| dc.description.abstract | Three different water main lines in Trondheim municipality have been subject to several breaks and leaks. These water main lines have a total length of approx. 1.3 km and are located under the roads of Bratsbergvegen, Nordslettvegen, Saturnvegen and Neptunvegen. Due challenges redirecting traffic in the area, Trondheim municipality had to postpone maintenances for some time. Now the municipality wants to rehabilitate the pipelines with the use of trenchless technology.
Trenchless rehabilitation is construction work below the ground surface with the purpose to rehabilitate existing pipelines with limited use of trenches. The rehabilitation techniques compared in this project are pipe bursting, sliplining and close-fit lining. Relative merits of trenchless techniques have been compared to each other and to open cut trenches. The comparison analysis has focused on sustainability in three dimensions: social disturbance, environmental impact and economical sustainability. Trondheim municipality requires that rehabilitated pipes have the same structural integrity and life expectancy as newly laid pipes with use of conventional trenches. As such, several rehabilitation techniques that are not structural independent of host pipes are not taken into consideration.
The comparison includes an EPANET-simulation of the pipelines capacity under normal conditions and with increased demand of water for the use to extinguish as much as two fires at the same time. This has been done for current distributing system and for reductions in cross section of pipelines in the case of sliplining and close-fit lining. The simulation model in EPANET has not been calibrated and margin of error should be taken into consideration.
To compare cost and CO2-emissions a limited bill of quantities was made. The most relevant items for calculating the cost and emissions were decided. The items were mainly focused around quantities of soil and asphalt excavated and transported. The price of each item was set by market price of comparable projects in Trondheim. Social inconvenience was decided by amount of work.
This project has shown that trenchless rehabilitation in these cases has been favorable compared to conventional trenches. Trenchless rehabilitation has shown itself to have lower emissions, less invasive, lower workload and more economical. Cost and emissions are greatly reduced if it is possible to use pipe that is delivered coiled. This is because the coiled pipe greatly reduces the required size of the insertion pit.The greatest factor in cost reduction of using trenchless rehabilitation is dependent on the amount of lateral connections. Residential areas generally have numerous lateral connection that need to be connected to the main line after rehabilitation and every saddle point needs to be dug up. However, it should be noted that trenchless technology is more economical and environmentally friendly even with many lateral connections.
Close-fit lining has generally been the cheapest and least invasive to the environment in this project. It has however not been chosen as the best technique in any of the pipe routes. The reason for this is that there has been little to differentiate close-fit lining from the other methods, and close-fit lining has less structural strength than the other methods.
Trenchless rehabilitation cannot solve all problems, and there are times where it is not applicable. It should however always be considered in maintenance projects, and there should be good reasons for not choosing trenchless rehabilitation. | |
