Problem: 

During construction of a deep wastewater structure for the City of Houston, excavation advanced to approximately 40 feet below grade when significant groundwater intrusion was encountered. A prior geotechnical borehole extended to approximately 80 feet, creating a direct vertical hydraulic pathway that allowed groundwater to migrate upward into the excavation.

To temporarily manage the inflow, the contractor installed a corrugated metal pipe (CMP) to approximately 15 feet depth, using it as a controlled collection point for groundwater. This system functioned as a relief pathway, allowing sump pumps to continuously remove water and establish a workable environment for construction.

This approach enabled placement of an initial working slab; however, groundwater continued to migrate through the same pathway beneath the slab. Without a permanent cutoff solution, ongoing infiltration posed a risk to slab integrity and prevented continuation of structural construction.
 

Solution: 

Following slab placement, Superior Grouting implemented a targeted polyurethane injection program utilizing NCFI-4RH (formerly 24-003), a hydrophobic structural polyurethane system whose reaction profile and expansion characteristics make it effective for groundwater control in wet subsurface conditions.

Injection was performed around the perimeter of the CMP and the identified hydraulic pathway, rather than directly into the active flow. Multi-depth injection points were used to intercept the migration zone and treat the surrounding soils.

As the polyurethane expanded, it permeated and displaced within the soil matrix and surrounding materials, reducing permeability and creating a continuous grout curtain around the CMP. This barrier effectively stopped groundwater infiltration into the structure.
 

Results:

Groundwater inflow was rapidly reduced during initial injections and fully controlled shortly thereafter. The grout curtain successfully eliminated the vertical migration pathway, preventing further intrusion beneath the slab.

With the pathway sealed, continuous pumping was no longer required, and the contractor was able to proceed with construction without delay. The solution provided both immediate groundwater control and long-term subsurface performance, supporting the successful completion of a critical municipal wastewater infrastructure project.