The trenchless renewal methods and innovations in construction is still developing. The trenchless renewal method helps in providing facilities like replacement, rehabilitation, renovation or upgradation.
Collectively we regard it as renewal method, where a new life is given to an already existing pipeline systems. When no work is conducted to increase the design life of a utility system, we call that process as a repair.
- Types of Trenchless Renewal Methods
- Selection of Trenchless Renewal Methods
- Process of Different Types of Trenchless Renewal Methods
- 1. Cured-in-Place Pipe
- 2. Underground Coatings and Linings (UCL)
- 3. Sliplining (SL) Method of Trenchless Renewal
- 4. Modified Sliplining (MSL)
- 5. In line Replacement (ILR)
- 6. Close Fit Pipe (CFP)
- 7. Point Source Repair (PSR) Method
- 8. Thermoformed Pipe (ThP)
- 9. Lateral Trenchless Renewal Methods
- 10. Sewer Manhole Renewal (SMR)
Types of Trenchless Renewal MethodsThe renewal methods can be classified into several methods as shown in the flow chart-1.
Flow Chart-1: Types of Trenchless Renewal Methods
Selection of Trenchless Renewal MethodsThe existing physical conditions of the pipeline system has a role in the renewal method chosen to perform a particular work. The conditions are type, size, material, length of pipelines or the number of manholes, service connections and bends. Other conditions are the problems faced. It may be exfiltration or infiltration, misalignment, settlement of the joint, abrasion problems, or corrosion damage and so on. Other conditions involve the methods applicability, construction difficulties, cost consideration and durability of the pipe system.
Process of Different Types of Trenchless Renewal MethodsA brief idea on each renewal method is explained in the following sections:
1. Cured-in-Place PipeThe method involves insertion of a tube made of fabric into an existing pipeline which has to be renewed. The insertion takes place either by means of water or by winching or by air inversion. The fabric has a peculiarity of being resin saturated. This enables filling of cracks, repairing the gaps by moving through the pipe defects. The Cured in place pipe method can be employed both for structural as well as non-structural purposes. The CIPP possess a higher strength that it behaves as a system which alone can sustain the whole pipeline system. The CIPP uses impregnated polyester resin or so called ERC fibre glass, that have high corrosion resistance.
Fig.1: Cure in place pipe arrangement
2. Underground Coatings and Linings (UCL)The mortar or resin can be used to fill up the lining or as coatings by spraying in trenchless renewal methods. These linings and coating would provide higher resistance against moisture and thus corrosion in pipes, where workers are not permitted. They do not have any role in increasing the structural integrity or curing the leaks or joints. The material used for this purpose may be a composition of either polyester, polyurethane, vinyl ester, concrete sealers, silicone. These are sprayed by means of a remote-controlled sprayer which are portable and travelling type. The figure below shows a lining process done by UCL method in a pipe where workers can enter. The characteristics of underground linings and coatings are given in table-1.
Fig.2: Underground Coatings and Linings Method of Lining
Table.1: Characteristics of Underground Linings and Coatings Method
3. Sliplining (SL) Method of Trenchless RenewalThis method is one of the oldest trenchless renewal method which goes for rehabilitation facility. This method can be used to help the system to restore its structural stability. We do not use this method if the system has any kind of settlement at the joints or any misalignments. The procedure in Sliplining is the insertion a new pipeline of smaller diameter into the existing one. There is gap created between the pipelines, that is filled by means of grout. The method is very cheap and gain very much simplicity. The main characteristics of Sliplining is given in table-2. The method does not gain extra hydraulic capacity.
Table-2: Characteristics of Sliplining
Fig.3: A real time Sliplining method
4. Modified Sliplining (MSL)Here pipe sections of almost close fit is inserted into the existing pipeline system. The annular space is filled by grouting. The MSL method have three variations possible:
Panel Lining (PL)This method of modified Sliplining is mainly employed for pipeline that have a diameter greater than 48 inches. This method is a renewal method, that completely provides a new design life for the pipeline system. The method has the advantage of taking different shapes. It can take non-circular cross sections also. The main type of pipe fibre used are fibre glass material ones.
Spiral WoundThe spiral wound method make use of grout and layered composite PVC to renew the existing pipe. The ribbed texture of the PVC and the grout when combine with the existing pipe, together creates a strong integrated structure.
Formed in Place pipeThe diameters ranging from 8 to 12 inches are renewed by this method. Mainly this is applied in utilities of wastewater, storm water as well as culverts. The main characteristics of MSL method is shown in table 3.
