APPLICATION OF THE COMPLEX OF GEOPHYSICAL METHODS TO INVESTIGATE THE K-25 RESERVOIR EARTH DAM IN THE REPUBLIC OF KAZAKHSTAN

Abstract

The relevance. The safety problems of dams used for agricultural land reclamation are acute in the society. Their destruction leads to the great economic and environmental damage. Their monitoring by the non-invasive geophysical methods takes a worthy place for solving this problem. The geophysical methods allow obtaining the information about the object of research cheaply and promptly and complete the traditional geotechnical methods. During the dam operation water seeps through its body, around the spillway structures, as well as in the near-side part, which leads to the formation of erosion zones. This process is accompanied by the changes in the physical-mechanical properties of rocks, which can significantly influence the stability and safety of construction. The timely detection at an early stage of such changes by the geophysical methods is important to take the preventive measures and preventing the disasters. The aim of the study is to substantiate rational set of geophysical methods, their testing on the earth type hydraulic structures and evaluate their informativity when determining the structure current state. Object: erosion zones of the K-25 reservoir earth dam in Kazakhstan. Methodology: field study, processing and interpretation of received data; identification of erosion zones, related to humidifying, by the resistance, polarization, dielectric penetrability parameters; drawing of the initial engineering-geological section of construction; substantiation of regime supervision by the self-potential method; mapping of infiltration zones and its direction at the different degrees of reservoir filling; allocation of decompaction zones and their evaluation by the longitudinal and lateral wave data; complex interpretation of results. Results. The authors have developed the diagnostic technology of earth dam physical state according to the geophysical data in the conditions of the Republic of Kazakhstan. The methods of dipole electric sounding of evoked polarization, vertical electric sounding and ground penetration radar sounding have shown the high efficiency at revealing the sites with the increased water permeability. The information content of geoelectric parameters was assessed for the identification of the flowing water bearing zones and their mapping in the plan. The authors carried out the analysis of complicating factors when using these parameters. According to the data of vertical electrical sounding, the detailed distributions of electric resistance, testifying to the essential inhomogeneity of dam body in this parameter, were obtained. The engineering-geological cross-sections, which may be considered as the starting models for monitoring dam permeability, were made based on the complex data. The area electrical survey by the self-potential method at a variant of regime observations proved to be effective at the revealing of water filtration zones. The longitudinal and transverse seismic surveys were quite effective to study the structure of dam and identify the weakened zones, where filtration may take place. The results of seismic survey correlate quite well to the results of electric potential dispersion when assessing the filtration conditions. According to the results of experimental-methodical works it is possible to conclude, that it is expedient to use the electrical survey for the primary estimation of dam condition, as the most express method. For more detailed study of structure, it is necessary to apply self-potential method and seismic survey on the longitudinal and transverse waves.