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“CASE STUDY OF THE DESIGN AND
INSTALLATION OF STRUCTURAL
LININGS FOR OVIFORM SEWERS”
ALAN SUTTON B.Sc (Eng). CPEng. MIEAust.
Engineering & Overseas Development Manager
Kembla Watertech P/L
• Sydney Water Corporation (SWC), in common with other major authorities, has a number of critical sewer mains of oviform shape. While this ‘egg’ shape has the advantage of providing a self cleaning velocity at low flows, the same shape makes it very difficult to design and install a lining that will restore structural strength to the sewer without loss of flow capacity.
• Kembla Watertech was approached by SWC regarding the rehabilitation of two of their oviform sewers using a cured in place pipe (CIPP) type lining.
• This presentation will first highlight the discussions between client and contractor to design structural linings to satisfy external load conditions (e.g. 13m depth) and then will detail the installation work which was undertaken at night during restricted hours and involved large scale sewer bypass and traffic control set ups.
ABSTRACT
SHORT BACKGROUND TO KEMBLA
• Kembla Watertech P/L has been active in the pipeline
rehabilitation market since 1993
• Kembla has been actively involved with SWC since 1993
• Currently some 170 personnel and 50 installation units
• Kembla currently has Term Contracts for sewer/water main
rehabilitation with SWC, Hunter Water, South East Water, City West
Water, Brisbane Water & Citiwater Townsville.
ENVIROLINER PIPE LINING SYSTEM
• Enviroliner is a process for the renovation of pipelines by the installation of a resin impregnated flexible tube which is inverted into the existing conduit by use of hydrostatic pressure.
• The tube is cured to a hardened state while held in intimate contact with the conduit. This type of system is classified as a Cured In Place Pipe (CIPP) and is a trenchless method for restoring full structural integrity to deteriorating pipelines. A number of companies in Australia offer CIPP linings.
• The system is suitable for all diameters from 100mm to 2000mm but generally is more cost effective in the larger diameter range.
• A CIPP liner is tailor made to suit the circumference of the pipe and because it is inserted in a softened state it will take the shape of the host pipe. This makes it ideal for non circular shapes such as OVIFORM.
WHY AN OVIFORM SEWER ?• A velocity of 1 m/sec is capable
of moving solids and debris in a
pipe flow condition.
• Early studies also showed that
the lower part of a "V" channel
shape could carry sanitary waste
flow efficiently while the upper
portion had sufficient capacity to
transport storm water.
• This then led to the evolution
of the ‘egg’ or oviform shaped
pipe.
• When new sewers were
designed for London, Paris etc in
the last half of the 1800s, oviform
shaped sewers were determined
to be the best cross-section for
the larger "combined" sewers.
OVIFORM SHAPE• Over time, the “self cleaning” characteristics of the oviform shape proved to be as
effective as the engineers had projected and this shape was used extensively in early sewer construction not only in Europe but in Australia as well.
• Given that many of the first major sewers constructed in Australia used oviform shaped pipes then it is no real surprise to find that they now represent a critical component of the sewer network.
• Cities have “grown up” above these early sewers and they are most often found in densely populated areas.
• The two sewers chosen for this presentation highlight the difficulties now facing authorities with ageing oviform sewers.
• The concept of oviform shaped pipes had many advantages over circular profiles: higher flow rates during low flow periods - improved self cleaning effect -reduced trench width - higher load carrying capacity - a higher vertical profile which makes man access easier.
• The downside unfortunately was that with the advent of large diameter spun concrete pipes they became too expensive to produce or lay and were phased out as a new sewer pipe option many years ago.
PROJECT BACKGROUND• Kembla is one of two specialised contractors working on the Sewer
Rehabilitation Program 2006/09 for SWC .
• Worth stating again that SWC, in common with many other authorities, has a
number of critical sewer mains of oviform shape. While this shape has the
advantage of providing a self cleaning velocity at low flows, the same shape
makes it very difficult to design and install a lining that will restore structural
strength to the sewer without loss of flow capacity.
• Oviform GRP segments have been trialled but
have not proven cost effective because of:
- the loss of cross section
- the cost of filling the gap with grout
- the cost of the purpose-built moulds
Site 1: O’CONNOR ST HABERFIELD
A
760mm x 600mm concrete sewer in
O'Connor St, Haberfield.
This sewer is approximately 95 m in
length and includes a 90 degree bend.
760mm x 600mm approximates to a
650mmm circular liner
It was rightly identified by SWC as being in
need of urgent rehabilitation, particularly in the
vicinity of the bend where CCTV survey had
revealed holes in the side of the pipe.
The sewer is located in a roadway and
SWC asked Kembla to “investigate this matter with a view to rehabilitating this asset by installing a continuous lining.”
