Expanding Polyurethanes for Weak Soil Stabilization: A Scientific and Practical Perspective

Foundation stability is a critical factor in the safety and service life of buildings and infrastructure. Weak, water-saturated, disturbed, and collapsible soils present significant challenges in the design of industrial facilities, transport infrastructure, utilities, and residential developments.

Until recently, ground improvement relied primarily on conventional methods such as cement grouting, piling, and ground freezing. However, these approaches are often costly, time-consuming, and highly disruptive. This has driven the adoption of more efficient, controllable, and targeted solutions.

One such solution is the injection of expanding polyurethane resins, which enables rapid soil stabilization without excavation while delivering long-term performance.

Selecting an appropriate ground improvement method requires an understanding of soil behavior. Soil is a complex multi-phase system whose stability depends on composition, moisture content, density, and prior loading or disturbance.

Common Issues

• Foundation settlement
• Formation of voids due to particle washout
• Erosion caused by surface or groundwater flow
• Loss of bearing capacity under dynamic loading (traffic, industrial activity)

Conventional methods (grouting, piling, ground freezing, geosynthetics) have several limitations:

• Extensive site preparation requirements
• Long execution times
• Disruption of soil structure and environmental balance
• High implementation costs

By contrast, expanding polyurethane injection enables targeted strengthening with minimal time and resource input.

The application of expanding polyurethanes is a controlled engineering process. Its success depends on accurate site investigation, correct material selection, and precise execution.

A geotechnical assessment is carried out prior to injection using methods such as:

• Ground-penetrating radar (GPR)
• Static and dynamic testing
• Laboratory analysis of soil properties

These investigations identify the causes of settlement and void formation and define the scope of treatment.

The selection of resin and injection parameters depends on soil conditions, depth, and required performance. A commonly used solution is PolyJet FT, a two-component polyurethane system with rapid reaction and high expansion capacity.

The design process includes:

• Determining injection depth
• Defining injection points
• Calculating material volumes
• Establishing injection sequence

Injection is performed using precision equipment, with continuous control of pressure and flow rate.

• Density: 1.1–1.2 g/cm³
• Viscosity: 200–250 mPa·s
• Reaction time: ~5 seconds
• Expansion ratio: up to 32×
• Application temperature: +3 to +40 °C

The material adheres well to mineral substrates, is resistant to chemical and biological degradation, and performs reliably in challenging hydrogeological conditions.

Quality control includes:

• Incoming material verification
• Monitoring of injection parameters
• Post-treatment testing

The effectiveness of expanding polyurethanes is supported by both research and field applications:

• Fast execution: Typically 5–10 times faster than traditional methods
• Minimal disruption: No excavation or structural dismantling required
• High precision: Targeted treatment reduces unintended impacts
• Environmental safety: The material becomes inert after curing
• Durability: Service life exceeds 40 years, even under dynamic loading
• Cost efficiency: Reduced repair and maintenance costs
• Localized application: Suitable for partial repairs without interrupting operations

Objective: Eliminate settlement and voids beneath slabs in a 340 m² facility
Solution: Injection of PolyJet FT beneath each slab, achieving controlled lifting of 45–150 mm
Outcome:

• Floor restored to design level within hours
• Operations resumed immediately
• No measurable changes after 5 years
• Cost savings exceeding 70% compared to conventional repair

Objective: Restore bearing capacity beneath a structural column
Solution: Localized injection forming a dense composite of polymer and compacted soil
Outcome:

• Bearing capacity increased by 120%
• Confirmed by field testing
• No interruption to building operation

The environmental safety of polyurethane injection is confirmed by certification and compliance with applicable standards. The material does not release harmful substances, remains chemically inert in wet and aggressive environments, and does not degrade biologically.

Works are carried out in accordance with:

• GOST 2761-84
• SP 22.13330.2016
• Government Decree No. 87 (RF)

Proper documentation is essential, particularly for technically complex projects.

The use of polyurethane injection continues to expand:

• Rehabilitation of urban roads and paved areas
• Stabilization of tunnels and underground infrastructure
• Restoration of heritage structures
• Upgrading of utilities, industrial floors, and waterproofing systems

Advancements include integration into building standards and the development of automated monitoring systems.

Expanding polyurethane injection is an effective solution for stabilizing problematic soils. Both research and practical experience confirm its reliability and long-term performance.

Successful application depends on:

• thorough site investigation,
• proper engineering design,
• controlled execution.

Recommendation:
Engage experienced contractors, verify certifications, and ensure proper testing and monitoring of results.