The features of the implementation of injection technologies using polymer-based compositions with adjustable parameters for underground construction. Part I

Review article

Ter-Martirosyan A.Z., Anzhelo G.O., Alexeev V.A. The features of the implementation of injection technologies using polymer-based compositions with adjustable parameters for underground construction. Part I. Nanotechnologies in construction. 2025;17(4):466–474. –474. – EDN: CWCJQO.

Тер-Мартиросян А.З., Анжело Г.О., Алексеев В.A. Особенности реализации инъекционных технологий составами на полимерной основе с регулируемыми параметрами в подземном строительстве. Часть I. Нанотехнологии в строительстве. 2025;17(4):466–474. –474. – EDN: CWCJQO.

In recent years, injection technologies have seen increased utilization in the context of underground construction in the Russian Federation and internationally [1, 2]. These technologies have been implemented as an independent process [3, 4] with the objective of ensuring the safety of buildings and structures [5, 6]. A substantial number of Russian and foreign projects have been executed in civil, hydraulic engineering, transport construction, and mining facilities, thereby substantiating the efficacy of various injection systems in addressing soil mass stabilization, the establishment of ground water cutoffs, the restoration of waterproofing systems, compensation grouting, and soil stabilization through injection [7, 8].

Consequently, in the construction of transport infrastructure facilities in Moscow, soil stabilization and compensation grouting technologies are extensively employed to maintain the initial stress-strain state of the soil mass [11, 12] and stabilize settlements in the area of influence [13, 14]. During the injection process, the properties of the soil in the area treated with injection compounds undergo substantial changes [15, 16].

The injection of distinct hardening mixtures into the ground, contingent on the method employed [17, 18], enables the control of the soil’s SSS [19, 20] and the en-

APPLICATION OF NANOMATERIALS AND NANOTECHNOLOGIES IN CONSTRUCTION hancement of its physical and mechanical properties. This approach facilitates the resolution of numerous challenges, including the stabilization of soil [6, 10], the augmentation of its waterproofing capacity [21], and the implementation of specialized construction methodologies [22, 23].

In instances where the bearing capacity of foundation bases proves inadequate, it is feasible to proceed with the injection process without compromising the ongoing construction work [20, 24] or as a component of a reconstruction [20, 25]. It is postulated that, under the condition that the soil thickness is maintained between 5 and 10 meters, the utilization of compact equipment and mixing and injection equipment is adequate. This approach offers distinct advantages when engaging in construction activities on lower and basement floors of buildings, as well as in basements and pits that are in close proximity to the foundation levels.

An analysis of the technologies employed and the projects implemented reveals patterns of use, primarily in the injection of mineral solutions based on various modifications of inorganic binding agents. When injecting low-strength dispersed soils or fractured rock masses with a loose structure and high specific water absorption during hydrostatic testing, mineral solutions often spread along the channel of least hydraulic resistance [26], which is associated with the peculiarities of their hydration (since in water-saturated environments, the true water-cement ratio changes due to dilution with water, which affects the hardening dynamics and final strength parameters) and the actual change in the concentration of the binding agent in the volume of the hardening mass [27, 28]..

It has been repeatedly noted that in complex engineering-geological conditions with high water saturation of the mass, the presence of layers of weak soils with low physical and mechanical characteristics, the process of injecting mineral systems gives rather unpredictable results [16, 27], which often requires preliminary treatment with polymer compositions or complete replacement of the injection mixture with polymer-based injection materials with adjustable parameters [25, 29].

However, a review of recent studies [25, 30], as reflected in the works of various authors [31, 32], indicates a paucity of research on the influence of the flow rate and method of injection of polymer mixtures on the properties of stabilized soils. There is a lack of standard methods for different compositions with predictions of the properties that can be achieved [31, 33], which is particularly salient during the design and budgeting stages of a construction project [31, 34]. The findings of Russian scientists’ laboratory studies on the chemical stabilization of soils with polymer compositions have not been widely disseminated. The properties of geopolymers can exhibit both low and excessively high strength characteristics. The high instability of the stabilized mass frequently precludes its consideration as a reliable foundation.

