On Aug. 1, while crews were filling the cave, they noticed a small void in the wall of the main chamber, located approximately 10-12 feet from the ceiling of the cave. TCEQ was notified and the work was halted until Cambrian Environmental could investigate the void, which led to a crawlspace into a fifth chamber under Ephraim Drive.
The ceiling of the lower level is 20 feet below the surface, but it could have been problematic with heavy trucks on the road.
With TCEQ’s blessing, two holes were bored through Ephraim Road’s surface into the upper and lower levels of this chamber, and they were filled with flowable concrete. This protects the stability of the roadway and utilities and prevents contamination to the aquifer.
Once TCEQ received the contractor’s evaluation and determined the work could continue, crushed rocks of a specific size were placed in the main cave, so that any water that finds its way to the cave can continue to drain towards the aquifer as it has for millions of years.
Filter fabric was placed over the crushed rocks to allow water to percolate through them and into the aquifer. This prevents the concrete from filling the voids within the material.
The concrete was poured 18 inches at a time, using geogrid (a geosynthetic material used to reinforce soils) and wire retaining forms for support from ground to ceiling. This isolates the concrete to the area of the cave under Cambria Drive.
Williamson County Engineer Terron Evertson said, “Chasco is a Williamson County company that has made this project a priority for their company. Because of Chasco’s dedication to this project, and the professional team they have assigned to the project, they have delivered stages of the project ahead of schedule.”
The cave was sealed on Aug. 31. The work to re-establish utilities and rebuild sidewalks, curbs and gutters is expected to be completed in October.
The county could not fill the cave in the areas directly under the homes because it is only responsible for county property and not allowed by state law to spend tax dollars on private land.
Contingency planning is routine for our Road and Bridge department. The county budgeted $741,000 in remediation costs from an emergency fund. As for those homeowners, none have experienced foundation shifting. The homes are over 30 years old and are probably good for many more!