e-mosty March 2019 Long Span and Multiple Span Bridges | Page 26

Figure 6:
Seabed profile at bridge location
At the Central Pylon location at Roca Remolinos,
the top geo-unit termed as Caprock from ground
level to around El. -39.0 MSL, is a volcano-
sedimentary conglomerate with heterogeneous
clast size and nature, and very variable clast/matrix
proportion.
It is composed of brecciated quartz, highly silicic
glass (with variable contents of alkalis), plagioclase
components and small proportion of clay minerals
in the interstitial fine-grained cement.
The geo-unit just below the Caprock formation,
down to about El. -73.0 MSL is mainly composed of
silty sand to sand with silt. The drilled shafts
supporting the Central Pylon are tipped in this soil
unit at El. -50.0 MSL approximately.
Bedrock was not encountered at the bridge site
within the depths of the geotechnical drilling
programs.
CPC conducted a geotechnical exploration
program to develop final foundation design
parameters.
Three
previous
geotechnical
campaigns were performed by the owner in 2000,
2001 and 2005 at South Bank, Central Pylon and
North Bank locations.
CPC carried out a supplementary geotechnical
campaign in 2015 for the detailed design phase,
which included field drilling up to 100-meter
depth, standard penetration tests (SPT) and
pressuremeter tests (PMT), geophysical PS logging,
piezometer installation, and a comprehensive
laboratory testing program.
The laboratory tests included the index tests,
unconfined compressive strength tests, triaxial
tests, cyclic triaxial tests (seismic and fatigue),
resonant column tests, oedometer tests, chemical
tests and mineralogical analyses.
Following the geotechnical investigation program,
CPC developed the design parameters for shear
strength, soil deformation and consolidation,
unconfined compressive strength, shear modulus
and damping ratio, drilled shaft skin friction and
end bearing resistance.
MAJOR PROJECT ELEMENTS
PYLON FOUNDATIONS
In-water foundations for the North and Central
Pylons utilize 2.5 meter-diameter drilled shaft
foundations along with permanent steel casings
embedded at the top in the pile caps and
extending into excavations drilled into the sea
floor.
The pile casing participates with the longitudinal
pile reinforcing steel cage to resist lateral loads
resulting from seismic, vessel impact, and other
design demands.
Casings thickness varies with design demands, and
the casing segments are welded together at the
site.
Aside from addressing structural demands, the
steel casings allow construction of cast-in-place
reinforced concrete piles in water depths of up to
25 meters.
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