Difficult Excavations and Foundations for Buildings on Soft Soils in Bogotá

Bogotá is located on a 230 m thick soft clay deposit, with high water table. The foundation of buildings, with more than 2 underground levels and 10 stories, generally consists of a mat-pile system constructed with an up-down method (i.e., basement excavation and structure construction advance simultaneously). The up-down method used in Bogotá takes care of properly supporting large earth and water pressures, and minimizing movements of nearby and bottom soils. Another essential complement of the method used in Bogotá is the system of wells for pressure relief within the site and the re-injection wells for compensation of water table drops outside the site, reducing nearby settlements. This paper describes: (i) Bogota's subsoil conditions, (ii) the importance of instrumentation, (iii) geotechnical challenges encountered during excavation, (iv) the up-down construction method used, and (v) two case histories: Cusezar's tower and Santa Ana's tower.