Investigation of Existing Pipe & Site Conditions
Investigation of the old pipe condition assists in selecting the suitable rehabilitation technique and provides the exact location of the lateral connections. The conditions of the existing pipe may render pipe bursting as an unsuitable method for correcting the problem. The presence of sags in the line may require treatment for the sag prior to bursting. The host pipe (diameter, material and conditions) and the diameter of the new pipe guide the contractor to select the appropriate bursting system type, size, and accessories during the bidding and construction phase. The site conditions and surface features may affect the locations of the insertion and pulling shafts, staging area for fused pipe, traffic control planes, and footprint for the needed bursting system components.
Insertion and Pulling Shaft Requirements
When planning for shaft locations, the engineer identifies spots where excavation is needed to replace manholes, valves, lateral connections, or fittings. These excavation spots are used as insertion or pulling shafts. However, if excavation at the manhole location is not feasible or needed, shaft excavation at other locations may be considered. In selecting the location of these shafts, the engineer has to consider the following issues:
- Sufficient staging area for the fused replacement pipe to avoid blocking driveways and intersecting roads.
- The shaft length should be long enough to allow alignment of the bursting head with old line and for the PE pipe to bend safely from the entry point to the ground surface.
- Space for the construction pieces of equipment such as backhoe, loader, crane, etc.
- Nearby flow bypass discharge spot or space to lay by pass lines without blocking driveways and intersecting roads.
- Traffic control around shafts.
- Soil borings close to these shafts.
- Discharge spots for dewatering if needed.
- Using the same shaft to insert or pull pipes more than once.
Generally, the engineer recommends locations for the insertion and pulling shaft but leaves the final determination to the contractor (through a submittal process) with the guidelines of minimizing excavation and disturbance to the surrounding environment.