CULVERT REHABILITATION OPTIONS
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, etc., 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.

Of course 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.

The spectrum of rehabilitation techniques offered by ITL includes:
• Standard CIPP lining using hot water and steam cure options
• High strength CIPP installation using the iPlus™ Composite liner
• Glass reinforced plastic (GRP) pre-manufactured, made to measure lining
• Intergrout, an injection sealing system
• Man entry options such as re-pointing brickwork or site specific repairs
• Ferro-Cement lining (through ITL’s subsidiary Sewer Services)
• Insituplate lining

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 egg-shaped Bristol Water culvert lined with GRP segments and fully grouted.

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 (24-inch to 840inch). 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, etc.).

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 which 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.


Erecting metal plate liners on the Dark Lane project.

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 1200mm. The pre-manufactured Insituplate segments (normally requires three to form the complete culvert shape required) 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 which 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

RECENT PROJECTS
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. The following is a small selection of the projects completed to illustrate the variety of situations in which the company’s solutions can and have been utilised. At Bilston Glen near Edinburgh, Scotland client British Coal, through its main contractor Thomas Menzies, was required 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 which 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. The whole contract was completed between February 2009 and March 2009.

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 water course 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 (calculated to be a culvert with a minimum of 1.35m2 cross-sectional area) 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.

On a further culvert rehabilitation contract, Bristol Water Company through its main contractor, Costain, was required to renovate an existing raw water culvert taking feed from reservoirs at Chew Magna and others in the Mendips to its Barrow Treatment Works. The water is conveyed mainly in masonry culvert with sections of aqueduct which cross valleys enroute. The total length of the culvert is approximately 20km. Since the late 1980s, Sewer Services Ltd. and latterly Insituform Sewer Services have renovated various sections of the culvert.

The latest culvert section to be renovated was a 680m length at Litton. This culvert was nominally a 1,380mm x 1,095mm masonry egg shape which was rehabilitated with a 1,264mm x 960mm GRP egg-shaped liner. The resultant annulus was grouted with a PFA/Cement grout. In all, three consecutive sections of the culvert were lined over lengths of 172m, 198m and 310m respectively, totalling some 680m. Some 160t of grout was required to fill the annulus created across the project length. The purpose of the project was to renovate the old structure which suffered from the partial collapses and exfiltration of water. One of the most recent culvert renovation projects undertaken by ITL was the use of iPlus™ Composite liners to rehabilitate some 10 culverts running beneath the main A30 Trunk road off the M5 motorway into Devon and Cornwall south of Exeter.

Because of estimated future drainage flows and the load bearing capacity requirements from the increasing traffic flows on A30 Trunk road, this renovation was required to ensure the long-term operational viability of these culverts. The project was carried out with the support of the UK Highway Authority’s main contractor and consulting engineering partner, EnterpriseMouchel. The culverts were situated at different depths, in different locations and comprised of pipelines of differing diameters (varying between 1m, 1.2m and 1.6m) and pipe materials.  Each culvert was individually assessed in order to specifically design the appropriate rehabilitation liner for each individual culvert. The UK Highway Authority decided to utilise the standard Insituform® CIPP process and liner materials on six of the 10 liners and the new iPlus™ Composite liner on the remaining four sites.

The iPlus™ Composite liner was selected for the four sites largely because of the individual circumstances of each culvert, which included the culverts either running at depth below the road surface resulting in greater ground loading or the culverts being subject to high traffic and other potential external loadings which could possibly affect the long-term performance of standard liners. Another culvert rehabilitation projects undertaken by ITL was the Dark Lane project. This involved the lining of a culvert beneath the A38 Trunk road near Chudliegh, Devon known as Dark Lane Underpass. The works involved the lining of a 6,782mm high by 6,122mm wide by 48m long corrugated steel constructed underpass with an Assett Multi-Plate corrugated steel liner.

The individual liner plates were bolted together into sections prior to final assembly of the culvert liner. Each section was pre-assembled in the site compound before being craned into place in the culvert entrance. A 50t capacity pipe bursting rod puller winch then pulled the new corrugated steel liner through the existing culvert from the reception end of the culvert. To achieve the pull-in, a frame distributed the load required to move the multi plate liner across the wing walls. Successive liner rings were then assembled and added to the structure as it was drawn through the culvert. Upon completion of the installation, the annulus was filled with foam concrete.

Other projects include the use of ferrocement construction and culvert cleaning on a project in Glastonbury, Somerset; re-pointing and cementitious reinforcement of a culvert in Shepton Mallet, Somerset; intergrouting of a culvert beneath the A75/A77 between Maesteg and Spaxton in Scotland; GRP installations beneath the A20 Trunk Road close to Stanstead airport and on a project to rehabilitate a culvert in Stratford upon Avon and a multitude of culvert rehabilitation projects for Network Rail using a variety of the techniques already outlined.

For further details contact:
Insituform Technologies Ltd.
Unit 6, Roundwood Industrial Estate
Ossett, West Yorkshire WF5 9SQ, UK.
Tel: +44 (0)1924 277076. Fax: +44 (0)1924 265107.
Email: JBeech@insituform.com
Website: www.insituform.co.uk