GROUND BEHAVIOR IN SYKTYVKAR UNDER SEISMIC
AND MICROSEISMIC IMPACT

V. A. Lyutoev^*, A. N. Vikhot'**

Yushkin Institute of Geology, Komi Scientific Center, Ural Branch, Russian Academy of Sciences ul. Pervomaiskaya, 54, Syktyvkar, 167000 Russia

*E-mail: valutoev@geo.komisc.ru
 ** E-mail: vikhot.anna@mail.ru

Urbanization growth results in the increasing traffic intensity and developing high-rise construction. In particular, in Syktyvkar, the dynamic loading on soils in building foundations and adjacent territories rises. The conception of civil engineering changes, but at present the regulatory standards has not been adopted there yet. Loose soils of thixotropic structure are often unstable to external load; therefore, the study of seismic score increment for local soils, determination of threshold values of soil resistance to local platform dissipated seismicity and microseismic impact from the urban vibration field becomes acute. Samples of glacial, fluvioglacial, and alluvial deposits of the plastic state and granular structure collected in Syktyvkar and its outskirts were tested by vibrodynamic loading with acceleration amplitudes of 0.022–1.9 m/s² corresponding to shock magnitudes of 1.9–6.4 units. According to observations, the effective impact moment for loose soils began already at 5–7 s. The graph of an occurrence frequency of earthquakes was plotted, and the empirical equation was deduced: I(point)=1.3×logT+2.3±0.2. It was established that recurrence of a magnitude 7 earthquake is possible with a 0.5% probability within 50 years, a magnitude 6 earthquake–with a probability of 1% within 50 years, and accumulation of a potential seismic energy near Syktyvkar is quite probable. The functional dependencies of soil behavior have been obtained under loads corresponding to energy earthquakes characteristics. Calculations showed that the earthquake intensity increment depends on the aquifer depth. Horizontal shear stresses arising from a shear-wave propagation are the main stress component upon an earthquake. The vibration field impact on underlying soils of the city covers a longer time period of cyclic loads. In this case, for calculations we propose to take an elastic half-space and for solving a  flat stress problem.

Keywords: coherent and incoherent soils, earthquake, earthquake intensity increment, vibrodynamic loading, PGA, soil compaction, secondary changes

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