Environmental Techniques

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Overview: The rehabilitation of a 250m stone culvert using the spirally wound Panel Lok system to ensure integrity of the culvert during construction of a new tunnel underneath.

 Location: Limerick, Ireland

Operations:  Culvert Rehabilitation
Client: Limerick Corporation



The Limerick Main Drainage Scheme is a major environmental and infrastructure project which will provide for future developments of the area.  As well as the construction of new tunnels and treatment works it will upgrade the existing sewer network. The scheme involves the construction of a 2.82m diameter tunnel in variable ground conditions ranging from limestone to very soft water bearing silts and sands. The alignment of the Dock Road Tunnel follows the route of the original culvert along the Dock Road and there was concern about the potential consequences of a collapse on the road. 

 Dock Road is part of Ireland's major road network and carries three major gas mains

 Any collapse would cause major disruption to traffic and utilities

 No easy diversions or alternative routes 




Investigations showed the existing culvert, with a size of 1350 x 800mm, to be approximately 4.5m above the crown of the new tunnel and well within its zone of influence. Environmental Techniques carried out an internal condition assessment of the tunnel using the WRc Sewer Rehabilitation Manual (SRM) which showed the culvert to be Class 4 to 5. A number of rehabilitation options where considered including GRP, CIPP, uPVC Panel Lok and digging. After careful consideration, the trenchless Panel Lok system was chosen due to ease of installation and cost effectiveness.

After initial assessment of the culvert was undertaken, Environmental Techniques commenced the cleaning operations to remove silt and rubble from the invert of the culvert. The cleaning operation consisted of jetting and man entry to remove the larger debris. The Panel Lok system was installed from existing manholes, avoiding the need for the construction of access shafts on the busy Dock Road. The installation crew, equipped with gas monitors and safety equipment, then entered into the manhole to begin connecting the Panel Lok system in place. The flexibility of the Panel Lok system helped overcome any irregularities inherent in stone culverts. On completion of the Panel Lok system, the annulus between the uPVC and the stone culvert was filled with grout, helping to stabilise the surrounding ground.




 No disposal / haulage was necessary as would be required with a digging option

 No reinstatement of roads

 No access shafts required to be excavated as work could be completed from existing manholes

 A solution involving grouting was preferred as the grout would fill voids in the stone walls and surrounding limestone

 In the event of a flash flood, it is possible to halt works and return once flows have subsided without requiring removal of a partly installed liner.

 Despite a minor reduction in cross sectional area, the hydraulic performance of the culvert was improved due to the reduced surface roughness.

The client was seeking a holistic solution that not only strengthened the existing culvert but also filled the surrounding voids to eliminate the danger of collapse during tunneling below the culvert.

The minimal disruption of traffic offered by the trenchless Panel Lok system had great merit. The Limerick Main Drainage scheme has an excellent public education programme and the use of a trenchless solution to rehabilitate the existing culvert was particularly important to the client as it avoided the need for excavations, diversions and road reinstatement.

On successful completion of the first phase the contract was extended by 110 metres. The project was considered value for money and the innovation of the scheme was recognised at the 2003 UKSTT Annual Awards where the project won the Renovation Small Project category. 




Overview: Scheme undertaken in Dublin City Centre including CCTV and Sonar Surveying of pipes, manhole surveys, pumping station surveys and jetting of sewers.

 Location: Various locations around Dublin City Centre

Operations:  CCTV Survey, Sonar Surveys, Manhole Survey, CSO Survey, Pumping Station Survey
Clients: Atkins Ltd, Irish Water, Dublin City Council


The scope of the contract was to carry out a comprehensive survey to assess the structural condition of the ageing and complex drainage system at various locations within the south-side of the Dublin City Centre catchment and also to assist the build and verification of the hydraulic model.

Some of the constraints faced during this project

 Large diameter, irregular shaped pipes

 Semi-surcharged and surcharge pipelines

 Heavily silted sewers which had never been cleaned or surveyed before

 Working in busy city centre environment

 Requirement to avoid disruption to vehicular traffic and LUAS flows



Assessment and recording of condition of approximately 26km of foul/combined/storm sewers varying in size from 100mm to 2700mm and varying in shape (circular, egg, arch and rectangular)



Initial inspections found that major sewers adjacent to the River Liffey were in a constant surcharged / semi-surcharged state. In order to obtain a survey of adequate use to the client, Sonar surveys were carried out on these sewers using a sonar profiling system mounted on a float. In conjunction with CCTV footage, the sonar data provided much needed information on the condition of the pipe and amount of debris below the water level.