The primary polymeric materials utilized for injection applications are epoxy and polyurethane compounds. Previously, carbamide, phenol-formaldehyde, furan, and methacrylate resins were also utilized; however, they are now practically unused due to the high toxicity of the compounds, which particularly complicated work in confined spaces (tunnels, mines, basements, buildings) [35, 36].

Despite the utilization of carbamide or urea-formal-dehyde resins at several facilities, these materials necessitated substantial expenditures for the implementation of worker protection measures. These measures included the establishment of forced ventilation systems, the employment of protective goggles, gas masks, and respirators [35, 36]. Carbamide resins of various modifications are derivatives of urea and are products of the polycondensation of formaldehyde (CH2O) with urea (carbamide CO(NH2)2) or its derivatives, including thiourea and melamine. The outcome of this process, contingent upon the condensation conditions (temperature, pH of the medium), is the generation of either insoluble, non-melting compounds or soluble, meltable products. These products manifest as a cloudy, homogeneous syrup-like liquid that can be further utilized through injection into the soil [37, 38].

Furan resins are thermosetting oligomers that are formed from compounds containing a furan ring. They are capable of slow hardening under normal conditions (excluding resins consisting of furfuryl and acetone-based monomers, such as furfurylidenacetone). However, they harden rapidly when heated (150÷170 °C) or (and) in the presence of catalysts (mainly aromatic sulfonic acids or mineral acids). They form heat-, acid- and alkali-resistant materials characterized by a high coke number k (up to 85÷90%).

Methacrylates are defined as mixtures consisting of acrylic and methacrylic resins. A subset of acrylates find application in the capacity of waterproofing sealing materials, a function that encompasses the mitigation of deformation and cold joints, and the elimination of water seepage [39].

A promising direction in this regard is the reduction of resin toxicity for wider use in construction technologies. This objective requires the establishment of new, more stringent toxicity parameters for the compositions used and their modification by manufacturers to meet these requirements.

Injections of epoxy compounds as a stabilizing agent in fine- and medium-grained alluvial sands with a filtration coefficient Kf = 5–15 m/day result in the achievement of uniaxial compressive strength of stabilized samples within the range of 0.5–2.5 MPa and a density in the range of 1.85–2.15 g/cm3 [40, 41]. A notable disadvantage of epoxy resin injection is its inadequate water resistance during the structural strength gain phase. This property is particularly deleterious in instances of hardening processes occurring in

APPLICATION OF NANOMATERIALS AND NANOTECHNOLOGIES IN CONSTRUCTION water-saturated soils with high humidity, a common occurrence in the central region of the Russian Federation. The development of the chemical industry in foreign countries has enabled the reduction of the reliance on epoxy-based mixtures and environmental humidity. This reduction has been achieved through the use of various additives and modifications to the compositions. Consequently, there is considerable potential for domestic manufacturers to enhance the properties of epoxy mixtures through scientific and technological advancements [42, 43].

A comprehensive analysis of data from diverse sources has been conducted, and the results indicate that soils stabilized with polymer soil systems attain their intended design values. Modern polyurethane compositions [30] are the most prevalent, exhibiting a sufficiently extensive range of properties, thereby enabling their application in addressing various challenges. However, there is a paucity of uniform requirements for the technological parameters of methods for injecting hardening polymers into soils, requirements for them, or limits on their use.

MATERIALS AND METHODS

The study analyzed the use of polymer injection compositions in underground construction, which can be considered as basic solutions for many tasks:

• 1.    Soil stabilization technologies (improving their physical and mechanical properties, increasing waterproof capacity, creating additional stress in soils – during compensation grouting). The technology should distinguish between injections into different types of soils (dispersed, clayey, fractured rock masses), each of which has its own characteristics.

• 2.    Elimination of water seepage and active leakages in underground structures by injection into the contact area between the structures and the soil mass (see Fig. 1).

• 3.    Injection into cracks in concrete structures for the purpose of sealing them should also be mentioned separately (not considered in this study).

