THE RELATION BETWEEN THE SEISMIC AND GEOMECHANICAL MODELS

Abstract

The subject of research in this paper is the correlated relations between the seismic and geomechanical characteristics of the medium. A special interest of analysis is made on rocks, which cover a wide area in the Republic of Macedonia, especially in the western part. Field seismic tests are performed at specific locations that define Vp and Vs velocities. At the same locations, geomechanical and engineering-geological research is carried out. Presented dependence between Vp and Vs velocities and geomechanical parameters of the medium: Е - Young's modulus of elasticity, G - shearing modulus and ν - Poisson coefficient. Dependences of these paramform Vp and Vs velocities are calculated, or an attempt is made to assess the geomechanical parameters through analysis of seismic speeds. Qualitative assessment is made on the degree of dependence of seismic velocities Vp and Vs with RQD, RMR and Q parameters of carbonate massifs, as well as with φ - angle of internal friction and с - cohesion of material. Model of the rock masses is relatively simpler than the soil model, where significant influence has subsurface water and many other physical phenomena that are not present in the rock masses or their values are negligible. Any geophysical method is based on measurements of certain parameter, for example, gravity measures the force of gravity or appropriate earth acceleration, or geomagnetism measures the intensity of the magnetic field etc. Seismic methods are based on determination of the propagation velocity of longitudinal Vp and transversal Vs wave, or measurement of the velocity of propagation of the elastic waves in the ground. From engineering point of view, of interest is shallow seismic which exploring goes up to more than 100 m. The usage of geophysical methods, especially seismic, has an irreplaceable role in defining geomechanical parameters of the environment. The best results are obtained if geophysical methods are combined with research drilling and laboratory measurements of the taken samples, or geophysical methods define the locations for exploratory drilling. Based on the field research and laboratory testing, the conditions of the terrain as a natural environment are defined, the soil layers are defined according to the depth of the investigated location, ie the possible interactions between the natural environment and the future construction are predicted. In this phase of the research, the geological structure of the terrain was analyzed by defining the basic parameters of the separated lithological members required for the design phase. During the preparation of the work, a database of knowledge from the geological and geotechnical sciences was used, using modern methods of interpretation of data, own experiences from research on a range of objects and standardized methods of research and testing.