Engineering Assessment of Damaged 66 Inch Water Main

The City of Houston maintains hundreds of miles of large diameter water transmission lines, many of which are the main source of water to vast service areas. In the unforeseen event that a vital section of the hundreds of miles of the water line is damaged and requires immediate repair, there are several considerations to recognize in providing the proper repair recommendations as expeditiously as possible. This paper presents a single challenging incident of an existing 66-inch steel water main in a tunnel section that was damaged during 20-inch x 20-inch concrete pile driving construction activities, not associated with the water line. As a result of a direct impact and potential damage to the 66-inch water main, it was important to first immediately notify the entities involved to help recognize the importance of maintaining service to vital costumers. Once the importance of this water line remaining in service was identified, immediate coordination with all entities involved was initiated to discuss the scope of work needed to expose the water main to assess the potential damage. Due to the importance of this water main remaining in operation, several options were evaluated to assess the damage potentially caused without having to isolate the water main and terminating the distribution of water. All entities directly involved agreed the most viable option was to carefully excavate the location in conflict in order to better assess the damage and evaluate the recommended repairs. The location in conflict was part of a 1,104 linear foot ring beam and steel channel laggings tunnel section constructed under state highways and underneath a detention facility. This location of the potential damage presented possible issues and construction constraints. Additionally, the unknown condition of the 66-inch water main had to be taken into account prior to any excavation to expose the area; therefore, simply providing recommendation in excavating to observe the potential damage was a challenge. Once the damage to the 66-inch water main was assessed and it was identified that the water main can remain in operation, final repair recommendations were provided and performed. In understanding the damage, immediate repairs were performed and long term recommendations were provided.