On March 25, 2008, the Geotechnical Group held a lecture at the CUNY Graduate Center Recital Hall in Manhattan focusing on the reconstruction of the ancient library of Alexandria, which was destroyed more than 2,000 years ago and rebuilt in the late 1990s. Amr Ragy, currently chief engineer and estimator for Treviicos Corporation and formerly senior geotechnical engineer for the Alexandria Library project, gave the lecture to the group. The sponsor for this lecture was Treviicos Corporation.
Presented by: Amr Ragy, Chief Engineer and Estimator, Treviicos Corporation, Boston, MA
Mr. Ragy began the lecture by briefly describing the history of the library as the beacon of learning and scholarship for the ancient world and the architects’ dreams for reconstructing it on the original site adjacent to the Mediterranean Sea. The new library construction was to consist of three structures: the library building, the planetarium, and the bridge. The foundation construction for the library was carried out by RTA, a tri-venture of Rodio, Trevi Group, and the Arab Contractors in conjunction with the Hamza/Snohetta Consortium.
The presentation focused on the construction of a state of the art diaphragm wall system, bored piles, the reinforced concrete raft, jet grouting, and dewatering for the library building. The library building required the design and construction of a complex circular diaphragm wall 115 feet deep to permanently retain the adjacent soil and water loadings. The freestanding height of the slurry wall was 46 feet and the diameter of the wall system was 525 feet. Mr. Ragy discussed the extreme nature of this diaphragm wall construction which necessitated special T-panels, continuous horizontal reinforcement, large corner stiffener elements, and jet grouting to reduce earth pressures in critical areas. The continuous horizontal reinforcement was the most challenging part of this slurry wall in that canvas panels and steel plates were used to act as bulkhead forms to limit concrete flow. The sequence of panel construction and slow placement rates during concrete pours were the keys to success in this operation. Jet grouting was used to stiffen the wall system in the corner areas where the circular wall transitioned to a straight wall section. Mr. Ragy reported that over 40,000 cubic yards of jet grouted soils were created for this purpose.
The foundation for the library building consisted of 40 inch (1 meter), 48 inch (1.2 meter) and 60 inch (1.5 meter) diameter single and double-underreamed bored piles and a large reinforced concrete mat. The bored piles were used to provide support for large compression and tension loads. Mr. Ragy explained that the large tension loads were a result of the asymmetric structure shape and the depth of the foundation below the static groundwater levels, which generated tremendous hydrostatic uplift forces. Base grouting was employed for to improve the base resistance under compression loading. The proof tested capacities of the bored piles were 5,600 and 1,350 kips under the compression and tension test loads. Extended creep testing was performed by the contractors for periods of 15 to 38 days.
Mr. Ragy described many of the other critical points of the foundation construction for this structure. The deformation of the circular slurry wall during and after construction was important because of the shape of the excavation, depth, and permanent nature of the wall. The measured deflections were found to be acceptable and compared reasonably with those predicted by 3D numerical methods. The waterproofing of the entire below grade foundation structure was complicated by the number of penetrations of the membrane by the bored piles. Corrosion protection of the slurry wall was provided by using a very dense concrete mix, large cover requirements, sacrificial anode ladders, and an extensive electrical resistance monitoring program.
Following a number of questions from the audience, Mr. Ragy was presented a Golden Apple from Geotechnical Group Chairman Terry Holman in appreciation for the lecture.