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  • 1.CASE STUDY OF THE DESIGN ANDINSTALLATION OF STRUCTURALLININGS FOR OVIFORM SEWERSALAN SUTTON B.Sc (Eng). CPEng. MIEAust.Engineering & Overseas Development Manager Kembla Watertech P/L

2. ABSTRACT 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. 3. 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. 4. 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. 5. 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. 6. 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. 7. 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 8. Site 1: OCONNOR ST HABERFIELD760mm x 600mm concrete sewer inO'Connor St, Haberfield.This sewer is approximately 95 m inlength and includes a 90 degree bend.760mm x 600mm approximates to a650mmm 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 A 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. 9. Site 2: LYONS RD DRUMMOYNEAt the same time as investigation wasbeing done on Haberfield we werealso asked to look at the lining optionfor a 533mm x 406mm concreteoviform sewer in Drummoyne.(Approximates to a 450mm dia. lining). A CCTV survey had revealed seriousdeterioration of the inside concretesurface of the sewer. 10. A BC PHOTO PHOTOAs 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 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 11. CROSS SECTION OF DRUMMOYNE SEWERThe 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 ofLyons Rd the most difficult CIPP linings ever installed in Australia.Access13 mchambersdeepBC A 250m length 12. DESIGN OF A STRUCTURAL LININGSWC 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 13. 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 (all) shall not exceed 3% of Lcrit. The critical length shape factor (R) is specified as 0.5. 14. DESIGN RESULTS 1) Haberfield: This sewer, although larger in dimension than the Drummoyne sewer, is onlyat a shallow depth and if the sewer pipe could be considered as intact thenthe design thickness required was 16 mm. This thickness was within normallimits and so the more critical aspect of this project became how to provide anintact pipe at the deteriorated 90 degree bend. 2) Drummoyne: The 13m depth of the Drummoyne sewer was a problem and a designthickness 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 asoverseas CIPP contractors, an 18mm thickness was adopted as the maximumthickness that could be manufactured and confidently installed at thisdiameter. 15. LINING INSTALLATION HOW WE ACHIEVED THISAND NOT THIS 16. 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 Kemblas 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. 17. 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 p