Cement Grouting

Definition:

Cement grouting is the process of injecting a cement-based grout or slurry into the ground to improve the stability, strength, and permeability characteristics of the surrounding soil or rock formations in tunneling and underground structures.

Uses/benefits:

Cement grouting is commonly used in tunneling and underground structures for the following purposes:

Ground Stabilization: Cement grouting helps to stabilize loose or weak ground by filling voids, fissures, and fractures with a cementitious material. This improves the load-bearing capacity of the ground and reduces the risk of settlement or ground movement.
Water Control: Cement grouting can be used to control groundwater flow and prevent water ingress into the tunnel or underground structure. It creates an impermeable barrier that reduces water seepage and protects the structure from water-related damage.
Tunnel and Shaft Lining: Cement grouting is used to fill the annular space between the tunnel lining and the surrounding ground, providing additional support and increasing the integrity of the structure.
Soil Improvement: By injecting cement grout into the ground, the soil properties can be improved, including its shear strength, cohesion, and compaction. This is particularly useful in unstable ground conditions or where ground improvement is required.
Void Filling: Cement grouting is used to fill underground voids, such as abandoned mines or cavities, to prevent subsidence and ensure the stability of the surrounding area.

Specifications:

Specifications for cement grouting in tunneling and underground structures may vary depending on the specific project requirements, ground conditions, and desired outcomes. Some common specifications include:

Cementitious Material: The selection of the cementitious material depends on factors such as the required strength, setting time, and compatibility with the ground conditions. Portland cement is commonly used, but other types of cement, such as microfine cement or expansive cement, may be suitable for specific applications.
Water-to-Cement Ratio: The water-to-cement ratio determines the consistency and workability of the grout. It should be carefully controlled to achieve the desired flow properties and strength development.
Injection Pressure and Flow Rate: The injection pressure and flow rate of the cement grout should be controlled to ensure proper penetration into the ground, complete filling of voids, and adequate contact with the surrounding soil or rock.
Setting Time: The setting time of the cement grout is an important consideration to allow sufficient time for injection, expansion, and proper sealing of voids or fractures.
Quality Control: Quality control measures, such as monitoring grout properties, testing compressive strength, and conducting permeability tests, should be implemented to ensure the effectiveness and consistency of the grouting process.

Types:

Different types of cement grouting can be used in tunneling and underground structures, including:

Pressure Grouting: Pressure grouting involves injecting cement grout under pressure to ensure thorough penetration and filling of voids, fractures, or gaps in the ground.
Compaction Grouting: Compaction grouting is used to densify and stabilize loose or soft ground by injecting low-slump, high-strength cement grout at high pressures to compact the surrounding soil.
Permeation Grouting: Permeation grouting, also known as consolidation grouting, is used to improve the strength and reduce the permeability of soil or rock formations by injecting low-viscosity cement grout into the ground. Usually, the depth of the holes to be drilled which determine the depth of the rock to be grouted should be between 0.75 D and D (D is the finished diameter of the tunnel)
Curtain Grouting: Curtain grouting refers to the creation of a continuous barrier by injecting cement grout to control groundwater flow and create a watertight zone around the tunnel or underground structure.

IS 5878-7 (1972): Code of practice for construction of tunnels conveying water, Part 7: Grouting, gives recommendations regarding the pressure grouting for tunnels primarily using cement with or without suitable admixtures. The suitable maximum pressure for backfill grouting is 5 kg/cm2. In general, a maximum pressure of 7.0 kg/em2 is suggested for consolidation grouting; however, in exceptional circumstances, this pressure may be increased to 20.0 kg/cm2, given that there is appropriate cover and there is little chance of the rock joints opening up due to this pressure.

The selection of the appropriate cement grouting technique and specifications depends on factors such as the specific ground conditions, project requirements, and desired outcomes.