Lining up for the future
Climate change has brought more and more heavy rainfall events and flooding across the nation. The maintenance of culverts beneath vital infrastructure has never been so important.
Original pipe material also varies and includes circular, rectangular, egg-shape, oval, horseshoe and other non-standard shapes and materials from brick, concrete, stone, corrugated steel and others.
Much of the focus of water industries is aimed at projects and products related to either the potable water supply or foul/wastewater removal.
However, the arguments for the effects of climate change and the increasing likelihood of heavy rainfall events, public awareness and concern have raised the need to ensure that the facility handling surface water and storm water flows via culverts and other drainage systems is maintained as close to full operating, maximum flow handing condition as possible to safeguard against future potential flooding events.
In the past few years, we have seen major flooding incidents with increasing concern amongst environment agencies, local authorities and the general public that the removal of surface water is not the priority it should be. Some of these incidents have highlighted the need to ensure that culverts, in particular those established to manage flows beneath vital infrastructure such as roads and railways and those that divert flows to protect housing and businesses, are maintained at the highest level. Household waste, shopping carts, weeds etc. have been found to cause material build-up in many of these culverts thereby reducing their capacity significantly and in some instances damaging their structural viability, leading to overflow and subsequent local flooding.
With the complete replacement of many of these culverts being impractical because of their location in relation to infrastructure, many of the responsible authorities have instituted major culvert investigation programmes and where necessary rehabilitation programmes to bring existing culverts to full operating capacity to ensure that these key elements in countrywide flood defence and infrastructure protection efforts are at their maximum readiness.
Given the wide variety of clientele with culvert structures in their area of responsibility, including the likes of the Environment Agency, British Waterways, The Highways Agency, local authorities and Network Rail, for instance, all of which having varying degrees of deterioration and structural integrity problems, it is not surprising that there is a wide variety of potential techniques available to complete their rehabilitation. Most of the techniques can also be utilised in a variety of different circumstances. The simplest rehabilitation technique is to clean the culvert out. In many instances simply removing the blockage is sufficient to bring the culvert back to full operational readiness. In many other circumstances however the age of the culvert, the original construction materials used and minimal care over the years proves further techniques are required. This is where the experience of companies such as ITL meets the market's needs.
Standard CIPP liners comprise resin impregnated needle felt material which is generally inverted into the host culvert using water pressure or compressed air, depending on the curing process being used, from a scaffold tower or inversion drum/CHIP unit. Hot water is circulated or steam is passed through the inverted liner curing the resin and completing the installation.
The recent introduction of the iPlus Composite inversion liner system has made it possible to complete similar linings with a thinner product whilst providing the same or stronger structural lining due to the inclusion of high strength reinforcing fibres in the fabric of the liner during its manufacture. The iPlus Composite design is fibre-reinforced and is ideal for rehabilitating medium- to large-diameter gravity pipes, including culverts from 610mm to 2,100mm.
Reinforcing fibres integrated into the pipe wall form a laminated sandwich structure
with improved physical properties and providing a proprietary product.
The improved flexural strength makes iPlus Composite liner an excellent material choice for non-circular cross-sections that contain straight sides (i.e. egg shapes or flat bottom arch pipes) as well as those likely to be subject to higher than usual external loadings (i.e. consistent long-term traffic flows).
GRP lining is classed as a segmental lining system, meaning it utilises preformed/prefabricated liner sections as the basis of the lining system.
A GRP (glass-reinforced-plastic) liner is essentially a fibreglass/resin product, which is factory manufactured and moulded to the precise size and shape of the pipeline it is designed to rehabilitate.
The design is normally based on the minimum dimension permissible within the deteriorated culvert under repair. This ensures that the liner can be installed throughout the culvert length without any deformation in the host pipe that prevents access. GRP liners can also be utilised to negotiate bends in culverts by utilising short length liner pipes.
As the GRP liner segments are preformed to the minimum dimension of the host pipe, installation is normally achieved manually with specially fabricated end profiles. This linked together closely to ultimately form the completed lining length. Within the culvert, the liner segments are positioned using spacer blocks to create the lining, with an annulus between the liner outer wall and the pipe inner wall.
Normally this annulus is grout filled as the lining construction advances. This provides the necessary bond between the host pipe and the new liner and adds to the structural integrity of the completed system.
The Intergrout renovation system seals all leaks and restores the compressive ring strength of brick and masonry arches. A man-entry technique, this method of filling the cracks and voids with high strength polymer-reinforced grout has been proven to be effective in all sizes of sewer.
It is a cost-effective solution to problems caused by erosion and the breakdown of the original structure. Installation is completed by drilling small diameter holes into the liner wall and injection grout then fills voids around and within the culvert structure forming the required seal.