For the study, a substantial sample of open sources was analyzed, and the most prevalent technology for injecting polyurethane compositions was selected for analysis (as more widely reflected in a number of publications). This technology is widely used in both foreign and domestic practice and primarily involves the use of a polyurethane injection mixture – a product of the reaction of polyol and isocyanate, mixed in specific volume proportions, which is then injected into various media. The resulting one- or two-component mixture at the conclusion of the chemical reaction becomes a polymer that increases in volume by more than 20 times under specific conditions. Conversely, there are modifications that exhibit minimal expansion (have a foaming coefficient close to 1.0). As is the case with conventional materials, polyurethane mixtures undergo a decrease in their physical and mechanical properties as their porosity increases. However, during the expansion process, these materials have the potential to generate local pressure in the soil up to 10 MPa. This pressure results in the consolidation of the soil within the injection zones, thereby enhancing its strength in the area affected by the treated soil. The resulting polyurethane resin belongs to the category of closed-cell foam materials in the form of irregular polyhedrons with a density of 30–35 (for polyurethanes with 30 times expansion) and over 1200–1300 kg/m3 (for polyurethanes with virtually no expansion). The closed pore structure of hardened

Fig. 1. Water seepage in underground structures in the contact area, as well as through concrete body, leaks, fissures, and cracks

APPLICATION OF NANOMATERIALS AND NANOTECHNOLOGIES IN CONSTRUCTION polyurethane foam renders it relatively resistant to water absorption, making it a suitable material for various applications in construction, including bulk soil stabilization, water displacement, the creation of ground water cutoffs, and the mitigation of emergency situations (see Fig. 2, 3). This material has been demonstrated to effectively suppress active leaks and water seepage (see Fig. 1). This compendium of potential applications designates polyurethane compositions as the most versatile injection mixtures, enabling the execution of a broad spectrum of tasks through the modulation of their properties. However, there are a number of issues that are not addressed in the regulatory documentation for injection technologies using polymer materials, which requires scientific and technical support and experimental and empirical modeling during project implementation [44, 45].

To increase strength and control the stabilized zone, a two-component injection technology is commonly used, which involves injecting a highly elastic, fast-reacting two-component compound. Unfortunately, there is virtually no laboratory experimental research on the dependence of the deformation and strength properties of stabilized soil on the method of injection of polyurethane compositions with different characteristics and injection parameters, which is particularly important for further work. This is due to the lack of both methods and relevant experience, given the recent emergence and introduction of stable injection polymer systems with predictable properties.

It is hypothesized that the most effective method for consolidating sandy soils of various sizes through impregnation involves the injection of polyurethane compositions with the minimal foaming coefficients. This approach yields sufficiently strong masses that exhibit uniaxial compression strengths ranging from 5 to 10 MPa. The utilization of expanding polyurethanes in sands has also been demonstrated to be quite effective. This efficacy is attributed to the following mechanisms:

Fig. 2. Breakthrough of pressurized water from waterbearing layers through the bottom of the excavation pit the effect of compacting sand particles, the cutting off of large and medium water-saturated water channels with water displacement, and the filling of these channels with a hardening polymer. In the context of polyurethane compositions injected into clay soils, the primary objective is to achieve mass compaction, thereby enhancing its deformation properties. When the design pressure is increased and compositions with an expansion coefficient > 5–10 are used, a compensation injection effect may occur, which is used to solve a number of geotechnical problems. For dispersed and clayey soils, there is no clear methodology for design solutions for the injection of polymer compositions (despite the significant amount of experience gained from completed projects), criteria for design justification, or requirements for technology parameters and materials used.

The most predictable process is the injection of polymer polyurethane mixtures into fractured rock-type soils with tamping and complete blockage of fractures after injection, commonly used to increase the water resistance of the rock mass (the task of improving the physi-

Fig. 3. Breakthrough of running sand through the excavation pit fence

APPLICATION OF NANOMATERIALS AND NANOTECHNOLOGIES IN CONSTRUCTION cal and mechanical characteristics of rock foundations rarely arises and is more typical for destroyed, highly fractured or karstified rocks, the task of strengthening which is more effectively solved by injections of mineral compositions), mainly used in mining [26, 27, 35]. By selecting the structure formation parameters for optimal reaction rates and volume expansion of compositions for different types of porosity (with different diameters of conditional pore channels, branching and connectivity of rock mass fractures, hydrostatic pressure in the soil mass, and thickness of the layer to be stabilized), it is possible to solve the problem of increasing the water resistance of fractured rocks to practically complete water resistance, comparable to low-grade concrete.

