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