A term like sewer rehabilitation brings with it thoughts of dug up roads and sidewalks, piled up rubble, unpleasant smells, excess cost and wasted days. Traditional sewer rehabilitation work for independent houses often also meant digging up the driveway, spoiling immaculate gardens and backyards, and sometimes even removing the tiles within the house. Thanks to trenchless rehabilitation techniques, it is now become easier, cleaner, faster and cheaper to get pipes checked, cleaned, replaced, repaired and reinforced. Since trenchless technology does not require opening up the location of the target pipe, there is no mess, no smell and there are no traffic jams.
Different Methods of Trenchless Rehabilitation
There are different methods that are adopted to repair or replace pipes using trenchless rehabilitation techniques. A brief look into each will give an idea of how far we have come from the traditional open cut methods of repair. Not only are the methods intelligently designed, they are easy and cheap.
Known as the oldest method of trenchless rehabilitation, sliplining it is as simple as it sounds. The method involves slipping a smaller diameter pipe within the larger damaged pipe and sealing the annular space. high-density polyethylene (HDPE), fiberglass reinforced pipe (FRP), cast iron (CI), and PVC are the materials favored for this method. A drawback of this method is that the new pipe reduces the flow that the original pipe had. This method has now been largely replaced by the cured-in-place pipe method where the defective pipes are first identified after which either continuous or segmented replacement pipes are inserted. The new pipe is pulled in between two strategic points untill the pipe is in the correct segment. Once placed, the ends on both sides are grouted and sealed. This method is used on gravity sewers, highway and drainage culverts, outfall lines, force mains, water mains, etc. to prevent infiltration into surrounding soil and to restore structural integrity of the pipe.
Cured-in-place pipe is a sturdy liner placed inside a pipe rather than a pipe within a pipe. The main advantage of this method is that the flow rate of the original pipe is not affected. The liner is made of fiber-reinforced fabric or non-woven polyester and is designed to withstand soil, groundwater, and surface pressure and to fit into the host pipe on expansion. Using this method, the target pipe is first cleaned of debris and residues. The liner, which is impregnated with a resin, is then inverted within the pipe by applying air or water pressure. As the liner inflates with water or compressed air, it forms a close fit within the host pipe. Heat is applied to accelerate the curing process. The liner is sealed flush at the pipe ends.
This method is used for sewers, storm water drains, pressure pipelines carrying effluents, etc., to reinforce structurally unsound and leaking pipelines without having to remove the old pipe.
Using this method, a bursting head of conical shape slightly larger than the pipe is inserted into the target pipe. As the head progresses, it shatters the host pipe and pushes the pieces into the surrounding soil while creating a space for the new pipe, which is simultaneously pulled-in behind the bursting head.
This method is used to replace old pipes that can no longer be repaired by methods like lining, and spot repair.
There are two types of thermoformed pipe liners, namely deformed and reshaped pipelines, and fold and form pipe liners. This method involves inserting folded PVC or PE pipes, which then thermoforms to the desired dimension of the host pipe. The pipes are capable of temporarily altering the cross section into H, U or C-shape, and are inserted using a winch cable. Steam is applied to the pipe, the heat from which helps it to thermoform it into the required shape of the old pipe.
This method is particularly useful in repairing pipes with small cross sections. The material used for thermoforming pipes is structurally stable, has a long life and is resistant to abrasion and chemicals.
Mechanical Spot Repair
Mechanical spot repair is used to rectify pipes that have been damaged at certain points but these damages have not compromised the structural stability of the pipe. A grouting sleeve is prepared, having a mechanical locking system and a core of stainless steel. The core is surrounded by limiting straps and a foam gasket impregnated with grout. This is inserted into the host pipe and is guided to the damaged area using a CCTV camera. The sleeve is expanded using air until the locks engage, after which the air plug is deflated and withdrawn. The grout expands until the annular spaces and cracks are filled.
This method is used to restore a damaged section of pipe, and also, to repair and seal a pipe before it is lined. It can also be used to repair leaking or offset joints.
The grout-in-place pipe method involves in situ grouting between the old pipe and the new HDPE or PE lining fabrics inserted into the damaged section. A cable winch is used to pull in a pre-determined length of hose into the damaged pipe. The hose is equipped with studs on the outer side that creates an annular space between itself and the host pipe. The space is then filled with injection grouting and allowed to set.
This method is used to create a pipe within a damaged pipe section that is allowing groundwater to seep through or is releasing effluent into the surrounding soil. This method effectively fills in all gaps and cracks in the old pipe as well.
Shotcrete is basically concrete shot into place using a high pressure nozzle on a pneumatic hose called shotcrete equipment. The repair spot is reinforced using steel rods or mesh. The pipe to be shotcreted is inspected for damage by corrosion and aging. The section is subjected to pressure tests, and if pressure loss is detected, the pipe is put to use 7 days after rehabilitation. The section of pipeline is coated with a special cement lining that has additives which are able to form a good grip on the insides of the pipe and is able to withstand temperature variations.
This method is great for repairing spot leaks and cracks within the pipe, and pipes damaged by corrosion.
As many problems as may arise in the sewarage system, there are an equal number of trenchless rehabilitation methods to deal with them. With advanced machinery, innovative methods and superior material, it is becoming easier to repair or replace pipelines in crowded commercial and peaceful residential areas with minimum to null excavation, and disruption to the daily life of the common public. With increasing knowledge of the advantages of trenchless rehabilitation, more developers and landowners are opting for these methods rather than the conventional dig and replace methods.