For both new buildings and extensions in developed areas, the surrounding building density and existing nearby underground structures can impose effective limits on the use of traditional digging to create a foundation. In such cases, the top-down system could be an option, as it reduces the area that has to be dug up, cuts the time needed and related problems, and safeguards the existing structures. A project by archiNOW! and Antao Progetti in Gualdicciolo, in the Republic of San Marino, had to deal with a rather dilapidated area when building a new bank branch with a large underground section to hold a 200-seater auditorium below a double-floor underground parking lot. The morphology and shape of the site were central to the architects’ decision to use a top-down system. This created the question of how to waterproof the underground
structures, which had to be built in parallel with the structural work, moving from the top to the bottom. To guarantee perfect water tightness for the basement levels, the continuity of the waterproof layer is especially important, particularly in those critical sections where the ends of the floors slabs are anchored to the excavation bulkheads. Mapei’s Technical Service was involved in the waterproofing design and creation stages, including on-site consulting. In this instance, Mapei provided Mapeproof, a safe, effective solution based on natural sodium bentonite, a clayey mineral that originates from the alternation of volcanic ash, which expands when damp. The Mapeproof system consists of various products including a waterproof fabric (for vertical and horizontal use), Mapeproof Mastic grout, Mapeproof Seal, nails and Mapeproof CD polyethylene washers. In many cases, the waterproofing was done directly on site, such as for the foundation pads with pile heads, the tubing for the geothermal system, the elevator wells and the internal tanks. This is further evidence that this truly is a comprehensive system and another demonstration of the importance of technical experts and architects working closely together and drawing on all their experience and expertise to ensure the actual solutions to individual problems.
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