When we receive a phone call about a cave-in, we ask the caller several questions to determine the location and public safety risk caused by the cave-in. If the reported cave-in is large and within the right-of-way, we will request that the stormwater crews fill the cave-in immediately without doing a field investigation. Otherwise, we conduct a field investigation and dispatch a work request to Stormwater to perform a first-stage repair. A first-stage repair is done by digging down into the hole, placing filter fabric in the hole, and backfilling with stone and/or soil to create a level surface. If the cave-in re-appears, we ask that the citizens call the Call Center (757-382-CITY) to report it. We will generally refill a cave-in at least twice before adding it to the list for cave-in repair. We do this to ensure that further settlement is not the result of the fill material settling.
In general, cave-ins that are less than four feet deep and not in difficult-to-reach locations are repaired by City crews. If the cave-in is large, located in a high-traffic area, or under a building foundation, it is placed on the contractor's list.
Cave-ins are repaired by several methods:
- Exposing and wrapping the failing joint with filter fabric
- Grouting the joints from inside the pipe
- Slip-lining a section of pipe
- Repair or replace the pipe or drainage structure
We often run a pipeline video camera through the sections of the pipe where cave-ins are observed to determine the extent and cause of the pipe failure. In many areas with older stormwater piping, we find that multiple joints within a section of pipe have cave-ins. For this situation, slip lining or pipe replacement is often the most cost-effective repair method. If only a few joints have failed, excavating around the leaking joints and wrapping them with filter fabric, or pressure grouting the joint from within the pipe, are the preferred repair methods. The filter fabric prevents soil from being carried into the pipe by groundwater flowing into the leaking pipe section.