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Dublin City Centre Sewerage Scheme

Dublin City Centre Sewerage Scheme Dublin City Centre Sewerage Scheme

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

 

CCTV SURVEYS

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)

 

SONAR SURVEYS

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.

 

MAN ENTRY TUNNEL SURVEYS

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.

 

MANHOLE AND CSO SURVEYS

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.

 

PUMPING STATION SURVEYS

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.

 

SEWER CLEANING

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.

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