1. SEWER REHABILITATION / REPLACEMENT FOR RCC PIPES WITH INTERNAL LINING
Mr. D.M.Mandalia*, Mr. Deepak Kumar Mallick**, Mr. Mohammed Junaid***
* Deputy General Manager–Civil, Infrastructure Business Unit, Matulya Office
** Engineer–Civil, Infrastructure Business Unit, Matulya Office
***Engineer–Civil, Infrastructure Business Unit, Matulya Office
Abstract: Sewer rehabilitation / replacement require expertise as the sewer lines are buried under the ground. Latest
technologies are adopted for this type of work. Sewer damage in most of the cases is due to corrosion of pipes due to
H2S gas which oxidizes to produce H2SO4 which is venerable to concrete. Sewer lining increases the resistance of the
pipes to the sulphide attack and increases the longevity of the sewers. Sewer lining are done by, spraying adhesives /
paints / mortar / polymer or by putting flexible PVC / HDPE / Rotaloc lining. Different lining types have their own
specification and characteristics. Before any lining is done proper inspection is required to know the causes and defects
occurred in the pipe line. CCTV inspection is one of the best methods adopted for inspection of sewer lines in BWSSB
project. After techno-economic analysis polyurea / high alumina Lining is recommended upto 900mm diameter and
above 900 mm PVC lining is recommended.
KEY WORDS: Rehabilitation, Replacement, Polyurea, CCTV, PVC, HDPE, High alumina, Sulphide, Corrosion,
Rotaloc, Metachem, UV, Purathane, Dyno-Rod, VOC, GRP, EAP, BWSSB, JICA.
Introduction
Life cycle management in relation to the sewerage network is of paramount importance to get the benefit of maximum
cost effective utility during its life span. Sewers remain hidden from eyesight and often neglected till there is problem
occurs due to overflow. If repairs / rehabilitation / renovation / replacement are not carried out at proper time, the
useful service life gets shortened with the risk of dangerous collapse situation.
In sewerage system, the actual asset is pipes/conduits and the manholes. The cost component of this asset is 30 to 35%
as compared to the total cost of the system. If therefore a new pipe or the equivalent can be inserted inside the old sewer
or it can be renovated without any further excavation, theoretically a saving of 65 to 70 % in traditional cost can be
considered. In view of this, only after careful inspection, if engineer decides that for a variety of possible reasons, the
existing sewer is in fact not suitable for the repairs / rehabilitation / renovation, then replacement should be considered.
The replacement in most of the cases needs to be carried out during flow-on condition. Hence construction gets
associated with temporary flow diversion works also. If the open cut excavation is not feasible due to dense and
continuous trafficked condition of the urban area, sewer repairs / rehabilitation / renovation / replacement is carried
out by various trenchless technology methods.
Amongst the various projects under implementation in India, the Bangalore Water Supply and Sewerage Project – II, a
mega project, funded by Japan International Cooperation Agency (JICA), is under execution wherein Sewer
Rehabilitation and Replacement is a major component along with other water supply and UFW works.
Project Description
Bangalore, the “Silicon Valley” of India, is among the fastest growing cities in Asia and is one of India’s rapidly
developing modern urban centers with quality residential complexes; tree lined street corridors, parks, natural valleys
and lakes. Bangalore City is fast developing as an administrative, industrial, trade, commercial and educational centre.
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The water supply and wastewater systems within the municipal limits are under the management of Bangalore Water
Supply and Sewerage Board (BWSSB).
Among other objectives of the project following are major works to be implemented:
• Augment the water supply by about 500 mld and improvement in transmission and distribution system to reduce the
water leakages and unaccounted for water (UFW)
• Augment the sewerage system for the augmented water supply, this includes design of trunk sewer system, SPSs
and STPs, rehabilitation/replacement of existing sewers, pumping stations and treatment plants.
