Williamson County has completed repairs to Cambria Drive and the road reopened on Monday, October 15.
Background: On February 8, 2018, a cave under Cambria Drive was discovered when the cave roof collapsed, and a water pipe was broken affecting water service to nearby homes. The cave starts at approximately the middle of the roadway 20 feet west of the curb and heads east approximately 200 feet and north approximately 45 feet. The cave has five chambers. The height of the cave varies reaching a height of approximately 22 feet near the entrance down to only three feet high in the fourth chamber and lower level of the fifth chamber.
The County approved a contract with Chasco in the amount of $530,425 for mitigation services for Cambria Cavern, including rebuilding the road and replacing utilities. The contract has a 100-day schedule for final completion from the date of notice to proceed on July 23, 2018 (weather permitting). During construction, additional security measures are in place including 24-hour security and additional fencing. We appreciate the neighborhoods continued patience while the road is closed, and their assistance in keeping the area safe by respecting the barricades.
Williamson County submitted an amendment to the previously approved Encountered Feature Mitigation Plan for the cave on Cambria Drive to the Texas Commission on Environmental Quality (TCEQ) after an additional chamber with two levels was discovered on August 1. The approved plan included boring two holes from the road surface into the upper level and lower level of the fifth chamber and filling both with flowable concrete. This plan provided stability for the roadway and utilities as well as protected the aquifer from potential contamination associated with utility reconstruction.
Williamson County’s contractor Chasco Constructors was working Friday morning, September 14, to reinstall the gas line under Cambria Drive when they viewed an opening while trenching for the gas line in an area that had not been previously exposed and had not been filled with concrete. Chasco immediately stopped work and contacted Cambrian Environmental who viewed the feature and called the Texas Commission on Environmental Quality (TCEQ). The opening is toward Ephraim Road approximately where the sidewalk had been along Cambria Drive. Prior to the discovery, the fracture had not been observed during any other field investigations. There is no evidence of previous human entry. The fracture is located on both sides of the trench wall and measures approximately 23 feet long with an average crack width of 6 inches. The approved mitigation plan includes having the fracture and the trench backfilled with concrete.
Williamson County received approval from the Texas Commission on Environmental Quality (TCEQ) for remediation efforts for the additional feature discovered at Cambria Cavern on September 14, 2018. The additional feature has been filled, and the Atmos gas line has been restored. Now, Williamson County’s contractor, Chasco Constructors, will begin the work of repairing the roadway. Williamson County anticipates that work will begin the first week in October. Although there have been some delays, the County anticipates being able to complete the road work and reopen the road by the end of October, weather permitting.
Neighbors to the cave on Cambria Drive can get a glimpse of what it looks like beneath the ground. In May, engineers conducted 3-D mapping of the cave with a Trimble SX10 scanner for Williamson County. That imagery is available through a link below. While manual measurements can provide a handful of data points to measure distances, this system captures thousands of LiDAR data points providing highly accurate measurements. Georeferenced panoramic imagery of the results offers an enhanced view of the cave that few people would be able to see otherwise. The Trimble SX10 scanner was only able to map the first two chambers due to the limited access to and space inside the other chambers.
The Trimble Clarity Link shows an inside image of the cave. The link must be copied into a FireFox, Edge or Chrome browsers. It will not open if you click on the link in Internet Explorer. Once placed into a browser, it may take a few seconds to load completely. If you do not see a split screen with a visual of the cave on top and a white map with red dots on the bottom, then it is not opening correctly and another browser should be tried. Once it is open, select a red dot on the bottom half of the screen as your vantage point or setup. Pan side to side and up and down in the upper half of the screen to look around. There are three setups around the column in the larger room, and one setup inside the small room.
Link https://app.trimbleclarity.com/Skybox?fileid=ZW7iHwiX-nE®ion=northAmerica&stoken=jZji66DYhtIAb_fDwsX0k2x3LAOgsyghhuvz_E0Bi6eRIASQw0U7yUfIzkaGMem1