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. 1/2019