Pore pressure in the core of ultra-high earth core rockfill dam at consideration of stress-strain state

In the clayey core of the rockfill dam, pore pressure always appears, which may present a serious threat to the dam safety. Therefore, in the middle of the 20th century, there started the development a theory of clayey soil consolidation in cores of earth core rockfill dams; analytical methods were developed to calculate pore pressure. However, these methods are approximate; they do not permit modeling complicated processes of soil consolidation in the structure. The published data of field measurements at the ultra-high dam of Nurek HPP give evidence about the fact that the processes of accumulation and dissipation of pore pressure in the core soil have a complicated character. At the initial stages of construction, there observed a gradual growth of pore pressure due to the weight of the overlying soil layers. But at the completion stages, pore pressure rapidly decreased, and its values approached the values, which are characteristic for the regime of steady seepage. These effects cannot be explained and simulated by a traditional method of analysis. The rate of seepage is too small to provide occurrence of so rapid processes. Therefore, for study of the processes of pore pressure formation in the core of Nurek dam, a more complicated and accurate method was used, i.e. the method of numerical modeling. Numerical modeling permits joint solving the tasks related to stress-strain state and seepage regime in the structure. Use of numerical modeling permitted us with sufficient accuracy to simulate the pore pressure formation process in the core of Nurek dam, as well as to analyze the causes of the observed effects. It was revealed that the main role in pore pressure formation is played not by the process of water seepage but by the process of the dam stress-strain state formation. Decrease of increased pore pressure due to dead weight loads takes place due to the dam lateral expansion. Increase of pore pressure before the seepage pressure is due to soil deformation under the action of force loads from the upstream side. The considered analytical method of analysis does not take into account the peculiarities of formation of stress-strain state of the rockfill dam earth core, it does not consider appearance of pore pressure from the upstream loads. Therefore, the real processes of the core soil consolidation cannot be simulated with its aid.