Site 2: LYONS RD DRUMMOYNE
At the same time as investigation was
being done on Haberfield we were
also asked to look at the lining option
for a 533mm x 406mm concrete
oviform sewer in Drummoyne.
(Approximates to a 450mm dia. lining).
A CCTV survey had revealed serious
deterioration of the inside concrete
surface of the sewer.
B
A
C
D
As shown above, this sewer was laid UNDER Lyons Rd near to its
intersection with Victoria Rd, two very busy thoroughfares.
The following factors made this job extremely difficult:
--- the sewer was 13m deep at access chamber B, which itself was
located in the middle of Lyons Rd
--- total length to be lined was 350m from A to D
--- a 225mm diameter rising main discharged at access chamber D and
the only feasible route to bypass the flow from D to A was across Lyons Rd.
--- local streets were narrow and densely populated
PHO
TO
PHOTO
CROSS SECTION OF DRUMMOYNE SEWER
Lyons Rd
13 m
deepAccess
chambers
250m length
The lining from C to A was eventually
installed in one single 250m long
installation because of constraints
with access to chamber B in the
middle of Lyons Rd. The thickness
and length of this lining made it one of
the most difficult CIPP linings ever
installed in Australia.
AB C
DESIGN OF A STRUCTURAL LINING
SWC has issued a technical specification “limited to non man-entry linings to be installed in intact oviform conduits that do not rely on any bond with the existing sewer for their structural capacity.”
It assumes that the existing sewer is in
good condition and capable of carrying
the externally imposed earth and traffic
loading. The liner is designed for
hydrostatic loading caused by a water
table located above the sewer.Oh
DESIGN OF A STRUCTURAL LINING• There were numerous meetings between Kembla and SWC design staff to
determine the appropriate design criteria to be applied. The lining was required
to be designed to satisfy the SWC performance criteria for buckling, strength,
deflection and minimum liner thickness.
• Each lining was checked for buckling with the oviform liner considered as a
circular pipe with an equivalent circular diameter of Deq = 1.75 * Ow
• Strength and deflection design was then undertaken based on the procedure
set out in the Water Research Centre, Sewer Rehabilitation Manual 2001 Volume II Chapter 5 for non circular linings.
• Calculations were carried out to ensure long term bending stresses and
strains were less than the maximum permissible values for the lining. The liner
critical length (Lcrit) is defined as the greater of Ow or 2/3*Oh and the maximum
allowable deflection of the liner (Δall) shall not exceed 3% of Lcrit. The critical
length shape factor (R) is specified as 0.5.
DESIGN RESULTS
1) Haberfield:
This sewer, although larger in dimension than the Drummoyne sewer, is only at a shallow depth and if the sewer pipe could be considered as “intact” then the design thickness required was 16 mm. This thickness was within normal limits and so the more critical aspect of this project became how to provide an ‘intact’ pipe at the deteriorated 90 degree bend.
2) Drummoyne:
The 13m depth of the Drummoyne sewer was a problem and a design thickness of over 22mm resulted from the use of the normal design criteria. This is not a practical option in a lining that correlates to a 450mm diameter. After consultation with SWC and the manufacturer of the linings as well as overseas CIPP contractors, an 18mm thickness was adopted as the maximum thickness that could be manufactured and confidently installed at this diameter.
HOW WE ACHIEVED THIS AND NOT THIS
LINING INSTALLATION
LINING INSTALLATION• Because of their non-standard size, the linings were specially manufactured at an
ISO 9001 accredited facility in the UK which supplies CIPP linings worldwide.
• Mixing and impregnation of the resin was carried out at Kembla’s CIPP factory in
Newcastle.
• Cleaning of oviform pipes is a unique process requiring special cleaning
techniques. In keeping with our
preferred policy, Kembla used its own
experienced cleaning crew and
equipment for this work rather than
sub contractor.
• To ensure no structural damage was
done during pressure cleaning and
no debris was missed that could effect
the lining installation process, we
employed a live CCTV coverage of the
cleaning process.
LINING INSTALLATION
• The impregnated linings were stacked into a refrigerated truck for transport
to site. If kept cold, the impregnated linings have a considerable shelf life
which provides a contingency against unforeseen events.
• Either a head of water or air pressure is used
to create internal pressure to the lining
which turns (or inverts) the liner inside out and
presses the resin felt composite tight against
the pipe wall.
• Because of the oviform shape, water was used
for the inversion process in this case.
• The weight of the liner required theuse of a crane to lift it from inside
the trailer into position.
• The internal pressure is maintained at all times so that the lining is held tight against the pipe wall.
• Once the lining reaches the far end hot water or steam is circulated inside the lining while the internal pressure is maintained until the lining is fully cured in place.
LINING INSTALLATION
Given the thickness of 18mm and theoviform shape, the 250m single lengthinstallation at Drummoyne was one of themost difficult ever undertaken in Australia.This lining had a total weight of 8.7 tonnesand was successfully installed over onenight ------- highlighting the speed andefficiency of this type of lining system.
