World's largest diameter close-fit PE lining project
Subterra's patented Subline close-fit lining system was recently used to line two 1.4km lengths of twin DN 1200 pipelines with PE near Amsterdam.
The twin DN 1200 PSC pipelines were originally laid 30 to 40 years ago. While they remain in an excellent structural condition, progressive movement in areas with very poor soil has, in the past, led to joint displacement (longitudinal and angular) and consequent leakage.
In the past, the affected joints had been repaired by means of internal joint seals. For part of its length, these pipelines run parallel with, and in close proximity to, the main railway line running from Amsterdam to the Southern Netherlands and Germany, and to the E9 motorway.
The planned upgrading of the railway line to TGV status, and the associated widening of the motorway, stimulated the search for a more comprehensive and permanent solution to safeguard future water supplies.
The principal concern was that future ground movement, exacerbated by the increase in ground vibration associated with the augmented rail and road links, could lead to further joint displacement and leakage, eventually undermining rail/road foundations.
Working closely with IWACO (consulting engineers) and KIWA (the Netherlands institute for the examination of water supply pipes and fittings), and based on technical and economic considerations, the decision was taken to line two 1.4km lengths of the twin DN 1200 pipelines with PE using Subterra's patented Subline close-fit lining system.
In the Subline process thin-walled PE pipes are fused into string lengths to suit site conditions (in this case approximately 350m) and are then folded at ambient temperature on site into a heart shape using the specialist Subline forming equipment.
The folded pipe is held in shape by use of temporary restraining bands and then inserted into the existing main to be lined using conventional slip-lining technology.
Winching loads are low - as a result of the greatly reduced cross sectional area - and well below 50% of the yield strength of the PE pipe. Once inserted, the PE liner is reverted to form a close-fit with the existing main by pressurising with water at ambient temperature.
For this project, standard PE-80 grade PE pipe was used. The dia was 1172mm with an SDR (Standard Dimensional Ratio) of 61 giving a wall thickness of approximately 20mm.
The pipe was produced by Hohn in Germany and supplied by Polva NL in lengths of 24m in order to minimize on-site welding.
The lining was installed in 8 sections by Subterra's Belgium-based Benelux licensee, Etersol. On-site technical support was provided by the Subterra team.
Each lined section was between 280m and 360m from insertion to reception pit. The lining work was carried out over an eight week period finishing in July 1999, and included lining through a syphon in which the line of the pipe deviated some 900mm over a 24m length.