e-mosty March 2019 Long Span and Multiple Span Bridges - Page 25

Figures 3 and 4: Wind Tunnel Tests of the Central Pylon Vessel impact was another significant design consideration. The ship collision study was carried out following the recommendations given in AASHTO LRFD Bridge Design Specification, 6th Edition, 2012. The study included a detailed AIS (Automatic Identification System) traffic analysis, it addressed the most relevant accident scenarios and determined the probability of aberrancy (PA) based on an analysis of historical data. According to AASHTO LRFD, this is equivalent to conducting navigational simulations. The results of the study confirmed that the return period of bridge collapse due to ship collision was greater than 10,000 years. In conclusion, the risk level under ship collision was found to be sufficiently low. Two different geomorphologies are present near the project site. The irregular topography of the Chiloe (South) side is consistent with a typical glacial geomorphology. On the continental (North) side, the morphology is much regular with plateau-like aspects corresponding probably to quiet sedimentary deposits conditions (lacustrine /outwash). Stratigraphy at the Pylon and Anchorage foundation locations on the North and South channel banks is characterized as follows:    SITE GEOLOGY AND GEOTECHNICAL STUDIES The project site geology is primarily the result of historic advances and retreats of glaciers from the nearby Andes Mountains.  Soils from ground level to around El. 0 MSL are mainly silt, gravely sand and sandy silt. A cementitious soil layer called “cancagua” is only found in the south bank approximately from El. 0 MSL to around El. -10 MSL. The underlying soil layer is recognized as silty sand, silt or sand with silt, occasionally gravel and lean clay to around El. - 82.0 MSL. The lowest soil layer encountered down to the end of boreholes across the project site is silt or silty sand with isolated lean clay. Figure 5: Geotechnical Strata 1/2019