Experience of using seismoacoustic methods for a detailed modeling of geological environment at design of high criticallity objects of nuclear construction

Abstract

Engineering surveys for the design of facilities with high criticality rating require a switch from methods with discrete assessment of environmental parameters (drilling and static / dynamic sounding), to methods that allow to obtain these values continuously in а massif. The most efficient way to solve this problem is by performing crosshole seismic tomography (CST). The article presents the results of CST during geophysical studies at the site of projected nuclear power plant (NPP). Four cross sections were obtained as a result of survey at distances from 24 to35 metersbetween the boreholes. Requirements for the boreholes preparation are specified in article, along with description of equipment for seismic signals excitation and registration, the examples of seismic records (gathers), methods of analysis and data processing are also shown. The velocity sections for compressional and shear waves obtained as a result of tomographic inversion are presented. The values of dynamic characteristics of soil properties (Young modulus, shear modulus, Poisson ratio) and their distribution in the inter-well space were calculated with the use of data on the soil density of the massif. Also, the article shows the result of applying the technique of incident and reflected waves fields allocation, which were obtained as a result of seismic cone penetration test (SCPT) to depths of 20–30 meters aiming to get detailed geological cross-section.