PROJECT EXECUTION: SEWER BYPASS• Sewer bypass at Haberfield was reasonably
straightforward and Kembla used
its own 100mm portable pumps and hoses.
• The Drummoyne project however presented
a very difficult bypass situation where the dry
weather flow capacity had to be 165 L/sec.
• As previously mentioned the only feasible route to bypass the flow was up one narrow street, across Lyons Rd and then down to the discharge chamber.
Consideration was given to directional
drilling under Lyons Rd however this
was cost prohibitive.
Instead, a 400mm wide x 500mm deep
trench was dug by Kembla’s own civil
crews who laid 2 x 200mm lay flat hose
lengths within the trench.
PROJECT EXECUTION: SEWER BYPASS
• Coates Hire was employed as subcontractor for this activity.
• The bypass operation included maintaining balance of pump flows during
high and low conditions, fuelling of pumps, maintenance of pumps and in
the event of breakdown the engagement of standby pumps and repair of
the duty pump.
• The system employed was 2 x 200mm high pressure lay flat hoses supplied
by 2 x 200mm portable silenced diesel pumps. The lay flat hose
arrangement allowed for quick dismantling once installations were
completed.
• All entry to access chambers for plug installations was carried out by
Kembla’s site personnel who are all trained in confined space entry.
• While a logistical nightmare, the flow management strategy proved
effective and efficient in bypassing the existing sewer flow for the duration
of all site activities without a single environmental incident.
PROJECT EXECUTION: SEWER BYPASS
: sewer
600m
of twin
200m
hose
The following steps were implemented to ensure the
safe isolation of the Oviform sewer pipes.
Flow Management Plan developed and approved.
Weather checked prior to commencement of bypass.
Work to be done at night during low flow periods.
Special plug to be used on Oviform pipes.
Continuous monitoring.
Emergency spill trailer on site to mitigate spills.
PROJECT EXECUTION: SEWER BYPASS
PROJECT EXECUTION: CUSTOMER RELATIONS• Given the high profile location and densely populated streets, Customer
Relations was always going to be a major focus for both Kembla and SWC personnel.
• A preliminary meeting was held with Sydney Water Communications team to discuss details of the work, roles and responsibilities.
• After defining the perimeters for the directly affected residents and commercial customers, site specific letters were prepared detailing dates and work times for directly affected residents and commercial customers.
Directly Affected Residents
Directly Affected Commercial Customers
PROJECT EXECUTION: CUSTOMER RELATIONS
• Kembla’s Customer Relations Officer was on site at Drummoyne throughout the night work activity.
• Residents were advised of this prior to work commencing to give them a sense of assurance that there was someone on hand who was aware of their situation and who could provide them assistance should they need it.
• When the work was completed at both Drummoyne and Haberfield the Customer Relations officer visited all residents (who were home) and Commercial customers, to advise that work had been completed and to thank them personally for their patience during this time. Many advised that there had been no disruption to their life and routines at all, which would certainly had not been the case if Trenchless Technology had not been adopted.
Detailed traffic control plans were drawn up for Haberfield and Drummoyne following
extensive consultation with both Local Government and the RTA.
PROJECT EXECUTION: TRAFFIC CONTROL
The Haberfield Oviform
required O’Connor Street to
be closed for 3-4 weeks
including the time needed
to concrete encase the
bend in the oviform.
PROJECT EXECUTION: CONCRETE ENCASEMENT
• When the up to date CCTV survey was carried out on the Haberfield sewer the
condition of the bend was found to have deteriorated further than previously
observed and confirmed Sydney Water’s wisdom is nominating this section for
rehabilitation.
• Because of the design requirement
for the sewer to be in an “intact”
condition, SWC decided to concrete
encase the bend to provide long term
stability to the sewer.
• The CIPP lining was to be installed
first and this was carried out
successfully through the 90 degree
bend in its deteriorated condition.
PROJECT EXECUTION: CONCRETE ENCASEMENT
• Once the lining had hardened, the existing sewer was able to be exposed for
the encasement work without the need to bypass the flow.
• Even though a SWC approved sub contractor was used for this work they were
still required to be site inducted by Kembla before work could commence. The
civil subcontractor was required to submit an Authority to Work Permit on the
afternoon prior to commencing work the next day and this enabled us to track
the subcontractor’s activities and provided us with a check list of who will be
onsite, their skills mix and to confirm each person had been inducted.
This paper has attempted to highlight some of the design and installation difficulties
facing any authority with oviform or egg shaped sewer mains. The ‘before and after’
videos below, are proof of the ability of an experienced No Dig specialist contractor
to work closely with the owner of the asset to provide a long term rehabilitation
option for what are now ageing oviform sewer conduits.