The technology for performing injection work for buildings and structures in industrial and civil construction usually consists of the following stages: drilling wells and their arrangement; installing a packer injector in the packer column, installing a double packer in the injection zone, and the injection itself. Variations of this technology include injection through a drilling assembly (the drilled section is perforated, through which the mixtures are injected into the soil) and injection through driven picks, when the injection is carried out through the lower part of the metal pick as it is gradually extracted by lifting equipment. The most controllable technology is the packer technology, since the injection pipes are equipped with rubber cuffs that act as a check valve, preventing the solution from flowing back from the well into the injector when the pressure drops, and the annular solution prevents flow between injection horizons, allowing the specified injection points to be treated with a single injection of a certain volume or in several stages of a distributed volume, depending on the type of task to be solved.

In the course of implementing major projects for the construction of Moscow Metro facilities from 2013 to 2024, emergency measures were implemented and anticipated occurrences were eliminated during the construction of underground structures. These measures included the enclosure of excavation pits to prevent flooding (both through enclosing structures and through the bottom/ foundation being developed in stages) (see Fig. 2, Fig. 3), the mitigation of breaches in structural integrity – structures’ joints loss of tightness (entrance/exit of TBM into station pits), the elimination of leaks and water seepage in tunnels [39], and the stabilization of building and structure foundation soils [16, 32] in the affected area. The design solutions developed for a range of tasks in emergency situations allow the following prerequisites to be established:

– in the context of operational implementation of measures to stabilize soils and restore anti-filtration properties, polymer materials are preferable due to their faster strength gain compared to mineral compositions. In general, polymer compositions reach their final char- acteristics in 6 to 24 hours, while mineral compositions require 7 to 24 days to reach the same point;

– faster strength development of polymer mixtures allows working both in sections and across the entire working face, and in emergency situations concentrated in one area, allows working from a limited number of wells;

– in conditions of high water inflow and hydrostatic pressure, even when it is necessary to inject cement compositions, it is most optimal to pre-inject fastreacting polymer compositions to prevent washouts, plug potential outlets, and relieve hydrostatic pressure;

– when eliminating water seepage in mating structures, such as joints between tunnel lining blocks or the “tunnel-pit” or “tunnel-stall gate/breakthrough” joints, polymer materials are preferable due to their higher elasticity under certain permissible movements, since the use of cement compositions during movement forms cracks that act as water inflow channels, and to prevent such cracks from forming, it is necessary to create a sufficiently large fixed array with large injection volumes.

To analyze the formation of another aspect of the implementation of polymer composition injections – when restoring the waterproofing properties of structures – the requirements are partially formulated in the provisions of GOST 33762-2016 “Materials and systems for the protection and repair of concrete structures. Requirements for injection and sealing compounds and seals for cracks, cavities, and fissures” in terms of adhesive and sealing closure or compression and sealing closure (groups AS, CS), but there are no methods for eliminating active leaks, water penetration through structures other than cracks in concrete, etc.

In order to ascertain the mechanisms of injection polymer mixtures injected into dispersed and clayey soils for the purpose of their stabilization, it is also necessary to establish requirements for them, develop regulatory requirements, and determine the optimal quality control measures that provide an unambiguous assessment of the achievement of design objectives.

The research was carried out using the material and technical resources of the Main Regional Center for Collective Use of Scientific Equipment and Installations of the Moscow State University of Civil Engineering, with the support of the Ministry of Science and Higher Education of the Russian Federation (agreement No. 075-152025-549). In addition, as part of the research conducted under the NIU MGSU Development Program for 2025– 2036, within the framework of the Priority-2030 Strategic Academic Leadership Program, it is planned to develop methodological recommendations for soil stabilization and elimination of active leakages during the construction and operation of underground structures.

To be continued.

APPLICATION OF NANOMATERIALS AND NANOTECHNOLOGIES IN CONSTRUCTION