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Earthquake properties that affect the liquefaction of a soil are described with one parameter known as the cyclic stress ratio (CSR). The stress reduction coefficient parameter accounts for the flexibility of the soil profile. The previous proposed equations could be used in routine engineering practice so long as the simplified (rd) was used to assess CSR, but could be unconservative if used in sites with complex soil layers or in design of vital facilities such as dams, hospitals, bridges and ….
This research presents the results of studies in Babol city to develop, depth reduction factor (rd) based on equivalent linear analysis of study area for evaluation of cyclic stress ratio. As a part of microzonation study for the Babol city a total of 35 boreholes have been drilled in 35 km2 of the research area. The depths of these boreholes ranged about 25 to 35 m. SPT blow counts were taken in each 2 m depth. Many geophysical investigations, generally 35 downhole logging surveys, are carried out in 35 mentioned boreholes for generation and measurement of shear wave velocity. Based on these analyses, the (rd) diagrams and equations are developed for each mentioned zone.