Régime transitoire et stabilité du barrage en enrochements de Zlutice

Abstract

The leading particulars of this dam on the river Strela in North-west Bohemia are as follows : - Maximum height above foundations 28 m Crest length 232 m Total volume of structure 212,000 m3 Normal storage level 310.12m Fig. 1 shows a representative cross-section of the dam. The impermeable loess earth core slopes upstream at 1.8 : 1. It is comparatively thin, with a minimum horizontal thickness of 3.20 m and a total bulk of 26000 m3. During construction of the dam the ground water content sometimes exceeded the permissible quantity, in which case 40 kg of lime were added per cubic metre of earth one or two hours before compacting. The granite rock and mica-shale (up to 50 cm size, D10 > 10 cm) fill was vibro-compacted by roller. After the dam went into service in 1969 voids pressure measurements in the impervious curtain with Russian NIS-PD electro-acoustic cells gave values well above the design data, especially after relatively rapid emptying. In view of the possible threat to the stability of the upstream embankment, a mathematical model study was made of pore pressures at critical points for various rates of storage level variation. The report presents a detailed analysis with graphs of pore pressure values measured by pressure cell at varying storage levels and compares these values with theoretical data calculated by the Skempton-Bishop formula, and more generally, data obtained with the aid of Author's mathematical model. As a result of the investigations, operating instructions were compiled which set the following limits to the reservoir emptying rates: 20 centimetres daily between normal storage level and 296.00; 15 centimetres daily between 296.00 and 291.50; 15 centimetres daily beyond 291.50, subject to pore pressures not exceeding the permissible values. Measurements made since these instructions became effective have shown that the dam core has consolidated and that the pore pressures within it have been reduced.