Injection grouting

 

When underground spaces are needed for utility, services and storage, in addition to parking and other uses such as recreation or amenity space, structural retrofitting  is one of the most cost-effective ways to expand a vadose space or create new ones. It involves injecting grout into an existing void to create a new space large enough to accommodate the proposed use. The cost of injecting grout is often less than the cost of excavating the same area again, so it can be a better value over time than conventional construction methods. Injection grouting involves pumping grout into an existing void. This creates new pore space within the soil that allows excess water to drain faster and more efficiently; sealing any leaks; and reducing air infiltration, which helps control odors, insects and microbial growth. Once injected, you can then finish with a variety of surface finishes such as paving stones or decorative brickwork.

What is grouting?

Grouting is the process of injecting a material such as cement into an existing void in order to increase the size of the void and to create new pore space within the soil. The grout should be wide enough to fill the void completely, but not so wide that it causes pitting or damage to the sides of the hole. The grout can be injected using a variety of methods, including pump-down and auger systems, pressure injection and low-volume jetting. Low-volume jetting is also known as micro-jetting or micro-jetting and uses a high-pressure jet of water mixed with grout to flush old soil from the sides of the hole, and then to flush the remainder of the void with the new grout.

How is grouting used to expand a vadose zone?

Injection grouting is used to expand existing vadose zones, or porous subsurface spaces, such as existing underground parking structures, below-grade utility structures and below-grade storage areas. It creates new pore space within the soil, which allows excess water to drain faster and more efficiently. It also seals any leaks and reduces air infiltration, which helps control odors and reduces potential for microbial growth. Once injected, you can then finish with a variety of surface finishes such as paving stones or decorative brickwork.

Advantages of injection grouting

- Greater cost-effectiveness than conventional construction methods. - Better value over time than conventional construction methods. - Inexpensive to install. - Easily reversible, if the need for the expanded space arises at a future time.

Limitations of injection grouting

- May require clean-outs and other inspection near the surface. - May require soil augmentation, including additions of polymeric sealants. - May not be suitable for certain materials, such as bore holes or certain types of soils. - It may take a few months for the pore space to fully open up. - Newer injection grout may not withstand future seismic activity.

How much does it cost?

Injection grouting costs typically range from $2,000 to $6,000 per linear foot.

Other costs of injection grouting

Labor: If the soil is relatively clean and loose, the injection of grout may require some hand work by the contractor to ensure that the material is properly injected. If the soil is dense and difficult to work with, additional labor may be required to finish the injection, such as digging a trench or digging out an obstruction. Since the grout is being flushed out of the void, any excavation would require a full backfill to fully restore the void after excavation. Equipment rental: The type of equipment used to inject the grout will vary depending on the method used. Some contractors prefer to rent equipment to keep costs down.

Summary

Injection grouting is a cost-effective way to expand a vadose space or create new ones. It involves injecting grout into an existing void to create a new space large enough to accommodate the proposed use. The cost of injecting grout is often less than the cost of excavating the same area again, so it can be a better value over time than conventional construction methods.