Table-3: Characteristics of Modified Sliplining Method
5. In line Replacement (ILR)The problem of pipeline systems relating to its capacity can be solved by in line replacement methods. There are three stages that represents in line replacement:
a. Pipe BurstingThis stage involves the breaking of the old pipe by means of a hammer. A new pipe is pulled and placed on the position at the same time. There are several methods within pipe bursting. They are Pneumatic Pipe bursting which make use of pneumatic hammer to break the already existing pipe. The second is static pipe bursting, where a pulling machine is employed to remove the pipe. This is employed when the old pipe is very much ductile in nature. The method does not create any noise as in pneumatic bursting. Wherever the need of brute force is necessary, we can go for this method. The third method is hydraulic pipe bursting, where the bursting head articulates thus creating burst. This method is also noise free.
b. Pipe InsertionThe pipe insertion method is also called as pipe expansion method. This method involves the insertion of a new pipe into the existing pipe. Mostly the pipe used are of clay or ductile iron.
c. Pipe removalThe method is also called as pipe eating. This method involves the complete destruction of old pipe and it is taken out in the form of a slurry. This is done by means of a HDD rig or an MT Machine. The table 5 shows the main characteristics of pipe bursting method.
Table.5: Characteristics of Pipe Bursting Method
Fig.4: The representation of insertion of a pipe bursting tool to perform bursting of a pipeline by in line replacement.
6. Close Fit Pipe (CFP)This method initially reduces its diameter temporarily and is been inserted into the already existing pipeline. Once completely entered, the diameter is regained, so that a close fit is made with the old pipeline system. The method is employed for both structural as well as non-structural purposes. The pipe used for lining is deformed to a reduced diameter by means of heat or pressure. The close fit pipe itself have two version s for structural and non-structural purposes. The table-6 shows the characteristics of the close fit pipe. Figure below shows a close fit renewal method for non-structural purpose.
Fig.5: A close fit pipe going through diameter reduction
Table-6: Characteristics of The Close Fit Pipe
The three different types of close fitting pipes that are available are:1. Deformed Pipe This pipe is inserted into the host pipe by folding. This close fit pipe techniques enables large diameter reductions say up to 50%. This can be either factory folded or site folded. 2. Die Drawing This was the first close fit lining system developed in 1980s. here the lining must undergo reduction in the diameter by means of heating at a temperature of about 100 degree Celsius. The liner is inserted into the pipe by means of the winch. Once it takes its place, the winch force is released and the liner is reverted to its original shape. This method is a continuous process. Once started it must be finished. Any problem of maintaining the winch force would make the liner to revert in a wrong location. 3. Roll Down This method involves permanent semi- reduction of liner diameter before entering the host pipe. A set of hemispherical rollers are used to reduce the diameter. A reduction of 10% is done. This permanent reduction is compromised by an increase in wall thickness. The application of pressurised cold water reverts the liner to the original dimension. This method is less suitable for liners with thinner walls. When compared to other method the winch loads used here is very less.
7. Point Source Repair (PSR) MethodThere are higher chances for local defects to be found in structurally active pipelines. Under such situations, a point source or localized repair would be found suitable. Defects with diameter ranging from 4 to 24 inches can be sealed by means of resin. These are sprayed by means of specialised machines that are available widely. The method mainly encounters with 4 problems. They are:
- The loose structural part of the masonry must be maintained
- Provide structural capacity locally. So, that it assists the damaged pipes and will be able to sustain the loads.
- To provide seal to avoid infiltration and exfiltration
- Replacement od pipe sections that are missing
Fig.6: Localized source repair- sealingThe stopping of leakage can be reduced by injecting or forcing the grout into the defective joint under huge pressure. This is a better method than lining alone. The method of chemical grouting that is applied from the surface will seal the leak efficiently. This method also helps in stabilizing the soil that is surrounding the pipe. The soil around the pipe if contains any voids or stability problems, chemical grouting works best. Fill and seal is another method of grouting, which is done in a continuous operation. Here the sealing starts from one end and continues till the end of pipe. In between the fillings are done.
8. Thermoformed Pipe (ThP)These are widely used technology in North America. Mainly employed in areas with pipelines of very small cross sections. The pipe is folded and inserted to the existing pipe. It later thermoforms to develop to the required dimensions of the host pipes. The PVC or PE pipes are commonly used for this method. These pipes have lost performance and structural capacity. They also possess a great characteristic in chemical and abrasion resistance also. The main characteristics of the method is shown in table-7.
Table-7: Characteristics of Thermoformed Pipe
- Deformed and reformed pipelines
- Fold and form Pipe liners
9. Lateral Trenchless Renewal MethodsThe methods mentioned above like close fit pipe, pipe bursting, spray on lining and chemical grouting techniques can be used to solve the problems arising in the lateral service systems. The main characteristics of lateral renewal is given in table 8.
Table.8: Characteristics of Lateral Renewal
10. Sewer Manhole Renewal (SMR)To avoid surface water inflow and ground water infiltration it is necessary to have proper manhole maintenance through its renewal. This would result in avoiding the structural damage and materials against corrosion. There is situation when the renewal process is not economical or it is better to go for manhole replacement than a renewal. The physical characteristics of the structure, age, type and condition of the site and the manhole system must analyzed before choosing a method. The main characteristics of sewer manhole renewal is given in table-9.
Table.9: Characteristics of Sewer Manhole Renewal