Lining up a top solution
A culvert rehabilitation and strengthening project in Ireland proved just how effective cured-in-place pipe technology can be - even in the most challenging of circumstances.
The project was part of the Ballyogan Landfill Stage 2 Capping contract. The culvert rehabilitation project was designated as the Ballyogan Landfill Site Carrickmines Dublin 18 works.
The client for the works was Dun Laoghaire Rathdown County Council with RPS Consulting Engineers (RPS) acting as its engineering consultant. The main contractor for the project was Priority Construction, and the lining works were subcontracted to specialist contractor Insituform Environmental Techniques (IET), a subsidiary of ITL.
The Ballyogan Landfill and Recycling Park (BRP) is in the Townland of Jamestown, Carrickmines, south-west of Dun Laoghaire. The surrounding area is characterised by a mixture of agricultural, recreational, residential, commercial and industrial land use.
The total site area is 62 hectares, 43 of which were used for landfill. The BRP occupies 11 hectares. The remaining area consists of the landfill site entrance and service roads, site compound, landfill gas combustion plant, methane stripping plant and other services.
The permanent cap is in place on one part of the landfill. This area is defined as the Stage 1 Area. The remainder of the area is being capped under the Stage 2 Capping Contract, the deal under which the culvert lining sub-contract is designated. A Strategic Improvement Plan (SIP) carried out for the landfill highlighted that the twin 1,350mm diameter culverts were at a risk of structural failure due to their location and age and required rehabilitation.
The twin culverts, which extend through the body of the landfill site, convey the Ballyogan Stream through the landfill.
After careful consideration of the options available it was decided that rehabilitation would be most efficiently and cost effectively achieved by using two single shot installations, each 271m long, using cured-in-place pipe (CIPP) lining technology, a form of lining in which IET specialises.
Insituform CIPP technology was chosen because it offers a completely non-man entry trenchless rehabilitation system and provides structural integrity whilst not resulting in a significant reduction in the cross sectional area of the culverts.
Before beginning the installation of Insituform CIPP, the culverts were cleaned and CCTV surveys were undertaken to assess the extent of any existing damage to the pipe structure. The CCTV report detailed structural faults along the length of the culverts that ranged from Grade 1 to Grade 4 status. Cracks found in the culverts may have been due to overburden loading, the hydrostatic pressure exerted by the landfill leachate on the pipes and/or the corrosive potential of the landfill leachate to degrade the concrete of the culverts.
While these cracks did not pose a short-term risk to the structural integrity of the culverts, it was considered prudent to take early remedial action to ensure that the culverts did not deteriorate any further and that they remain structurally sound into the future.
Once the decision had been made as to which technique provided the most effective rehabilitation solution the next challenge was getting it installed. IET used a CIPP liner manufactured and supplied by ITL.
One of the main obstacles to a simple installation solution was the proximity of the installation site to the Arklow Carrickmines 220kV electricity substation. Power lines from the substation pass directly over the inlet of the river culverts.
This meant that there was a maximum permissible machinery reach and height restriction of 4.5m. Although a heavy duty scaffolding arrangement could be constructed at the liner launch site, no crane could be used to feed the impregnated liner to the scaffold.
The site was off the beaten track, which meant access was difficult for the installation equipment. These difficulties were overcome, first by building an access road from the main road to a new parking area adjacent to the launch site, and second, the introduction of roller beds to convey the liner from the delivery vehicle to the culvert insertion point, minimising the headroom required.
In all, the lining works were scheduled as a three-week programme starting last August with a finish date of September 2009. Once the site was prepared and the liners ready to invert, the liner installations took just three days each to complete, including installation and hot water curing.
Working in a river environment meant the flow had to be diverted continually. RPS liaised with residents, environmental organisations and the Electricity Supply Board, as well as the client at the design planning and construction stages.
For RPS, Cora Plant, senior civil engineering consultant, says: "During our preliminary assessment for the rehabilitation and strengthening of the Ballyogan Stream culverts, the methods we envisaged using came with health and safety risks that had to be managed - the prospect of an extensive construction phase within a live stream which was liable to flash flooding and the loss of available capacity within the culverts.
"The solution of the Insituform CIPP liner for the culverts removed the health and safety risk and presented the prospect of a significantly shorter programme. At execution, these benefits were realised."
Cormac Bradley, RPS construction manager, adds: "From an environmental perspective, the Ballyogan Stream, which runs through the culverts, is a fish breeding river monitored by the Eastern Fisheries Board. The methodology and environmental impact of the proposed works was subject to the Fisheries Board's approval. There was also a specific window of opportunity in which the works could be carried out."
Bradley adds: "This project ran exceptionally well with the works almost completed before we had grown accustomed to the team being on site. Within three weeks the project was complete, from site establishment to site departure."
Paul Smyth, IET director, says: "In this project, we have carried out the largest CIPP lining job in Ireland to date in very difficult conditions while completing the work both on time and on budget."