Progress Wendover Arm Good progress by Wendover Arm Trust on profiling / lining the channel, coping with a coal tar problem, and solving the mystery of the disappearing pipe Grand Union Wendover Arm
next inspection pipe hole about 30m beyond. We started excavating around hole and eventually found signs of the trench. Further digging back towards our work area showed that the trench soon disappeared. How could this be? Further delving was enough to find the top of the pipeline and we could now see which direction it was running. We also found that excavating with our 13-tonne machine was difficult due to the very hard (almost like limestone) chalk layers. It would seen the team 100 years ago found it so difficult to carve through, that they decide to tunnel under the rock! It must have been very risky to hand dig some 30 m under the rock, especially as what appeared to be a softer layer was more likely to drop from the roof... Mystery solved, the hole was filled in and it was back to the concreting. This con-
August working party: Having now finished the brick work on the towpath side on the old swingbridge site at Bridge 4, “all we had to do” was to make a mirrored version on the offside. The existing structure condition was found to be very poor and most of the work done was demolishing the brick work and excavating down behind the bricks to give a clear working area. Rebuilding could now begin. On to the main task of continuing the concrete pipe capping and roadway in the canal bed. [see explanation of ‘pipe capping’, right ...Ed] Excavation continued, following the “trench” infill that resulted from the pipeline being installed under the bed at the turn of the century. The concrete layer is 150mm thick and reinforced with steel “rebar” sheets. We have chosen to Pipe capping: an explanation make it wider than strictly needed to just protect the Bentomat liner should The Wendover Arm was built primarily as a feeder to the pipe ever collapse in future. This bring in water from springs near Wendover to feed the will allow the machines to run on a Tring summit of the canal’s main line – but it suffered concrete “road” and thus avoid all the from long-term leakage problems as a result of the issues with mud churning and subseporous chalky soil it passed through, and this led to its quent volunteer risks. It also allows eventual demise as a navigation, and to the worst the dumpers to run inside the wooden section being drained many years ago. formers to get the concrete to where it That’s the length that’s now being restored: it is needed when casting the road. has an 18-inch glazed clay pipe installed underneath, This all went well until the line of buried in the canal bed, to carry a feed to allow water the trench “disappeared”. We think the from Wendover to still reach the pumping station at trench was originally dug by use of a Tring (and from there to the Grand Union main line) steam shovel or similar, due to its after the canal had been drained. Due to the age of the regularity and depth. The clay pipe pipe (which is now abandoned and blocked), as part with mortar joints wouldn’t have lent of the channel restoration and waterproofing work, itself to sharp bends so where did the protective measures must be taken to avoid damage to pipe go? We also found that the old the new lining system if the pipe ever collapses under the coal tar lining was intact across the restored canal. Therefore the pipe is being uncovered, a canal bed, the coal tar having being section at a time, and a concrete ‘raft’ or capping is being put there long before the pipeline, as a installed on top of it to provide that protection. final attempt to make the channel That capping also forms a temporary access waterproof before the canal company road for machinery to get to and from the worksite, gave up and piped the water. before the new channel is built on top of it, incorpoFaced with this puzzle we went rating a waterproof Bentomat (bentonite clay matting) to the only place where we knew the membrane to avoid the leakage problems recurring. pipeline would be and that was the
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