Once the polymer injection is completed, water or other liquids can no longer penetrate the secured area.

Therefore, the waterproofing method is applicable on construction sites, where a barrier against intrusion of water is needed to facilitate construction work in excavation works, for example in the case of a leaking sheet pile. Those Structures that are already below the water or groundwater level can also be screen-injected if there is a risk of water migration or erosion.

Polyurethanes (PU) are well-suited for preventing leaks, especially through a method known as screen injection. This technique is increasingly adopted in various countries to seal structures, minimizing the risk of soil erosion and water infiltration into vulnerable areas. The rising frequency of floods in recent years underscores the need for proactive measures against water intrusion.

The waterproofing process relies on the injection of polyurethanes (PU). This material inherently repels water, establishing an impermeable barrier within the treated area. Once the polymer injection is finalized, the secured area becomes impervious to water and other liquids.

This waterproofing method finds application on construction sites where a protective barrier is essential to facilitate excavation work, such as addressing leaks in sheet piles. Additionally, structures situated below the water or groundwater level can undergo screen injection when there is a potential risk of water migration or erosion.

Advantages of geotechnical waterproofing using polyurethanes(PU):

-Reduction of soil erosion.

-Immediate results for sealing against leakage.

-Avoid or prevent water intrusion.

-Environmentally neutral material.

-Fast and cost-effective method.

-No large and heavy machinery is required.

-No noise or vibration.

Equipment set for polyurethane resin injection

The complete equipment set for polyurethane resin injection can vary depending on the specific application, project requirements, and the characteristics of the polyurethane resin being used. Generally, the types of pumps and other accessories equipment commonly used in polyurethane resin injection are:

1. Injection Pumps:

-Single-Component Pumps: 

These types of pumps are used for injecting slow-setting Polyurethane resin for cases of grouting and waterproofing. PUR (1-C) from DSI underground offers a One-component polyurethane resins pump that is often used for smaller sealing work.

-Two-Component Pumps:

This type of pump is utilized for fast-setting polyurethane resins. These pumps are preferable for simultaneous and accurate dispensing of polyol and isocyanate.DSI Ground’s Two-Component Polyurethane Resins (PUR 2-C) pump, available at, stands out as one of the highly versatile injection resin systems. Primarily employed for sealing and stabilizing various structures, this system offers a wide range of applications and adaptability.

2.  Mixing System:

-Mixing head or nozzle for combining the polyol and isocyanate components just before injection.

-Static mixers to ensure thorough and homogeneous mixing of the two components.

3. Hoses and Fittings:

-High-pressure hoses to connect the injection pump to the mixing head.

-Various fittings and connectors for assembling the injection system.

4. Injection Ports:

-Ports or packers to create access points for injecting the polyurethane resin into the substrate.

5. Pressure Gauges and Monitoring Devices:

-Pressure gauges to monitor injection pressure.

-Flow meters to measure the volume of injected resin.

-Monitoring devices for real-time data on injection parameters.

6. Sealants and Plugs:

Sealants and plugs to close off injection ports after completing the injection process.

7. Safety Equipment:

-Personal protective equipment (PPE) including gloves, safety goggles, and appropriate clothing.

-Ventilation equipment if working in confined spaces.

8. Clean-up Tools:

-Solvents or cleaning agents for equipment maintenance and cleanup.

9. Quality Control Equipment:

-Testing equipment to assess the properties of the cured polyurethane resin.

-Inspection tools such as surveying equipment to evaluate the effectiveness of the injection process.

10. Documentation Tools:

-Recording devices for documenting injection parameters, volumes, and pressures.

-Cameras or inspection tools for visual documentation before, during, and after the injection process.

It’s important to note that the equipment used may be specialized based on the specific requirements of the project, and professionals should follow manufacturer guidelines and safety procedures when using polyurethane resin injection equipment. Additionally, the equipment set may vary for different types of polyurethane injection applications, such as soil stabilization, concrete repair, or waterproofing.

Planning and design of polyurethane resin injection

Planning and designing is the first important step for executing a foam underpinning project. One good example is the polyurethane resin injection for underpinning shallow foundations, as demonstrated in the case study of the Cardinal Diego de Espinosa Palace in Segovia, Spain.

