This project initially consisted of the survey and potential rehabilitation of approximately 160 sewers, in the area of Mallow & Mitchelstown, County Cork. The scope of the project was extended to enable other problematic sewers within both networks to be investigated. The works were required to be carried out in 2 phases
Phase 1 – Sewer Network Rehabilitation Preliminary Works
14,693m of sewers ranging in size from 100mm to 525mm were surveyed to assess their condition. In addition, 128 manholes were surveyed and their position recorded and added to the IW database
2064m of these sewers had to be cleaned using recycler cleaning units to enable the CCTV equipment to survey the pipelines. These lines had silt and debris deposits which prevented the camera traveling through the sewer
The sewers were inspected using Win-Can software where the operator graded and coded all defects as the survey was being carried out. The CCTV footage was automatically uploaded to the Web in real time and enabled the Client remote access, to inspect any sewer, once it had been completed. Upon completion of the survey USSR ltd prepared and submitted a structural and service condition report for these assets.
Irish Waters Info-Net database holds all the information relating to each IW asset. The new information from the CCTV survey regarding the sewer condition and subsequent structural grading was uploaded to the database. This enabled a risk matrix to be constructed of the relevant pipelines where the risk of collapse (Structural condition from CCTV report) and importance of the sewer (location within the network) were scored to prioritise the sewers to be renovated
A Preliminary design proposal for the sewers surveyed was submitted to the client, where the most cost-effective rehabilitation solution was proposed for each sewer length. USSR Ltd proposed the use of GRP materials and UV-cured installation techniques by non-dig methods in the form of localised repairs and the complete relining of sewers and manholes. The additional benefits of these structural repairs will be the reduction of the overall hydraulic load due to the elimination of infiltration and the sewer and manhole rehabilitation contract will also improve the structural integrity of the existing drainage system, prolonging its service life.
Designs were calculated using the highest ground water possible and full traffic loading. This design was reviewed by IW and agreed during a design workshop where it had to be justified on a cost and effectiveness basis.
Phase 2 – Sewer Network Rehabilitation Works
A Traffic Management plan for the renovation and subsequent over-pumping was submitted for approval.
11 manholes were identified as buried and were located, exposed and raised to existing ground level to facilitate the rehabilitation works.
835 obstructions and intrusions were removed from the sewers by robotic means. These encrustations, concrete deposits, intruding connections and broken pipe shards would have prevented the installation of repairs and decreased the pipe bore.
All pipelines were cleaned immediately prior to rehabilitation to ensure that the pipeline was free of debris and grease
4190m of full-length liner were installed from manhole to manhole ranging in size from 100mm to 375mm. Sewers with widespread or frequent defects were relined in order to return the sewer to proper operating order with minimal change in original hydraulic capacity. The INPIPE CIPP lining system proposed by USSR Ltd used a non-shrink liner that fits tightly to the host pipe that was air inverted and cured with UV light. Samples were taken of the lining materials, independently tested and were shown to have exceeded the specification requirements.
Once the pipelines had been relined, a robotic cutter reopened the service connections to allow flow back into the newly renovated sewer. A total of 333 laterals connections were reconnected in this manner. Top Hats were then applied to form a seal between the lateral and renovated sewer
In addition, 244 localised repairs were installed at isolated defects in the sewer-lines.
21 structurally compromised manholes were also relined using high density silicate reinforced mortar.
A total of 10,233m of sewer were rehabilitated during the project. A CCTV survey showing the new condition and updated Infonet database were submitted upon completion.