FIELD SURVEY OF SELF-HEALING OF CRACKS IN THE IMPERVIOUS ELEMENT OF BORED CLAY-CEMENT CONCRETE PILES

The article contains a description of the methodology and the results of field experiments on self-healing in the impervious element of bored piles filled with clay-cement concrete at the site of temporary shoring of excavation pit of the main structures of Nizhne-Bureyskaya HPP. The results of the experiments allowed us to determine the suitability of local sand from the quarry №5 for self-healing of cracks. Recommendations for quality control of the sandy soil, placed into the transition zones of the dam, were developed. Subject: field studies of colmatization of through cracks in clay-cement concrete diaphragm of earth dams at the site of temporary shoring of excavation pit of the main structures of Nizhne-Bureyskaya HPP. Research objectives: determine possibility of application of the sand material, existing in local quarries, as a contact layer that provides self-healing of cracks in case of their creation in the body of the clay-cement concrete diaphragm of the earth dam of Nizhne-Bureyskaya HPP in the process of its operation. Materials and methods: field experiments were conducted on a transverse shoring of the excavation pit of the main structures of Nizhne-Bureyskaya HPP. Conducted experiments consisted in self-healing of artificial cracks by sandy material arranged in clay-cement concrete piles of temporary shoring, for which a cylindrical cavity for accumulation of sandy material was created in the body of the pile by drilling. At the bottom of the pile from the pit, artificial holes were created for self-healing. Results: it was experimentally confirmed that when using sand from the quarry № 5, the through cracks in the diaphragm of the dam of Nizhne-Bureyskaya HPP will be completely colmatized by the soil of the healing layer located in front of the top face of the diaphragm. The sand from the quarry № 5 can be used as a material of the contact layer that provides self-healing of cracks in clay-cement concrete diaphragm of the earth dam, and when it is used, it is necessary to control the recommended granulometric composition of sand and ensure absence of lumps of clayish soils. Conclusions: in the field conditions, we obtained the values of hydraulic gradients at which takes place the self-healing of cracks in clay-cement concrete diaphragm of the earth dam. The requirements to granulometric composition of the contact layer in the structure of the earth dam were clarified. Recommendations were developed for quality control of soil when laying the contact layer of the earth dam.