Where suitable internal repairs are not possible, it may be necessary to access the pipe from the surface to complete a repair, install a valve, etc., e.g. in the case for water or gas mains providing service to property owners along a public right-of-way.
Potholing / Keyholing
Potholing or keyholing is a method of accessing underground infrastructure with minimal excavation, disruption of services, traffic and pedestrians, and reinstatement. The small, narrow, vertical excavations are precisely controlled. It usually involves coring the existing surface, excavating using vacuum equipment, performing the required work, then backfilling and reinstating the core. The typical purposes are for locating, inspecting, repairing, maintaining or modifying existing infrastructure or installing new lateral service connections to properties. The operations are performed from the surface using specialised long handled tools, avoiding the need to have workers in excavations. This method of excavation is commonly referred to as “soft excavation” and is commonly accepted as being equivalent to hand digging around underground facilities.
Potholing or keyholing technologies allows workers to cost-effectively expose and perform work on underground pipes and other facilities without resorting to more costly and disruptive conventional excavation methods. Work is typically completed and reinstated within a day.
The terms potholing and keyholing can be considered interchangeable. Sometimes potholing is used just to refer to narrow vertical excavations and sometimes keyholing is used where operations are performed on the utility service using specialised long handled tools.
Coring
The first step in potholing or keyholing usually requires removing a section of road or pavement surfacing. This is best performed using a circular core-hole cutter. Typically, the core size is up to 600 mm diameter depending on the type of work being undertaken. The core-cutter is mounted on a stabilised vehicle and the rotating circular drum blade is slowly pushed into surface. After the core has reached the required depth, the core disc is removed and retained. For reinstatement the core is replaced in the surface hole using specialised grout. It produces a very strong and neat finish.
Vacuum Excavation
Vacuum excavation systems combine suction and pressurized jetting equipment to support a number of construction and trenchless applications. These systems come in a wide variety of sizes. They may be self-propelled or mounted on trailers. The basic components of a vacuum excavation system include a suction pump and hose to vacuum spoils from the earth to a slurry or debris tank capable of storing spoils until they are discharged off-site or as backfill, and an engine to power the system components. The system may include compressed air or water pressure jetting capabilities to loosen the soil prior to vacuuming it out of the hole. These would include water tanks, pumps, water lines, and jetting tools such as wands and water lances.
Ideally, the debris can be re-used to backfill the pothole.
Pressurised jets and vacuums may be employed to remove debris, and clean clogged utilities. During preconstruction, vacuum excavation systems may pothole to expose existing utilities where use of mechanical excavators, backhoes or boring equipment could risk damage to the utilities. During construction and post construction, vacuums may be used to remove spoils associated with directional drilling and tunneling operations. In addition, vacuums are sometimes used to support hand tunneling and auger boring operations where the vacuum hose is extended to the face of the tunnel to remove spoils from inside the casing. Jetting and vacuum features of vacuum excavation systems may also be used to create shallow trenches for the installation of cables and utility services.