Mechanical spot repair is a simple procedure that typically does not require the sewage line to be out of commission. However, from time to time a sewer bypass is necessary to complete repairs of the pipeline.

Mechanical Spot Repair Overview

Mechanical spot repair is the correction of issues from inside the pipe. Spot repair includes repairs to cracks, breaks, infiltration, fractures, collapsed sections of pipe and offset joints. This trenchless rehabilitation method restores the integrity of the pipeline.

To complete this type of repair, workers send a machine comprised of a stainless-steel core surrounded by a foam gasket and limiting strap inside of a grouting sleeve into the pipe. Using remote operation and CCTV to monitor progress, the operator directs the equipment to the spot of disrepair. The core’s gasket inflates until the sleeve locks in place. The grout, which is pushed into the crack by the sleeve, fills the annular space and fills in the break.

When to Bypass Sewers

Typically, the bypass is unnecessary. One of the benefits of mechanical spot repair is that the line does not have to be interrupted to send the machine in. However, on rare occasions, the bypass is necessary. An example of this is for large sections of pipe, which may take multiple days to complete; in such cases, bypassing the pipeline can make the project go more smoothly.

Additionally, if the mechanical spot repair is a precursor to sliplining or using cured-in-place pipe (CIPP), bypassing the line is essential. Both sliplining and CIPP must cure before the pipeline is put back into service. Typically, installation is complete within a day, and curing is finished within a day.

Planning Sewer Bypass

Before a sewer bypass is implemented, workers should adequately plan, even if it is only going to be used for a few hours. Proper planning lessens the chance of issues during repair. (For more on sewer repairs, see The Essential Pros and Cons of Trenchless Sewer Rehabilitation.)

Peak Flow

Peak flow is the highest flow of the day. This flow is not the average sewage flow through the pipe. Typically, it occurs twice a day. The first peak is in the morning when everyone is up, getting ready for work or school and are using the restroom, taking showers, brushing teeth, etc. The other time is late afternoon to early evening when everyone is returning home from school or work.

It is essential to understand the peak flow time and rate to select the appropriate bypass pumping system.

Pipeline Depth

The depth of the pipeline affects the bypass pumping system. Sewage lines at less than 25 feet deep can rely on a non-clog above-ground pump to move waste into the new line. However, if a sewage line is deeper than 25 feet, a submersible pump is necessary.

It is important to remember that suction lifts greater than 25 ft are not practical. This impracticality is due to the flow capacity affected by deeper suction depth.

Duration

Before bypassing the sewer, you need to know how long the project is going to last. For the most part, mechanical spot repair projects are complete in less than a day. However, if there are other rehab projects occurring with the section in addition to the spot repair, it could take longer.

Knowing how long the line is to be out of commission allows planners to select the proper pumps. Some pumps are designed to run 24/7, while others need to be turned off after so many hours. Additionally, if a project requires pumps to run for longer than a day and run 24/7, an adequately trained equipment watchman is necessary.

Access Issues

Sewer bypass planning must include understanding access. While the project may take place in a remote area with plenty of room for equipment, it is highly unlikely. Public spaces can create issues for workers as they set up the bypass.

Diversion or closure of roadways may be necessary for equipment placement. Also, the presence of buildings may make it difficult to put the appropriate pumps in place.

Project managers must consider pump footprint and placement before ordering equipment. They should also adhere to any local regulations regarding permits for bypass equipment, especially if placed on private property. (Sewers are much more than just a collection of pipes. To learn more, see The Complex World of Sewer Networks.)

Pumps

With all the necessary information in hand for the project, planners can select the appropriate types of pumps. There are two types: above ground and submersible.

Above-ground pumps are used when pipeline depth is less than 25 feet. Managers can choose from a self-priming or prime-assisted option. Self-priming pumps self-prime only when they are full of water, so they must remain filled always. Generally, self-priming is only used when priming time is not critical, as they can take longer. Prime-assisted primes itself under dry conditions. These pumps prime more quickly and consist of a pump, driver and priming device.

Submersible pumps are used when the pipe depth is greater than 25 feet. These pumps are either electric or hydraulic driven. Hydraulic pumps include hydraulic hoses and motors.

Potential Issues

There can be some potential issues with bypassing a sewage line. For instance, there could be a faulty pump – this would cause problems with pumping waste out of the pipeline, making it challenging to complete the project on time.

Another issue could be friction loss in the temporary line, causing the waste to stagnate in the pipeline and not move on to the appropriate location. Therefore, redundant pipes are necessary – without one, or if there is an issue, waste removal cannot continue.

Any of these issues could cause sewage to spill into an open area. Sewage spillage is a hazard to residents in the area. It can contaminate groundwater or back up into the water supply.

Proper planning is the key to a successful sewer bypass. Once the mechanical spot repair and other associated repairs are complete, the line is put back in service.