Options for Pipe Rehabilitation - Trenchless Categories
1. On-line Replacement
Pipe bursting or in-line expansion is the pushing out of the present pipe to give way to a slip lined pipe. This method is usually used with short sections and is allowed for larger slip lined pipes than the existing pipes. Used in this option are static wherein no movement occurs within the internal parts and dynamic characterized by pneumatic or hydraulic forces at point of impact.
2. In-Situ Renovation
In-situ techniques can follow the existing profile, minimising the bore reduction and the quantity of grout needed to fill the annular space. Many in-situ techniques rely on adhesion between the liner material and the existing pipe wall, and to ensure a rigid seal, pipe must be very clean and a present leaks need to be patched up properly.
Slip Lining is the sliding of a flexible and a smaller diameter pipe into the present pipe. The space between the old and new pipe is packed with foam, pea gravel, or others in order to continuously avoid leaks and improve structural integrity. This option needs access of ground surface to lower the discrete pipe sections called the large access pit. This option is advantageous since it can be used for almost all types of sewer pipes with the least impact on other utilities. However, the reduction of pipe diameter can also cause the loss of cross-sectional capacity.
b. Fold and Formed or rolldown
Fold and formed or rolldown is the insertion of a flexible pipe shaped in a U form into an existing pipe with the aid of chemical and mechanical forms. The liner, rounding mandrel, rounds out the present pipe is heated and pressurized to complement the shape of the host pipe. Since heat and pressure are required in order to allow for the perfect lining and pipe-fitting, the pipe should be well-cleaned and allow ample time for stabilization since the material has a high coefficient of expansion. Some advantages for this option are the minimization of damage to other buried lines, non-need for grouting, and the rehabilitation of very corroded pipes. Materials to be used range from high tensile polyester reinforced polyethylene to HDPE, PE, and PVC.
c. Cured In Place Pipe (CIPP)
Cured In Place Pipe or CIPP is the insertion of a flexible liner like felt which is infused with thermosetting resins via the manholes into the pipe. Contact with steam or hot water solidifies the resin. Insertion is done either by winch in place or invert in place techniques. This option needs no added digging and is helpful in pipes that need minor structural strengthening. It can be used on misaligned joints, offsets, bends, and non-circular pipes. Materials that can be used are textiles specifically polyester fiber felt and resins such as unsaturated polyester (poly-urethane), vinyl ester, and fiberglass epoxy. The main advantage of this technique is the speed in which the installation is undertaken without any required excavation. However, preparation is intense requiring extensive surveying, cleaning, by-pass pumping, and pre-grouting when necessary.
Coating is the use of a material as a complete restoration or patch to the existing pipe by application via a roller, trowel, or spray. This method is applicable in a dry clean surface and requires no loose material in sewer. Treatment takes about an hour after application of the material. Products that can be used are vinylester, urethane, silicone, polyester, shotcrete, and epoxy. There are two types of coating namely, structural spray-on linings that use reinforced mortar and non-structural spray-on linings that utilize epoxies and cement mortar.
Ferro-cement easily links connections and can simply allow for diameter changes and noncircular sections. It can be utilized in partial flows incorporating precast invert flows. Designing for pressure line is possible and reduction of cross-sectional capacity is kept to a minimum. Work can be undertaken from extant manholes and design for pressure line rejuvenation is possible. However, the technique is still at its infancy and requires well-experienced and skilled operators. Difficulties may be experienced during spraying while preliminary sealing may be needed to prevent infiltration.
Cement Mortar Pipe or Grouting is a method using cement mortar inside a pipe line to keep it from deterioration or slip line cement pipe into sewer. Application of cement mortar coating can be done on iron pipes, steel, or concrete. Done by hand or via an automated spreading machine, the coating is composed of one part sulfate resistant cement to two parts sand which can stretch the pipe's service life up to 50 years. This method is not applicable in pipe networks with many bends and also in very cold areas. Options to be used are HOBAS pipe such as glass reinforced polymer mortar (CCFRPM), polymer mortar, and glass reinforced cement.
g. In-situ Liners/Modified Cross Sectional Liners
In-situ Liners/Modified Cross Sectional Liners is a technique whereby a soft liner is inserted with a polyester laminate supported by glass. Pulling is achieved via the defective drain run with water or air pressure utilized to mold it in place. This method requires pipe cleaning and plugging of extant leaks and can only be used in pipes bigger than 48 inches. Options include geo-membrane panels or HPDE which needs anchor studs, geo-membrane panels (HPDE) that require access pits, and preformed strips (PVC) that make use of strips. The first and the third use grout as structural support while the second utilizes anchor bolts for sewer attachment.
h. Grouting sleeve
Grouting sleeve is a type of CIPP wherein the pipe at a decreased diameter is driven down the pipe and enlarged in place. Grout enlarges and goes through the cracks with the stainless steel core finalizing the rehabilitation.
Cement Mortar Lining
When something turns old, the natural instinct is to replace it with something new. Even though that seems to be the most natural thing to do, this reasoning simply does not suffice when faced with pipe deterioration problems.
After several centuries since the first aqueducts were installed, it is in no way a stretch to say that the pipes existing today have greatly deteriorated.
Unfortunately, dealing with old, worn pipes are not as easy as dealing with old, worn shoes. Modern pipes are often buried under land where communities and/or industries have been built. Touching these pipes in any way will inevitably lead to the disturbance of said communities and/or industries. The deterioration of water mains cannot be ignored but people's lifestyles cannot be disrupted so easily. Full pipe replacement will always be preferable if the only thing to be considered is the state of the pipes but it is not the case hence alternative routes are taken.
It is in the pursuit of these alternative routes that the Cement Mortar Lining method was born in the 1840s.
The Cement Mortar Lining method is a technique that rehabilitates water mains rather than replaces them. It is mostly used on cast iron or ductile iron pipes, created using "low dig" technology that distributes drinking water, industrial water or sewage water.
The first step to the cement mortar lining method is the cleaning of the pipe. Because the pipe is filled with dirt and rust, it must be cleared before anything is applied in it. This step is crucial as it will dictate the success of the process. Should it be skipped or done haphazardly, the application of the mortar might be led askew and more harm than help might be incurred on the aging pipes.
The next step is the mortar application itself. This may be done through either of two methods: the Centrifugal lining method or the Spraying method.
In the Centrifugal lining method, mortar is evenly poured into the pipe. Afterwards, the pipe is rotated to spread the mortar in the pipe via centrifugal force. Once the mortar is compacted, the rotation is stopped and the residual water drained.
The Spraying method is a bit simpler. Before any spraying is done, the pipe is rotated. The forced rotation is then stopped to enable the spraying of mortar into the pipe as it moves in constant linear speed. Once the mortar is sprayed, the rotation of the pipe will be increased to smoothen the lining's surface.
Once the lining process is done, the curing process ensues. It is done in a dry, closed area where pipe ends may be capped so as to avoid water evaporation. After this, the pipe is reinstalled belowground and will have an extended lifetime of 30 to 50 years.
Cement mortar lining is a rehabilitation method preferred by neighborhoods as it is less disruptive and more cost effective. Once a pipe undergoes the process, its hydraulic carrying capacity improves along with the quality of water it delivers. In addition to this, the brown discoloration of the water which probably alerted the authorities of the pipe's need to be rehabilitated is reduced.
While cement mortar lining does not substitute for complete replacement and the pipe will eventually have to be replaced one day, no arrangement is everlasting and it does save the residents some trouble.