Chemical Grouting

Definition:

Chemical grouting is a process of injecting specialized chemical grouts into the ground or structures to enhance their properties, such as strength, impermeability, and stability. The chemical grouts react and solidify within the ground, forming a durable and stable mass.

Uses/benefits:

Chemical grouting offers several uses and benefits in tunneling and underground structures:

Ground Stabilization: Chemical grouting is used to stabilize and strengthen the surrounding ground, particularly in loose or unstable soil conditions. It improves the load-bearing capacity and shear strength of the ground, enhancing the stability of tunnels and underground structures.
Water Control: Chemical grouts can be injected to control water ingress into the tunnel or underground structure. The grouts form a watertight barrier, preventing the inflow of groundwater, reducing water pressure, and minimizing the risk of water-related issues such as seepage or erosion.
Void and Fracture Filling: Chemical grouting is effective in filling voids, fractures, and cavities in the ground or existing structures. It provides structural integrity by filling these spaces, reducing the risk of settlement, and improving the overall stability of the tunnel or underground structure.
Soil Consolidation: Chemical grouting can be used to consolidate loose or granular soils by permeating and solidifying the soil particles. This improves the engineering properties of the soil, such as cohesion, compaction, and resistance to erosion.
Ground Improvement: Chemical grouting is often employed to improve the ground conditions in advance of tunneling. It can modify the soil characteristics to achieve the desired engineering properties, ensuring safer and more efficient tunnel construction.

Specifications:

Specifications for chemical grouting may vary depending on the specific project requirements, ground conditions, and the type of chemical grout used. Some common specifications include:

Gel Time: The gel time specifies the time it takes for the chemical grout to solidify and reach its full strength. It is important to consider the gel time to ensure sufficient penetration and reaction of the grout within the ground.
Viscosity: The viscosity of the grout determines its flow properties and penetrability into the ground. The appropriate viscosity is selected based on the soil permeability and injection method.
Setting Time: The setting time of the grout refers to the time it takes for the grout to harden and achieve its final strength. The setting time should be compatible with the project schedule and construction requirements.
Compatibility: The chemical grout should be compatible with the ground conditions, ensuring effective interaction and solidification. Compatibility tests and evaluations may be conducted to ensure optimal performance.
Environmental Considerations: It is important to consider any environmental restrictions or regulations regarding the use of chemical grouts. Some grouts may have specific limitations or requirements in terms of toxicity, biodegradability, or long-term effects on the surrounding environment.

Types:

Chemical grouts used in tunneling and underground structures can include the following types:

Polyurethane Grout: Polyurethane-based grouts are commonly used in chemical grouting. They expand and foam upon injection, filling voids and fractures and providing excellent water sealing properties. Polyisocyanates and polyalcohols react to form polyurethanes. These compounds can also react with other substances that have hydroxyl groups, such as polyethers, polyesters, and glycols.
Acrylic Grout: Acrylic grouts are water-based and have good adhesion properties. They are suitable for sealing fine cracks and stabilizing loose or sandy soils.
Epoxy Grout: Epoxy-based grouts offer high strength and durability. They are commonly used for structural repair, crack injection, and bonding applications in tunnels and underground structures.
Cementitious Grout: Cement-based grouts are used for various applications, including soil stabilization, water control, and void filling. They provide strength and rigidity once cured.
Silicate Grout: Silicate-based grouts chemically react with the ground to form a solid gel-like mass. They are effective in consolidating loose soils and preventing water ingress. Sodium silicate (n-SiO2 Na2O) is commercially available as an aqueous solution. The silica/alkali ratio ‘n’, if between 3 to 4, is more suitable for grouting.

IS 14343 - 1996: Choice of Grouting Materials for Alluvial Grouting - Guidelines, complies with the properties of various grout admixtures and various characteristics of commonly used chemical grouts.

The specific type of chemical grout selected depends on the ground conditions, project requirements, and the desired outcomes.