Ground improvement is a fundamental aspect of construction, rehabilitation, and repair of structures built on unstable soils. Traditionally, engineers have relied on methods such as piling, cement grouting, and ground freezing. However, advances in chemical technologies have introduced more efficient solutions that allow for targeted, fast, and cost-effective intervention.
One of the most effective approaches is the use of expanding polyurethane injection systems. This article provides a detailed analysis of their advantages, with a focus on underlying mechanisms, material behavior, and practical applications.
One of the most effective approaches is the use of expanding polyurethane injection systems. This article provides a detailed analysis of their advantages, with a focus on underlying mechanisms, material behavior, and practical applications.
Conventional Ground Improvement Methods: Capabilities and Limitations
Before comparing innovative solutions with traditional methods, it is important to review commonly used approaches:
Despite their widespread use, these methods have several limitations:
- Cement grouting: Injection of cementitious materials to increase soil density and bearing capacity
- Piles: Driven or bored elements transferring loads to deeper, more stable strata
- Geotextiles and geogrids: Synthetic materials used for load distribution and surface stabilization
- Ground freezing: Use of refrigerants to temporarily increase soil strength
Despite their widespread use, these methods have several limitations:
- Require extensive site preparation and mobilization of heavy equipment
- Often unsuitable for localized issues or targeted repairs
- Difficult to implement without disrupting ongoing operations
- Performance is sensitive to groundwater conditions, soil composition, and environmental factors
Mechanism and Advantages of Expanding Polyurethanes
Polyurethane injection is a well-established method for localized strengthening and stabilization of weak, compressible, and water-bearing soils. When the components are mixed, a rapid chemical reaction occurs, forming an expanding polymer matrix.
Key Advantages
- Fast reaction time: Expansion begins within seconds (typically 5–10 seconds for systems such as PolyJet FT), enabling precise material placement
- Controlled application: Pressure and expansion can be regulated to target specific zones and reinforce load-bearing areas
- Low invasiveness: No need for large-scale excavation or structural dismantling; work is performed through small-diameter injection points
- Performance in challenging conditions: Effective in saturated soils and chemically aggressive environments (acidic or alkaline)
- Time and cost efficiency: Typically 4–10 times faster than cement grouting, with reduced project costs due to shorter execution time and minimal equipment requirements
- Immediate load-bearing capacity: Strength improvement is achieved almost instantly, without curing time or operational downtime
Physico-Chemical Properties
Key material parameters include:
- Density: 1.1–1.2 g/cm³ (PolyJet FT)
- Viscosity: 200–250 mPa·s
- Expansion ratio: up to 32×
- Application temperature range: +3 to +40 °C
Mechanism of Action
Injection polyurethane systems are reactive polymers that rapidly form a closed-cell structure upon mixing, with or without the presence of moisture. This structure is capable of sustaining significant mechanical loads.
The expanding material fills voids, redistributes stresses, and displaces water from soil pores and capillaries, contributing to improved stability of the soil mass.
The expanding material fills voids, redistributes stresses, and displaces water from soil pores and capillaries, contributing to improved stability of the soil mass.
Comparative Overview (Repair Applications)
Practical Case Studies
Injection polyurethane systems have been successfully applied in numerous projects worldwide.
Case 1: Industrial Floor Stabilization
At a logistics facility, flooding caused settlement of concrete floor slabs. Conventional repair would have required full slab removal, resulting in a week of downtime and significant cost.
Instead, polyurethane injection was used:
Instead, polyurethane injection was used:
- Material injected beneath 30 slabs
- Floor restored to design elevation within 4 hours
- Cost savings of approximately 70%
- Total project duration — one working day
Case 2: Tunnel Sealing
In an urban metro system, water ingress caused erosion near sheet pile structures. Polyurethane injection enabled rapid formation of impermeable barriers, stopping inflow and eliminating the risk of failure within 12 hours.
Environmental and Health Considerations
Environmental performance is a key factor when selecting a stabilization method. Injection polyurethanes offer the following advantages:
All works are supported by appropriate certification, licensing, and compliance documentation.
- Do not release harmful substances during or after reaction
- Chemically inert in wet and aggressive environments
- Do not disrupt soil structure or natural balance
- Comply with applicable environmental and health standards
All works are supported by appropriate certification, licensing, and compliance documentation.
Regulatory Framework and Standards
Injection works are carried out in accordance with relevant standards and regulations, including:
Proper project documentation ensures seamless integration of the method into construction workflows.
- GOST 2761-84
- SP 22.13330.2016 — Foundations of Buildings and Structures
- Government Decree No. 87 (Russian Federation) — Project Documentation Requirements
- STO NOSTROY 2.3.18-2011 — Soil Stabilization by Injection Methods in Construction
- Manufacturer technical documentation
Proper project documentation ensures seamless integration of the method into construction workflows.
Conclusions and Recommendations
Both research and practical experience demonstrate that expanding polyurethane injection is an effective solution for fast, cost-efficient, and durable ground improvement.
The technology:
Recommendation:
Engage certified contractors, review project documentation carefully, and require verification of results through appropriate testing and monitoring.
The technology:
- reduces repair time and costs,
- minimizes environmental impact,
- ensures long-term performance and reliability.
Recommendation:
Engage certified contractors, review project documentation carefully, and require verification of results through appropriate testing and monitoring.
References and Standards
- GOST 2761-84 — Soils. Testing Methods
- SP 22.13330.2016 — Foundations of Buildings and Structures
- Government Decree No. 87 — Project Documentation Requirements
- STO NOSTROY 2.3.18-2011 — Soil Stabilization by Injection Methods in Construction
- Geotechnics Journal, No. 3, 2025