I would like to describe the deflection measurements that I made while I was still with the Geotechnics Division of the Building Research Station; the subject for a paper shortly to appear in International Water Power and Dam Construction.336. The interest of the Building Research Station in Marchlyn dam stemmed from the fact that it is amongst the first British dams to use an upstream asphaltic membrane. As part of our study of the behaviour of dams, aimed at an improved understanding that can lead to design improvements, it was felt desirable to measure deflections of the membrane under water load, particularly since, as reported by Dr Charles and mentioned in the Papers, laboratory tests had been carried out in our 1 m dia. oedometer on rockfill samples.337. In preliminary discussions with Mr Carlyle, I had proposed the use of an inclinometer in tubes laid just under the membrane, but understandably this had been turned down because of a risk that trenches made for the tubes could form weaknesses: settlement of the backfill could produce undesirable strains in the membrane. It was therefore decided that measurements could be made on the surface of the membrane. Freed of the constraint of a small access tube and the need to design a special inclinometer to work on the 1 on 2 slope, a trolley was developed to run on rails and carry a standard inclinometer in a vertical position.338. Because the waterproof membrane consists of one 80 mm thick layer, it was not feasible to put bolts through it for attaching the rails, so sub-frames were used. These were placed on the surface of the completed membrane at the major section of the dam and buried in an additional layer of asphalt by the paver straddling over the line of frames. Tapped holes in the frames were then exposed by coring through the asphalt and fitted with threaded stubs to carry the rails just above the surface of the asphalt. The space round the stubs was filled with hot bitumen and the whole surface covered by seal coat before the rails were attached.339. The trolley was made with a 2 m gauge length between wheel centres and the rails had stainless steel inserts at 2 m centres. A length of inclinometer tube was built into the centre of the trolley so that it would be vertical when the trolley was on the 1 on 2 slope. A special cable containing a straining wire as well as the conductors was used to lower the trolley from a winch screwed to the floor of a side-door van driven on to the crest. The inclinometer had a half metre gauge length and gave offset readings to 0.1 mm. It was turned round in its tube to overcome zero errors, and four runs were made, two with the inclinometer on each face. By summing these four readings, the offset values of the 2 m long trolley were obtained.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.