Bangalore Sewerage System
The sewerage system of Bangalore was first developed in the 1920’s which was confined to the heavily populated area
in the heart of the old city and it was gradually expanded to the adjacent areas. In 1950-70’s a major expansion of sewer
system was done in the city. According to the topography the city was divided into 4 major valleys Vrishabhavathi,
Koramangala, Challaghatta and Hebbal Valleys and 6 minor valleys the Kathriguppa and Tavarekere to the south, the
Arkavathi to the west, Hebbal Minor valley-I & II to the north-east and Koramangala minor valley to the east. The
valley wise sewerage system is shown in the figure given below.
The major drawback of the Bangalore sewerage system is large quantity of sewage is now flowing into storm water
drains. Because of this there are tremendous environmental issues in the entire city including the river and lake
pollution, etc. It is estimated that about 400mld of 615mld sewage generated in the city (i.e. 65%) flows into storm
water drains due to in sufficient capacity in the old trunk sewers built in the seventies. In order to address these
problems, BWSSB has taken remedial actions by way of preparing Environmental Action Plans (EAPs). Bangalore
Water Supply and Sewerage Board (BWSSB) have taken steps to rehabilitate, renovate and upgrade the trunk sewer
systems to substantially prevent the flow of raw sewage into the drains. Various Consulting Engineers have carried out
the field studies and condition assessment of existing sewerage system, hydraulic design and analysis for future
requirement using computer based models and have came up with various proposals for upgrading the overall sewerage
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system. BWSSP-II consists of three (3) parts, that is Environmental Action Plan-B (EAP-B), Environmental Action
Plan-C (EAP-C) and ISPSs. Implementation of Environmental Action Plan-A (EAP-A) is almost completed.
EAP-B works were further divided in to 7 contracts (S2A, S2B, S2C, S2D, S2E, S2F, and S2G) and the major works
are Rehabilitation/Replacement of RCC trunk sewers in various areas. Some of the packages of EAP-B works are
funded by JNNURM and are given below.
Contract
Name of work Mode of Funding
number
Hebbal Valley
S2-A JNNURM
Challagatta Valley
S2-B JNNURM
Vrishabhavathi
S2-C JICA
Valley
Koramangala Valley
S2-E JICA
Katriguppe Valley
Tavarakere Valley
S2-F JICA
Arkavathy Valley
Koramangala Sports
S2-D Complex to K&C JNNURM
Valley STP
Laying of Sewers by
Trenchless
S2-G JNNURM
Technology in all the
Valleys
The selected pipe material for sewers is RCC and of NP3 class. For further enhancement of longevity and corrosion
resistance, it is proposed to provide internal lining to the trunk sewers in all the packages.
Induced Corrosion in Sewers
Hydrogen Sulphide (H2S) induced corrosion is a serious problems in sewers in tropical climate. Often the design life
span is considerably reduced and in some areas to one thirds to half. Often very expensive rehabilitation measures by
lining or coating are implemented to enhance the structural capacity of the corroded sewers. It is very important that
since sewer systems are often designed for a life span of 30 to 50 years but in reality, the life span is considerably
reduced due to hydrogen sulphide induced corrosion.
The main mitigation measure to overcome the corrosion problems caused by H2S in sewer is to install pipes that are
resistant to hydrogen sulphide attack.
H2S that escapes as a gas from solution in a sewer may be oxidized on exposed surfaces. If the surfaces are quite dry,
free sulphur may be formed, but under moist conditions a species of bacteria named Thiobacillus, concretivorus
oxidizes it to sulphuric acid by the reaction:
H2S + 2O2 H2SO4
The acid causes corrosive damage to vulnerable materials such as concrete.
There are several pipes types of corrosion resistant pipes are available on the market and the most traditional pipe is the
Glazed Stone ware pipe. Bedsides there are many other resin based pipes such as uPVC, GRP, HDPE etc. are available
in the market.
The existing Bangalore Sewerage System uses salt glazed stoneware (vitrified clay) pipes for pipe sizes up to and
including 300mm, and RCC pipes of NP2/NP3 class for larger diameter pipes. Both types of pipe are rigid jointed, a
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collar being used to joint butt ended pipes secured by cement mortar. With the passage of time such joints have
deteriorated due to their inability to withstand stresses caused by even minor pipe movements/settlements and due to
shrinkage cracks in the mortar/concrete leading to partial or total loss of seal.
