Deep excavations associated with the construction of underground parking garages for major corporate buildings create significant challenges for geotechnical engineers, especially when the subsurface material consist of non-controlled fill. This paper provides a detailed description of a project located in Santa Fe, Mexico City, Mexico, where two corporate towers with 26 and 12 stories and 8 basement levels were built on a 1970s landfill site. Based on the maximum depth of excavation and local restrictions on deformations for major road arteries located in close proximity to the project site, the retaining system selected for the project consisted of a diaphragm wall reinforced with post-Tension anchors. In addition to geotechnical drilling and sampling, results of three full scale pull-out test completed at the north end of the project site are discussed. From the load tests, cable elongations were recorded to be less than 1% of the bonded length of the anchors.