Underground water main conduits and/or sewage conduits that have been installed decades ago have gradually deteriorated to the point where pressurized treated water escapes through cracks and holes at rates that can reach 50%. Similarly. Sewage conduit may have become so deteriorated that a substantial amount of sewage water seeps into the environment instead of being delivered to treatment facilities before re-entering the environment.
For many years now, technologies have been developed and used to rehabilitate damaged water and sewage conduits. The various technologies basically consist of re-lining the inside walls of existing underground conduits to rehabilitate the underground conduits.
U.S. Pat. No. 5,497,807 describes a method of rehabilitating damaged conduits which consists of inserting a replacement pipe into the existing conduit and filling the gap between the new and old pipe with a filling agent. However, this technology is limited to segments of conduit that do not have side pipes or branch lines connected thereto since those would be blocked permanently. If used in conduits with multiple service entrances or branch lines, each service entrance and branch line would have to be individually reconnected to the main conduit which would require digging the ground up to drill out the rehabilitated conduit and reconnecting each branch line which is expensive and time consuming.
U.S. Pat. No. 4,951,758 describes a method of rehabilitating damaged conduits which consists of initially plugging the service entrances of the existing conduit with a water plug carrying a position marker oscillating with a predetermined resonance frequency with a plug setting robot controlled by a technician looking through a video camera connected to the plug setting robot and thereafter lining the existing conduit internally with a continuous strip of synthetic resin wound spirally and filling the gap between the new and old pipelines with a filling agent. Once the re-lining of the existing conduit is done, the water plug can be located with a detection and drilling robot using a loop antenna connected to signal processing circuits which recognise the frequency of the position marker and relay the intensity of the signal to the operator through a graphic display allowing the operator to zero in on the center of the water plug by moving the robot past the water plug until the signal diminishes in the horizontal direction and repeating the process in the radial direction. Once the center of the water plug is located, the water plug is drilled out using a drill mounted on the robot which is operated by the technician. Problems may arise when there are multiple water plugs in the same area giving rise to multiple signals. To alleviate this problem, water plugs with position marker having different resonance frequencies are used when multiple service entrances and branch lines in close proximity to each other need to be plugged.
The method described in U.S. Pat. No. 4,951,758 works reasonably well but the detection process requiring multiple passes over the position marker of the water plugs in order to zero in on the center of the water plugs is somewhat tedious and time consuming. As well, the use of water plugs with position marker having different resonance frequencies requires a selection of water plugs to be carried inside the conduit by the robot during the plug setting operation to prevent having to return above ground for water plugs with different resonance frequencies.
Therefore, there is a need for a method and apparatus for detecting and drilling plugged service entrances in a conduit after rehabilitation of the conduit which would be less time consuming and eliminate some of the drawbacks of prior art methods.