The pipe and joint materials should be:
1. Chemically stable and corrosion resistant to wastewater and external aggressive soils and ground water.
2. Chemically stable and internally corrosion resistant to hydrogen sulphide and industrial discharges and externally
corrosion resistant to aggressive soils and ground water.
3. Resistant to microbiological attack.
4. Impermeable and sufficiently abrasion resistant.
Therefore the pipes have to be internally lined so that to avoid exposure to the sulphide environment. Lining is required
for both old existing corroded pipelines as well as for new installation to increase the longevity of the pipeline. Proper
CCTV inspection has to be done before doing lining to know the exact cause and the nature of problem. There are
various types of lining available in the market with different brand names and different chemical compositions.
The various types of lining available in the market are as given below:-
(i) Polyurea Lining
(ii) PVC Lining
(iii) RotaLoc Lining
(iv) HDPE Lining
(v) METACHEM Paints
(vi) High Alumina Lining
(vii) Purethane
(viii) Ultraviolet (UV) Lining
Description of Methods
(i) Polyurea is a type elastomer that is derived from the reaction product of an isocyanate component and a synthetic
resin blend component. The isocyanate can be aromatic or aliphatic in nature. It can be monomer, polymer, or any
variant reaction of isocyanates, quasi-prepolymer or a prepolymer. The prepolymer, or quasi-prepolymer, can be made
of an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin.
The resin blend may be made up of amine-terminated polymer resins, and/or amine-terminated chain extenders. The
amine-terminated polymer resins will not have any intentional hydroxyl moieties. Any hydroxyls are the result of
incomplete conversion to the amine-terminated polymer resins. The resin blend may also contain additives, or non-
primary components. These additives may contain hydroxyls, such as pre-dispersed pigments in a polyol carrier.
Normally, the resin blend will not contain a catalyst(s).
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Polyurea protective elastomeric coatings have very unique properties.
• Completely waterproof.
• Flexible, impervious coating—bridges cracks.
• Fast cure time.
• Can support foot traffic in minutes.
• Very durable and abrasion-resistant. Wears very well.
• Resistant to many solvents, acids, and corrosive compounds.
• Many formulations available for virtually any application or need.
• Very wide range of thicknesses available in a single spraying.
• No VOC's (volatile organic compounds) released during application.
• Creates a seamless surface.
• Polyurea is much more durable than paint and typically lasts much longer between maintenance cycles. Polyurea is
the clear choice when it comes to cost/performance payback and operation. Fast cure, chemical and abrasion resistant,
concrete primary and secondary containment linings.
(ii) PVC liner consists of a continuous plastic profiled strip which is spirally wound into the existing deteriorated host
pipe. The spiral widening takes place between two manholes. Once it has been wound into place a tension wire is cut
allowing the lining materials to expand against the host pipe. A lubricating sealant within the winding acts also as a
sealant thus sealing the liner from the outside host pipe.
(iii) Rotaloc is a full-bore spirally wound PVC liner that restores the structural integrity, reliability and efficiency of
aging sewers, gravity pipelines and culverts with diameters from 800mm to 1,500mm. Rotaloc consists of a single,
continuous strip of PVC, which is progressively wound into the existing pipeline by a Rotaloc winding machine. No
excavation is required and installation can be achieved from existing access chambers. The Rotaloc winding machine
traverses the pipeline at the same time as it rotates and locks the edges of profile strip together. The machine can alter is
diameter as it moves through the pipe to ensure the liner fits tightly against the host pipe, even if its diameter changes
along its length. On site set-up requires access from both manholes during installation – one for the Rotaloc winding
machine and one for the profile. Cementitious grouting of the void between the liner profile and the host pipe can be
offered in order to meet specification requirements. Made from proven uPVC grade pipe materials, Rotaloc provides a
flow efficient smooth bore circular cross-section. The flow resistance coefficients of Rotaloc are the same as those
applicable to new PVC sewer pipe and because the liner is installed to fit tightly against the existing pipe wall there is
minimum loss of cross-sectional area. Installation is easy and fast, with minimal set-up required. There is no need to
excavate launch pits and no on-site pipe storage means smaller site foot-print, smaller support vehicles means less
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disruption to local traffic. The winding process is controlled and monitored remotely above ground so there is no need
to work inside the deteriorated pipeline; an obvious safety benefit. With no resins involved the process is cleaner and
safer and there is no waiting for curing or heat treatment. Rotaloc can be used to line large diameter pipes, drains and
culverts constructed of brick, concrete, glass reinforced plastic, or corrugated metal.
