MONITORING OF ENGINEERING GEOLOGICAL AND SEISMIC PROPERTIES OF SOILS DURING CONSTRUCTION AND OPERATION OF OLYMPIC FACILITIES (SOCHI, IMERETIAN LOWLAND)    

Trifonov B.A.¹, Milanovskii S. YU.^1,2, Nesynov V.V.¹

¹Sergeev Institute of Environmental Geoscience RAS (IEG RAS) Ulansky per. 13, bld. 2, Moscow, 101000
² Sсhmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia

We analyzed the nresults of experimental studies of temporal changes in seismic conditions for typical soil complexes unfavorable in engineering and geological terms on Imereti Lowland during the construction and operation of Olympic facilities. It is shown how seismic conditions have changed for soils (category II–III) under the influence of technogenic factors after the construction in 2011–2014 and subsequent operation of Olympic facilities. For this territory, a number of seismic microzoning (SMZ) maps was built with changing seismic conditions depending on technogenic factors from 1986–1996 (start of work in the areas of future development in Sochi) till 2014–2021 (the end of construction and operation of the main Olympic facilities). According to our research results, the Imereti Lowland was classified as a territory with seismic intensity (I) more than 9 (category III) in 1986–1996. In the areas of expected Olympic facilities location (after engineering preparation of this territory for construction), the areas with soils of II–III categories with seismic intensity I = 8.5 and 9 with a frequency of 500 and 1000 years, respectively (for important structures) were mainly distinguished in the map of SMZ (2007). There are also some areas with primary soils (category III) with seismic intensity of 9 and more (9*). The studies in the territory of constructed and planned Olympic facilities have revealed the changes in the initial seismic properties in a number of areas with soils of category II–III. During 4–5 years, under the influence of technogenic factors on the soil massif, the seismic intensity increased by 0.5–0.7; and soils became closer to category III. In addition, the risk of possible seismic liquefaction of soils rose there. In our new SMZ map (for the years after 2014), more sections of III and II categories are outlined with seismic intensity of 9 (9 *) and 8 (8.5), respectively, as compared to the map for 2007. To reduce the negative impact of technogenic factors and improve seismic conditions on the territory of the Imereti Lowland, it is proposed to create an artificially prepared foundation for the construction. On dynamically unstable soils, where subsidence may intensify, in order to improve properties of the foundation soils and to reduce the risk of seismic liquefaction, it is proposed to stabilize soils by creating an artificial pile foundation in addition to lowering of the water level. Examples are given of the artificial improvement of the soil massif created by piles foundations of buildings under construction. It is shown that the creation of a pile foundation for strengthening soil massif of category III reduces the maximum accelerations A_max by 25–30% from the close zones of the origin of earthquake (ZOE), generating high-frequency earthquakes, and by 10–14% from remote Sukhumi ZOE zone, which generates low-frequency earthquakes.

Key words:  gorge, river valley, erosion-accumulative cycle, terrace, terrace row, orogen

REFERENCES

1. Balabanov, I.P., Gey, N.A. Istoriya razvitiya Imeretinskoi  laguny v mezhdurech’e Mzymta-Psou [The history of the development of the Imeretian lagoon (Lowland) in the interfluve of the Mzymta-Psou]. Chernomorskii region v usloviyakh global’nykh izmenenii klimata: zakonomernosti razvitiya prirodnoi sredy za poslednie 20 tys. let i prognoz na tekusyhchee stoletie [The Black Sea region under the global climate change: patterns of development of the natural environment over the past 20 thousand years and forecast for the current century]. Moscow, Geographic Faculty of the Moscow State University, 2010, pp. 25-41. (in Russian)
2. Golovanov, A.M., Pashkov, V.I., Revo, G.A. Opyt zakrepleniya prosadochnykh i nasypnykh gruntov osnovanii fundamentov zdanii i sooruzhenii tsementatsiei [Experience in cementation grouting of collapsible and fill soils in the basement of buildings and engineering structures]. Collection of scientific papers. Rostov-on-Don, Rostov PromStroyNiiProekt Publ., 2004, pp. 68-71. (in Russian)
3. Il’ichev, V.A., Kurdyuk, A.Yu., Likhovtsev, V.M. Metodika otsenki vliyaniya iskusstvennogo osnovaniya na intensivnost’ i spektral’nyi  sostav seismicheskikh kolebanii [Procedure of evaluating the artificial foundation influence on the intensity and spectral composition of seismic vibrations]. Osnovaniya, fundamenty, i mekhanika gruntov, 1992, no. 6, pp. 28-30. (in Russian)
4. Mindel, I.G., Trifonov, B.A. Izmenenie seismicheskikh svoistv gruntov v osnovanii zdanii i sooruzhenii vo vremeni, a takzhe posle ikh uluchsheniya metodami inzhenernoi podgotovki [Changes of seismic properties of soils at the base of buildings and constructions in time, as well as after their improvement by engineering preparation methods]. Promyshlennoe i grazhdanskoe stroitel’stvo, 2003, no. 10, pp. 35-37. (in Russian)
5. Ozmidov, O.R. Otsenka riska seismicheskogo razzhizheniya gruntov geologicheskogo osnovaniya ob’ektov olimpiiskogo stroitel’stva v g.Sochi [Estimation of the risk of seismic liquefaction of soils in geological foundation under the Olympic engineering structures in Sochi]. Vestnik RAEN. Inzhenernaya geologiya, 2014, no. 1, pp. 48-54. (in Russian)
6. Ratnikova, L.I. Raschet kolebanii na svobodnoi poverkhnosti i vo vnutrennikh tochkakh gorizontal’no-sloistogo pogloshchayushchego grunta [Oscillation calculation on the free surface and in the internal points of a horizontally layered absorbing soil]. Seismicheskoe  mikroraionirovanie [Seismic microzoning]. Moscow, Nauka Publ., 1984, pp. 116-121. (in Russian)
7. Ratnikova, L.I. Metod rascheta seismicheskikh voln v tonkosloistykh sredakh [Method for calculating seismic waves in thin-layered media]. Moscow, Mir Publ., 1973, 124 p. (in Russian)
8. Ratnikova, L.I., Levshin, A.L. Raschet spektral’nykh kharakteristik tonkosloistykh sred [Calculation of spectral characteristics of thin-layered media]. Izv. AN SSSR. Fizika Zemli, 1967, no. 3, pp. 41-53. (in Russian)
9. Sevostyanov, V.V., Mindel, I.G., Trifonov, B.A. Kolichestvennye kharakteristiki seismicheskikh vozdeistvii na ryade srtoitel’nykh ob’ektov v g. Sochi po dannym issledovanii poslednikh let [Quantitative characteristics of seismic impacts on a number of construction facilities' in Sochi according to recent studie]. Seismostoikoe stroitel’stvo. Bezopasnost’ sooruzhenii, 2005, no. 5, pp. 71-74. (in Russian)
10. Ulomov, V.I. Veroyatnostno-determinirovannaya otsenka serismicheskikh vozdeistvii na osnove kart OSR-97 i stsenarnykh zemletryasenii [Probabilistic-deterministic assessment of seismic impacts based on OSR-97 maps and scenario earthquakes]. Seismostoikoe stroitel’stvo. Bezopasnost’ sooruzhenii, 2005, no. 4, pp. 60-69. (in Russian)
11. Bardet, J.P., Tobita, T. NERA: A computer program for nonlinear earthquake site response analyses of layered soil deposits. University of Southern California. Deportment of Civil Engineering, January 2001, 44 p.