As job opportunities bring in more people into our cities, the requirement for better infrastructure has become essential to prevent overuse or collapse of existing infrastructure that has been designed for lower loads. Many structures above and beneath the surface have failed because they were used beyond their designed capacities. Today, this development of infrastructure can be witnessed everywhere. However; hidden beneath our feet is a network of conduits such as those carrying electric wires, TV and telephone cables, and pipelines carrying potable water and sewer waste that is growing horizontally.
Trenchless rehabilitation has made it rehabilitating these pipes easier and more effective, with better results in a lot lesser time than what the traditional dig and replace methods required. Sliplining and pipe bursting are two such trenchless rehabilitation methods that have made repairing pipelines easier while also increasing its effective lifespan. Depending on the type of damage to the pipeline, either of these methods explained below are adopted.
Sliplining is a simple procedure that is used to rehabilitate pipes that are leaking or have lost their structural stability to an extent. Typically, sliplining is ideal for straight pipes with slight to no bends, no protrusions or severe deformations, and can be done either continuously or in segments.
The host pipe is first inspected using a CCTV camera and cleaned of debris. The liner is selected such that the outside diameter of the liner is 5% to 10% less than the inside diameter of the host pipe depending on the size of the pipe. This difference is maintained to ensure a smooth insertion process and to maintain maximum flow capacity of the host pipe. The lining materials used for this procedure are high density polyethylene (HDPE), polyethylene (PE) or polyvinyl chloride (PVC). To insert the liner, a manhole is usually sufficient unless circumstances require the excavation of a pit. The required length of the liner is winched into the host pipe from the entry point to the exit manhole. Segmented sliplining is employed when glass reinforced plastic (GRP) pipes are used and can be winched or pushed by hydraulic force into the host pipe. The annular space between the new liner pipe and the host pipe is filled with grout. Depending on the purpose the grout will accomplish, the grout strength is selected. For example, low strength grout is used if the purpose is only as filler for restraining the pipe while high strength structural grout is used when the liner has to be linked to the host pipe. After the required curing period of 24 hours, laterals and other service connections can be added.
The sliplining method of trenchless rehabilitation restores the structural integrity of the host pipe, improves flow coefficient, eliminates the problem of corrosion, minimizes or eliminates inflow/infiltration (I/I) into the pipeline, is cost effective and time saving, requires little to no excavation for insertion and can be done from a manhole. However; sliplining reduces the internal diameter of the host pipe, thus reducing the pipeline volume. It requires straight lengths of pipes for effective installation and cannot be used for excessively deteriorated pipes or through pipes having bends and elbows.
Pipe Bursting for Pipe Repair
Pipe bursting is used to replace old brittle pipelines that are non-serviceable, or to install larger pipes to increase flow capacity. Pipe bursting utilizes the simple principle of installing a new pipe while bursting the old pipe into fragments using a bursting head.
Utilizing the pipe bursting method depends on various factors such as soil type, material of the host pipe, burst length and upsize diameter. The process of pipe bursting utilizes a bursting head usually conical in shape with a diameter 50-mm to 100-mm larger than the new pipe. The bursting head is inserted into the host pipe and pulled through. As the bursting head progresses, it causes a radial expansion of the host pipe which exceeds the tensile and shear strength of the host pipe, resulting in splitting of the pipe or fragmentation. The fragmented pieces are pushed into the surrounding soil, and the resulting annulus creates sufficient space for the new pipe to be pulled in. The new pipe is attached to the rear end of the bursting head and is simultaneously installed as the bursting head progresses and fragments the host pipe. Some of the materials used for replacing pipes using the pipe bursting method include HDPE and PE. The space between the new pipe and the adjacent pipe is sealed with a suitable material.
One of the main advantages of using the pipe bursting method of trenchless rehabilitation is the fact that larger diameter pipes can be installed to increase the flow capacity. Replacing old pipes using this method is swift and cost-effective, as the host pipe need not be removed but is fragmented and embedded into the surrounding soil. However; pipe bursting does not allow for change of slope, requires bypass pumping during the process, cannot burst through valves and may cause surface heaving under unfavorable soil conditions.
Pipes may have to be rehabilitated for a multitude of purposes. Some pipelines require upsizing the pipe diameter to accommodate an increase in load that it may have to carry in addition to the designed load, and it may require replacement with larger diameter pipes. Some pipes are old, corroded and leaking and require repair or replacement.
There are many vitrified clay pipes (VCP), concrete pipes, cast iron (CI) pipes that have served their purpose for decades or some even over a century. Many of these pipes are in good working condition with some sections that need to be replaced or repaired. Replacing an entire pipeline length may prove to be very expensive and highly disruptive. Sliplining and pipe bursting are ideal methods for replacing such pipe sections quickly and effectively. With pipe materials like HDPE, PVC, GRP and PE trending in the trenchless market, owing to their superior properties like corrosion and chemical resistance, flexibility and stronger, leak-proof joints, the replaced sections of pipe provide structural integrity, low maintenance and longevity to the pipeline.