(iv) HDPE lining provide an effective isolating barrier against concrete corrosion for concrete structures, sewer pipes,
tunnels, manholes, chemical tanks, landfill, water reservoirs, wall in sewerage installations or civil foundations and
other masonry work requiring protection from aggressive media and in corrosive conditions. HDPE lining system is a
continuous, extruded and homogeneous plastic sheet membrane of flexible Polyethylene that is especially compounded
to provide maximum resistance against chemical attack. The lining is extruded with T-ribs spaced 64 mm apart on one
side of the sheet. The Tees anchor the lining into the concrete, thus making it integral to the structure. Whether it is a
concrete pipe or wall; during construction the lining is attached to the forms and secured in place. The T-ribs are always
in contact with the poured concrete which flows around them and is then vibrated to ensure a dense, void-free structure
with the HDPE lining secured to its face. The HDPE linings could be produced in different forms, profiles, properties
and colours to suit the intended use and the current production program covers linings of thickness 1.0 to 5.0 mm, other
thickness could be supplied upon demand. HDPE linings ensure concrete protection for over 100 years, all under the
quality and design requirement of ISO 9001:2000; ISO 14001:2004 and OHSAS 18001:1999.
Characteristics
• Economical
• Corrosion Resistant
• Zero Leak-Rate
• Hydraulically Smooth
• Fatigue and Surge Resistant
• Longevity
• Tappable
• Scratch Tolerant
• Chemically Resistant
• Readily Installed Small to Big Diameters
• Non-Toxic, Non-Tasting
• Lightweight, Strong and Ductile
• Flexible and Coilable
• Heat-Fused
• Mechanically Joined (As Needed)
• Weather and Impact Resistant
• Freeze Resistant and Durable
• Abrasion Resistant and Inert
• Self Restrained Pipe (Monolithic)
• Listed and Approved
• Reliable and Available
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(v) Meta-chem is an anticorrosive paints which protects the pipe from corrosion and available in 701, 701A, 701R, 702,
703, 704, 709, 711, 715, 716 in the market.
Special Features
• Single pack system, no limitation of pot life.
• No primer required, it is self priming.
• After drying forms elastic skin (Elongation 430%) which take care of expansion and contraction.
• Coated skin is fire retardant.
• Tensile strength of the skin is 18 to 21 kg. per sq. cm.
• Water and air permeability of the skin is nil.
• Skin is not brittle, so no cracking even after prolonged exposure to open atmosphere or salty soil.
• Coating is thermoplastic and no layer to layer separation even in multiple layer application.
• Easy to carry out patch repair at site at any time.
• Static charge is not developed on the surface like on any plastic material.
Specification
• Long Chain Graft Co-polymer
• Elastomeric Coating having 450% Elongation
• Fire-Retardant coating. Passes BS 3119 specification.
• Salt spray Test : Passes 1000 hrs Salt spray test
• Coating skin is 100% impermeable to air & moisture.
• Temperature Resistance : - 45 degree Celsius to 150 degree Celsius (will withstand temperature variation)
• Thermo Plastic Coating: Helps in future maintenance by forming single monolithic layer with the fresh coat.
