Seismic soil classification using a new standard proposal and comparison with the current standard for sites located in Reñaca and Concón

Abstract

In Chile, to seismically classify a site where a structure is to be founded, the indications of the Chilean design code (NCh433 and DS61), have to be fulfilled. It is a requirement to have the average soil shear wave velocity of the upper 30 m of the site (Vs30), and laboratory or in-situ test results related with soil resistance such as:unconfined compression strength (qu), normalized standard penetration test resistance (N1) and/or soil undrained shear strength (Su). In the new classification proposal system (prNCh433, 2018), classification parameters are those that are related to seismic response at the ground surface of the site: Vs30, and the predominant soil period (Tg) estimated using the H/V spectral ratio (method of Nakamura). On this article it is compared the classification requirements of the Chilean standard with main design codes and standards in the rest of the world. Also, fundamental periods of soil obtained from measurements carried out in Reñaca and Concón area, are used to seismically classify sites where soil mechanics reports are available. The classifications are undertaken with the new proposed classification standard and comparisons are made with the current classification. As part of this work, it is analyzed whether the sites maintain or change their seismic soil classification and the type of change they undergo. Finally, soil parameters that are determinants for the obtained soil classifications are identified.