 In this project, the following steps are taken to realize the implementation of the Foam resin restoration project:

  • Site Assessment:
    • Conduct a thorough inspection of the existing foundation and assess its condition.
    • Identify areas of settlement and determine the extent of underpinning required.
  • Soil Analysis:
    • Analyze the soil characteristics to understand its composition, bearing capacity, and potential for expansion.
    • Evaluate soil moisture content and other geotechnical factors affecting foundation stability.
  • Polyurethane Resin Selection:
    • Choose an appropriate polyurethane resin formulation based on the specific project requirements and soil conditions.
    • Consider factors such as viscosity, reaction time, and expansion properties.
  • Injection Point Placement:
    • Strategically determine injection points around the foundation, focusing on areas requiring underpinning.
    • Optimize injection locations to ensure uniform resin distribution and effective support.
  • Injection Process:
    • Use specialized injection equipment to introduce the polyurethane resin into the targeted zones beneath the foundation.
    • Monitor injection pressure and volume to control the resin flow and expansion.
  • Expansion and Stabilization:
    • Allow the polyurethane resin to expand and fill voids, compacting surrounding soils and providing additional support.
    • Ensure proper curing time to achieve optimal strength and stability.
  • Post-Injection Monitoring:
    • Implement post-injection monitoring techniques to assess the effectiveness of the underpinning process.
    • Conduct periodic inspections to verify that the foundation remains stable over time.
  • Documentation and Reporting:
    • Document each step of the injection process, including injection volumes, pressures, and any observed changes.
    • Prepare a comprehensive report detailing the planning, execution, and results of the polyurethane resin underpinning.

This systematic approach employed to polyurethane resin injection was likely instrumental in stabilizing and strengthening the shallow foundations, contributing to the preservation and restoration of this historic structure.

Expanding resin Injection Procedure:

  • Drilling Holes:
    • Holes, typically ranging from 12 to 26 mm, are drilled at intervals of 50 to 150 cm.
    • Metal pipes are inserted into these holes for injecting the liquid resin through them and that reach established depths.
  • Injection arrangement:
    • The injection arrangement involves two important parts. The first is where the resin injection head is located and the other is a laser level for lifting control.
  • Resin Injection:
    • The resin is injected in liquid form through pipes, undergoing a rapid chemical reaction that transforms it from liquid to solid with an expansion pressure of up to 10,000 kPa, completing the reaction in seconds. This radial expansion compresses the soil in all directions until further compression is restricted, followed by vertical displacement as the resin consolidates, lifting the soil upward.
  • Real-Time Effectiveness Confirmation:
    • Real-time confirmation of method effectiveness is achieved through continuous monitoring of the structure’s vertical movement.
    • The injection starts at the top level and proceeds to the next level as the resin mixture hardens.
    • Laser levels are employed post-injection to detect any vertical movement, ensuring the efficacy of soil treatment.
  • Measurement and Monitoring:
    • During injection, the amount of resin used is measured at each injection point.
    • Post-injection, laser levels monitor any vertical movement in the treated structure, providing a real-time efficiency check.

Pros and cons of foam underpinning

Pros of foam resin underpinning

-It does not modify the rigidity or distribution of force under the treated area. Therefore, the absence of “hard points” in the soil makes the resin injection process suitable for partial or localized treatment.

-Where differential settlements result from consolidation or settlement/collapse of fill, resin 

injection is a reliable remediation option with predictable outcomes.

-Faster than traditional methods


-Although the constituents can be toxic material the end product of foamed resin is environmentally neutral and does not affect groundwater quality.

-Disturbance-free, no excavation required

-Clean process that leaves no debris and residual material

Cons of foam resin underpinning

-Injecting in expansive soils such as reactive clay for leveling can have potential long-term undesirable performance, as re-wetting may lead to excessive swelling, risking over-lifting of already leveled structures.. 

-requires skilled professionals for implementation

-The constituents in liquid form are hazardous and need special care of handling.


The use of expanding polyurethane resin to remediate expansive soil foundations, Olivier Buzzi

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