• Single Pack, Self Priming Material
(vi) High-alumina cement is rapid-hardening cement made by fusing at 1,500 to 1,600 °C (2,730 to 2,910 °F) a mixture
of bauxite and limestone in a electric furnace or in a rotary kiln. Suitable bauxites contain 50 to 60 percent alumina, up
to 25 percent iron oxide, not more than 5 percent silica, and 10 to 30 percent water of hydration. The limestone must
contain only small amounts of silica and magnesia. The cement contains 35 to 40 percent lime, 40 to 50 percent
alumina, up to 15 percent iron oxides, and preferably not more than about 6 percent silica. The principal cementing
compound is calcium aluminate (CaO · Al2O3). High-alumina cement gains a high proportion of its ultimate strength
within 24 hours and has a high resistance to chemical attack. High alumina cement has been used to line the interior of
RCC pipes intended for sewage transportation. Defects occurring in the production line include waves, ripples, knots,
strip cracks, milky layers, crack network, non uniform thickness, breakage and roughness. It is known to line the
interior surface of RCC pipe with a cementitious mortar or cement lining for the transmission of sewerage, such cement
lining also may be coated with an asphaltic based coating. Accordingly, the major goal is to provide a substantially
crack free and void spot free cement lining and also an impervious coating on such cement lining. However, in
applications of such lined RCC pipe for sewer use, the exposure environment is quite more severe and the potential for
an acidic environment, in the low pH range, is possible. Accordingly, the concerns about corrosion increase
tremendously in such service.
(vii) Purethane is 100% solid polyurethane coating for long term protection of concrete in immersed, splash and buried
environments against corrosion, abrasion and impact. The products available in the market are Purethane®386/9000,
Purethane® 386H/12000, Purethane® 486S/6000, Purethane®AR Primer, Purethane® P-IV Primer, AmshieldDeck ™,
AmshieldDeckLT™
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PURETHANE® 386/9000
• Leading product of the series. Hard yet flexible with exceptional mechanical properties like impact and abrasion
resistance as well as corrosion resistance. Versatile product with multiple applications.
• Data sheets of Purethane® 386 H/ 12000 and Purethane® 486 S / 6000 currently available on specific request.
Amshield DeckTM
• 100% Solids Elastomeric Polyurethane formulated as a two components, long pot life, self leveling, trowel applied
coating used principally for floor and roofing applications.
• Data sheet of Amshield Deck LT ™ currently available on specific request.
PURETHANE® P-IV PrimerTM
• 100% Solids, Damp Tolerant, two component polyurethane primer with excellent adhesion to damp and dry concrete.
PURETHANE® AR PrimerTM
• A modified Polyurethane primer for steel provides excellent adhesion.
Special Features
• 100% SOLIDS
• HIGH CHEMICAL RESISTANCE
• HIGHLY IMPERMEABLE
• ADHESION
• OUTSTANDING ABRASION RESISTANCE
• EXCEPTIONAL IMPACT RESISTANCE
• CATHODIC PROTECTION
• ELONGATION AND FLEXIBILITY
• EXCELLENT WEATHER RESISTANCE
• UNLIMITED BUILD
• RAPID APPLICATION AND CURE
• HYDROPHOBIC NATURE
• RETARDS FLAME
(viii) UV lining is a new advanced No-dig sewer repair process now available from Dyno-Rod, the market leading
emergency drain repair Service Company. The system is designed to provide fast repair of sewer pipes and its speed of
installation. The liner, which is impregnated with resin, is cured quickly by using a UV light train. A Saertex®-LINER
is used, which factory impregnated with either a vinylester or polyester resin, custom is made to the specifications of the
pipe to be repaired. The impregnated lining is shipped directly to site where it is winched through the host pipe. After
installation the UV light train is inserted into the lining and the ends sealed. The impregnated line is inflated against the
host pipe using compressed air. The light train is then pulled through the lining initiating a cure. Once cured, any lateral
connections are re-opened using special robotic cutters and where required suitable ‘Top Hats‘ installed between the
host pipe and lateral. The Top Hat System is designed for lateral connections to lined pipes and consists of a factory
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stitched polyester felt top hat impregnated with an epoxy resin. The impregnated top hat is fitted on to the collapsible
arm of the robotic equipment. The robot is then maneuvered into the host lining so that the top hat is located over the
cut lateral opening. The robot is then locked in position and the flexible arm containing the top hat is inflated into the
cut lateral opening. Once in the correct position the top hat is heated to 60°C and cured for 45 minutes sealing the gap
between the host lining and the lateral pipe. After the curing process the flexible arm is retracted into the robot and
removed from the host lining. Dyno-Rod can install the top hat system from the host pipe up to 18 metres along the
lateral connection from within the host lining by using their specialized robotic equipment. This technology allows
Dyno-Rod to provide a No-dig solution for bridging the gap between the host lining and the lateral connection for most
drainage and sewerage. With these new UV Linings Dyno-Rod engineers can now provide a highly efficient solution
for the renovation of pipelines.
