By Sara Heger, Ph.D.
Proper pipe cutting is critical to ensure that a watertight seal is created between pipes and fittings.
The following is the recommended procedure for pipe cutting:
- Prepare: Examine the pipe to ensure that it is not damaged with cracks, gouges, dirt and abrasion. If the pipe end is imperfect, cut it back to expose good material. Discard a damaged fitting. The pipe and fittings should be at the same temperature to ensure a proper joint between the two components.
- Cut: The pipe must be cut square at the end using a PVC pipe cutter, hand or chop saw. Make sure that the end of the pipe diameter is not compromised and remains circular.
- Deburr: Cutting PVC pipe nearly always creates burrs on both the inside and outside edges of the pipe. Make sure all burrs from cutting are removed with a file, knife or other deburring tool on both the outer and inner surface of the pipe end. If burrs are left on the end, they will scrape cement from the inside of the fitting as it is being pushed in, resulting in a non-watertight seal. Burrs on the inside pipe surface can snag hair or other debris, plugging up the pipe. With gloves on, run your fingers around both edges to feel for any burrs that might have been missed. Before connecting the cut-end, bevel the end 10 to 15 degrees with a file or reamer. This prevents cement from being pushed aside by the square ends of the pipe cut.
When using pipes with spigot and bell ends, the pipes should be arranged such that water flows from the bell end to the spigot end of the pipe. Therefore, the glued connection will have the spigot end entering the bell end. The spigot end should be properly beveled to have a flush connection between the spigot end and bell end. This avoids a lip that can catch material.
When multiple pipes are running in the same trench or into a component, the installer should label the pipes with either a permanent marker or with a stamp to aid in future troubleshooting. It is recommended to place a marking every 20 feet and at any location where a portion of the pipe or clean-out is visible.
When piping needs to be installed in areas near a septic tank or advanced treatment unit excavation, it is best if the pipe is supported by undisturbed soil instead of running it across the top of the tank or unit. Trenches need to be dug and prepared in a way that the pipe is protected from damage. Trench bottoms should be free of rocks and debris and provide uniform support. If there is bedrock, hardpan or large rocks on the trench bottom, the trench should be bedded. Particularly on long runs with small-diameter pipe, the trench width should be wide enough to allow the pipe to be snaked from side to side and at least twice the pipe diameter. Where multiple lines of pipe are installed in the same trench, they should be spaced far enough apart to permit thorough tamping of backfill between adjacent lines with a minimum of 0.5 times the nominal pipe diameter apart.
Bedding material and its placement is of critical importance to installation and performance. It is essential that native and imported materials are properly classified for use in bedding. Many jurisdictions have their own bedding specifications that call for special material to completely cover the pipe; care must be taken to meet these requirements.
Soil to be used as bedding in the pipe zone must be appropriately compacted. When selecting embedment materials, make sure that native soil migration from the trench walls cannot occur. A well graded, compacted granular material prevents this. In trenches subject to groundwater inundation, the granular material should be compacted.
The trench bottom should be dry. Surface water draining towards the trench must be redirected. Installation of piping is much more difficult if water is in the trench due to the tendency for pipe flotation; therefore, dewatering is required to minimize these issues and the likelihood of instability of trench walls and slopes. Groundwater should not be permitted to rise above the trench bottom until after the installed pipe is fully bedded and enough fill is in place to prevent flotation.
The soil layers
- The foundation is the underlying natural soil material. The bedding material is usually less than 6 inches thick and provides continuous support of the pipe and underside of the pipe. If a coarse, granular material is used for bedding the pipe, it should also be used up to the midpoint of the pipe. Otherwise, side support may be lost due to the migration of finer material into the bedding.
- The next layer is the haunching that comes from the top of the bedding to about halfway up the pipe diameter (springline) and is a strong factor in controlling pipe performance and deflection. Proper selection of haunching material is essential to the PVC pipes’ ability to support vertical loads. It is frequently a special material with sizes not exceeding 3/4 inch. The haunching procedure is to tamp the embedment materials under the haunches and around the pipe to the midline of the pipe to provide effective support.
- Following haunching, initial backfill is applied, followed by final backfill.
Locator lines may be placed in the pipe trench to help locate and identify piping for future maintenance. Tracer lines can be as simple as iron wire that can be located with a metal detector.