Vízügyi Közlemények, 1960 (42. évfolyam)

4. füzet - VI. Képek a Föld különböző részeinek vízépítési munkáiról

(61) per cent. The reservoir created by the Serre Ponçon dam belongs to the group of developments with great storage. The earth dam, which attains a height of 125 m is among the highest dams of this type. The dam under construction at Serre Ponçon is built of uniform soil material with a watertight core. The dry method of construction is adopted. Its importance for the regulation of the Durance River is fundamental. The catchment area of the Durance River is 15 200 sq. km, and the regime of the river is highly irregular. The average annual dry-weather flow in July-August is 45 eu. m/sec, whereas the average flood discharge is from 2 to 3 000 cu. m/sec. The highest flood discharge has been recorded in 1886 at 6000 cu.m/sec. For constructing the first dam and reservoir serving the purposes of regulation, the surroundings of Serre Ponçon appeared as most suitable, where the Durance River is joined by its tributary, the Ubaye River and where the wide valley forms a relatively narrow gorge. The first exploratory drillings were carried out as early as 1856, yet the building of the dam was not commenced until 1955. 1 200 million cu.m water can be stored behind the dam, of which live storage amounts to 900 million cum The crest of the dam is 600 m, the greatest width of the foundation is 650 m. The volume involved is 14 million cu.m. The dam rises to 125 m above its fundations over an alluvial subsoil forming a 110 m deep layer. The total capacity of the four vertical-shaft Francis turbines installed at the powerhouse is 360 000, kWs, and they generate in an average year 700 million kWhs of electrical energy. Under normal watersurface conditions the spillway has a capacity of 1 800 cu.m /Sec, which rises to 2 000 cu.m/sec when the reservoir is entirely full. Sealing of the 110 m deep alluvial layer, which forms the subsoil at the dam site, presented a major problem. As a result of laboratory and two site-tests, a watertight curtain was created by grouting extending donw to the bedrock. The curtain is 32 m wide down to 15 m below the foundation then tapers down to 12 m over llie next 24 in, and remains of constant width down to the rock. A wet-ground mortar of clay and blast-furnacë cinders was used for grouting, which was carried out with pressures lower than 5 atmospheres. The grout curtain, which has a volume of about 100 000 cu. m, was created by drilling altogether 17 200 metres of holes, into which 35 000 tons of dry material, 11 000 tons of cinders and 24 000 tons of dryed and ground clay were grouted. After the completion of the grout curtain the permeability of the alluvial layer was found to be 1000 times lower, than in the original state. Suitable material for I he watertight core was found in the vicinity of the dam site. Construction of the relatively thin watertight core required special care. For determining the optimum method of compaction laboratory and field tests were carried out. The necessary compacting effort was found to be 40 000 kg/m. cu. m, and best compaction was attained by using pneumatic rollers rather than sheepfoot ones. Eight passages of the 35 ton pneumatic rollers were required for every 0,30 m thick lift. Protection on the two sides of the watertight core against infiltrating waters was provided by means of two fine grained so-called protective lagers, while the removal of water seeping across the watertight core was accomplished by a network of drainage pipes. For constructing the pervious parts of the dam body, alluvial materials available in the bed of the Durance River were used. Compaction was again carried out by 45 ton pneumatic rollers. Each lift was 0,60 m, and the roller passed four times over each lift. As a protective measure against wave action an 80 m high section of the slope was covered by 100 000 cu.m of stone. The rabble layer is 1 m thick. Aim thick layer of 40 cm diameter gravel was placed also over the downstream slope to protect the latter against erosion by rain. Material is excavated by 2 cu.m draglines, while haulage is by means of 340 HP, bottom dump Euclid saddle type wagons, having a capacity of 19 cu.m. A daily progress of 20 000 cu.m of compacted material has been attained. The necessity of constructing 15 km of new railway track and 50 kin of new highway involved further investment. (Translated by Z. Szilvâssy. с. eng.) 2