Project Recommendation
From the Techno-economic analysis, RCC pipe with corrosion protective material viz., High Alumina Cement lining
(<900mm diameter pipes) and PVC lining (>900 mm dia pipes) are found technically sound and economical.
For the BWSSP-II Project polyurea / high-alumina lining and PVC lining is recommended and the same has been
floated in the tender document for the execution of the work. Both types of lining are adopted for different diameter of
pipe for BWSSB Project in EAP-B Contract (Sewer Rehabilitation and Replacement work). The detailed table is given
at the end.
Installation Procedure
Inspection: Prior to commencing any work in the pipe, an inspection is needed to determine what conditions in the pipe
are encountered and what scope of work has to be done.
Cleaning: The host pipe needs to be cleaned of any debris, intrusions, deformations, mineral deposits, etc.
CCTV Drain Inspection: Because drains are largely hidden from view, the exact cause and nature of the problem may
not be immediately apparent. Sometimes, nothing less than a visual assessment of a problem will meet the need. In such
cases, television provides the full picture. CCTV surveys of drains, pipes, and sewers provide an accurate and cost
effective way to detect problems to the source and help establish the most practical remedial options. When problems
with drains or pipework are to be avoided at all costs, CCTV enables potential faults to be identified before they become
a problem. A CCTV Survey can be carried out with the minimum of fuss and disruption. The process is as follows:
STEP-1
The CCTV camera is introduced into the drain via the appropriate access point and pushed or powered through the pipe.
STEP-2
As the camera travels along the pipe, the image is relayed to a monitor screen above ground. The operator will then log
any structural defects and record the location of each along the pipe length.
STEP-3
The survey report is then provided which lists the type and location of any defect. This can be backed up with
photographs, video or CD evidence together with a site plan showing the drain's location.
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Structural Faults That CCTV Can Reveal
There are many different types of structural defects that can occur in underground pipe work. Some examples are
pictured below.
Defect: fractured pipe
Cause: Pressure above ground
Consequences: Cracks or fractures in drains leak water which destabilizes the surrounding soil.
This will result in further damage to the drain and even subsidence to buildings near by.
Defect: collapsed drain
Cause: Several possible causes
Consequences: Drain becomes unusable with high likelihood of frequent blockages,
environmental damage, and building subsidence.
Defect: tree roots
Cause: Roots seeking moisture
Consequences: Materials flowing through the drain will snag on the roots causing continual
blockages. Roots dislodge or crack the drain resulting in leakage and further damage.
Installation: One at a time, the Link-Pipe Insta-Liner™ links are coupled together and are pulled into the existing host
pipe by a winch from the far host pipe opening. Often, only pulling by hand is required.
End-Sealers: Once the Liner has been installed, End-Sealers are inserted at each end of the new Liner. This prevents the
grout from escaping when it is pumped into the annular space. The Grout is then injected into the annular space, either
through a Plug into the individual sections, or by pumping through an end nipple throughout the length of the liner.
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Acknowledgement
Authors would like to thank TCE management for their encouragement for writing this paper.
References
The following documents were referred during this paper writing:
i) Various BWSSB Project Reports.
ii) Internet Web Literatures from the following sites:
www.amchemproducts.com/
www.dyno.com/
http://en.wikipedia.org/wiki/Wiki
http://www.rotaloc.com/
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