Where injection sealing is not required but where deterioration in the culvert wall is due to misplaced mortar or missing brickwork, re-pointing and brick replacement can be utilised. Ferrocement lining utilises a mesh support structure that is normally constructed within the host pipe/culvert at the section to be lined. A special cement mortar is applied to create the ferrocement structure. The system creates a WRc Type I liner once cured.
Advantages of this system are that it can be used to repair discreet/localised sections of a pipe such as the invert section if this is where the pipe's problem is located. It is also suitable to complete 'whole pipe' linings.
The Insituplate System was developed from ITL's extensive background in belowground construction techniques coupled with the use of GRP lining units in major pipe renovation schemes. The installation of the system starts with the excavation of the existing pipe/culvert invert to a predetermined profile for a distance of 600mm or 1,200mm.
The pre-manufactured Insituplate segments are then installed and fixed in place to the required line and level. The completed ring is then grouted into position. The process is then repeated as necessary to complete the renovation length required. This ensures that the culvert structure is supported
at all times during the installation process.
ITL also utilises a form of spiral lining system known as Danby. The Danby Pipe Renovation System has proven to be a very cost-effective method of lining. The basic material used is PVC that is delivered to the jobsite as a standard flat coil of material. Coiling the liner material inside the host culvert allows the specially designed edges to be united to form the spiral liner.
To complete an installation, the annulus between the liner and the old pipe is an important and integral part of the process in all applications. Annulus grouting not only provides important structural properties, but will also produce some level of repair to the old pipe by filling cracks and voids.
The effect of any diameter reduction on hydraulic capacity is offset in most cases by the lowering of the hydraulic flow resistance of the new PVC liner-grout-pipe composite structure.
Danby has the advantages of minimising loss of internal pipe diameter, structurally improving the old pipe, and protecting it from further degradation. The PVC liner is impervious to hydrogen sulphide and many other corrosive substances
ITL has over the past few years been constantly involved with projects for the repair and rehabilitation of vital culverts across various industry sectors and regions of the UK.
At Bilston Glen near Edinburgh, Scotland client British Coal, through its main contractor Thomas Menzies, was required to make repairs to joints in a 1,680mm high x 1,400mm wide x 564m long concrete twin box culvert.
Whilst the main structure of the culvert was sound, the deteriorated state of the joints within the culvert meant that there was a potential for failure of the culvert at some point in the future that needed to be prevented.
After careful inspection of the faults, the main contractor brought in ITL to complete the repairs using a technique involving cutting back of the defective concrete and effectively re-pointing the joints to repair them using hand-applied mortar.
In other instances whilst the joint concrete was not deteriorated, the joints were leaking. Here it was decided to drill the leaking joints and inject polyurethane foam to seal off the infiltration flows.
Another project was the rehabilitation of a culvert system in Ottery St. Mary, Devon. Here the culvert in question, known as the Ottery culvert, originally built in the late 1800s, was believed to be the problem behind extensive past flooding. This was as a direct result of the limitations of capacity of the brick culvert designed to carry a watercourse beneath the town.
As population and highway traffic increased over the years, the old watercourse was typically placed in extensions to the culvert to allow town development to continue.
The culvert took the form of a shallow brick arch following the meandering line of the original stream running the length of the town. Ottery St. Mary is a thriving small town with narrow, winding streets. Although busy throughout the year, extensive traffic build-up occurs during the tourist season. In some sections, the culvert carrying the watercourse had been built over.
In view of this, the construction of a culvert of sufficient capacity was needed to eliminate future flooding risk. This presented major problems given the constraint of the need to minimise surface disruption.
The existing culvert varied in dimension and form of construction but over the majority of its length is some 2m wide with 400mm high side walls and a maximum height to the arch mid-point of 850mm.
The sidewalls were built with a mix of stone and brickwork. The shallow arch was constructed entirely in brickwork but with several short replacement sections constructed in reinforced concrete.
Whilst the lower sections of the culvert were to be replaced using open cut techniques through a wide roadway and car park, construction of the upper reaches of the culvert, which passed under the town centre and in some cases directly under existing buildings, presented more difficult and potentially more costly problems, all with disruptive consequences to traders and town traffic.
The requirement for offline replacement, imposed by the fact that the line of the existing culvert passed directly through narrow passageways and under buildings, further exacerbated the potential cost and extent of this disruption.
Working in close association with the Environment Agency's design engineers, WS Atkins, and the partnering contractors, Van Oord/TJ Brent, ITL prepared a less disruptive solution for construction through the most seriously congested section of the culvert renewal scheme. The solution proposed was the three-segment GRP based system Insituplate. A cost and value analysis was carried out on the preliminary budget figures and the final submission was benchmarked by a competitive tender prior to placing the contract with ITL.
Ultimately the project was completed on time and within budget to the satisfaction of the client, its main contractors and the town's people of Ottery St. Mary.