Initially, a total of 1km of sonar surveys were completed in this location ranging from 900mm diameter to1350mm. The use of sonar and CCTV on a float system allowed sewers to be surveyed for which no information had been previously collected. Due to heavy infiltration from the River Liffey, overpumping the line was virtually impossible and setting up traffic management to get the overpumping equipment, in addition to the jetting equipment, would have caused major traffic disruptions in an extremely busy location at the centre of Dublin City Centre.


A further 4km of sonar surveys were completed along Dublin’s South Quays and Ringsend area as data provided by the initial survey contractor was insufficient for assisting in the build of the hydraulic model due to the pipes being in a surcharged/semi surcharged state. Environmental Techniques were tasked by Dublin City Council and Atkins to survey these sewers with sonar following the success of the initial sonar surveys. To improve productivity, guide ropes for the sonar survey were installed at each location by a man entry team working ahead of the sonar survey squad.


The sonar survey proved invaluable for collecting information in the surcharge/semi-surcharged sewers and its utilisation in this situation led to the project being awarded “Innovative Scheme” at the 2015 UKSTT Annual Dinner and Awards Ceremony.



Many of the sewers identified for survey were brick, egg shaped culverts, with narrow inverts. Due to the size of the sewers, the narrow inverts and the irregularity of the bricks, it was not possible to undertake the survey of these sewers with a CCTV camera. Instead, man entry surveys were carried out for 1.8km of sewers ranging in diameters 1600x700mm to 2600x800mm (egg shaped). Each survey team consisted of 7 personnel all of whom were confined space trained. Video footage of the tunnels were recorded by the operative who noted defects and inspected them using the camera system.



An internal condition and dimensional survey along with a GPS/Total Station survey was undertaken for 179No. critical manholes. The position, diameter, material and invert level of every pipe entering and leaving each manhole was recorded along with the manhole construction details, condition and internal dimensions. Detailed plan and cross sections were completed for the critical manhole and CSOs.



Surveys were completed for 8No. pumping stations throughout the catchment. The surveys involved recording dimensions and levels of the pipework and assets within the pumping station chamber and a topographical survey of the pumping station site.



Through abandonment of initial CCTV Surveys, approximately 4.5km of sewers were identified for jetting to facilitate completion of the CCTV inspections. Sewer diameters varied in diameter from 150mm to 1200mm diameter. All jetting/desilting carried out on the instructions of the Client’s representative and CCTV inspections were undertaken immediately upon completion of the cleaning operations.


Environmental Techniques undertook a large majority of the works at night to minimise disruption to the vehicular traffic and the LUAS line. Through the use of sonar profiling systems and man entry tunnel surveys, the majority of the lines presented in the scope of this project were able to be surveyed providing network engineers with critical information for their models. These models were further enhanced with the detailed surveys undertaken on pumping stations and combined sewer overflow chambers, allowing critical network scenarios to be modelled.

Overview: Rehabilitation of twin 1350mm diameter culverts using CIPP liner to improve structural capacity and prevent infiltration from landfill groundwater.

Location: Ballyogan Landfill and Recycling Park, Jamestown, Dublin

Key Operations:  Rehabilitation, CIPP


The Ballyogan Landfill and Recycling Park (BRP) is located in the townland of Jamestown in Carrickmines. The surrounding area is used mainly for agricultural, residential and commercial purposes. The Ballyogan Stream runs underneath the landfill site via twin 1350mm diameter culverts, each 271m in length. A Strategic Improvement Plan highlighted the fact that the two culverts were at risk of structural failure, due to age and location, and were in need of rehabilitation.

In 2009, Environmental Techniques undertook an assessment of the culverts using CCTV surveying. Overburden loading from the landfill site and chemical attack from landfill leachate were identified as possible causes of the degradation of the pipe. 

Following analysis of various rehabilitation methods and consideration of the site limitations, Cured-In-Place-Pipe (CIPP) Rehabilitation was identified as the most suitable means of rehabilitating the twin culverts.


The CIPP liner (17mm design thickness) minimised the loss in cross sectional area and, due to the smooth surface, gave increased flow capacity

The load bearing capacity of the culverts was improved due to the structural qualities of the CIPP liner

Leakage from the landfill into the culvert was eliminated as the CIPP liner has no joints which provide an access route for infilitration

The CIPP liner has a high chemical resistance

No many entry was required which greatly improved the safety aspects of the project as the impact of flash floods on the stream was a major concern of the client

As a no-dig solution, excavation was completely avoided which would have proved difficult and dangerous in the landfill environment

The project was finished within 3 weeks from when the crews were initially on site. CIPP proved to be more cost efficient, had less health and safety risks and had a faster installation time compared with other rehabilitation or replacement options. 


The project won the Renovation - Large Project Award at the 2010 UKSTT Annual Awards for excellence on pipeline, culvert or underground structure rehabilitation projects valued in excess of £250,000. 

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