Foundations and basements construction of a shopping mall on the soft soils of Bogotá

Luis F. Orozco, Marcela Salcedo

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Deep Foundations

ABSTRACT: The lacustrine soft soils of Bogotá imply great geotechnical challenges for the foundations of tall buildings as well as for the excavations of more than two underground levels. This paper presents the foundations and excavation system of a large shopping mall with three basements and four stories high. The TITAN Commercial Center is being constructed at the intersection of Calle 80 and Avenida Boyacá, north east corner. There is a description of the geotechnical characteristics of the highly plastic soft clays. There is also a description of the mat and pile foundation and construction systems, which include open pit excavation to 4.5 m depth, then the construction of piles, retaining walls, belt and strut slabs, and then open pit excavation to 9m depth in stages. Also the excavation to 11.5 m under the structure is described. The paper includes conclusions and instrumentation results.

RESUMEN: Los suelos blandos del depósito lacustre de la sabana de Bogotá implican grandes retos geotécnicos, tanto para la cimentación de edificios de gran altura como para la ejecución de más de dos sótanos. En este artículo se presenta la cimentación y sistema de excavación de un centro comercial de grandes dimensiones con tres sótanos y cuatro pisos de altura que se encuentra localizado en la esquina nor-oriental del cruce de la Calle 80 con Avenida Boyacá, en la ciudad de Bogotá. Aparecen aquí las características de los suelos arcillosos muy blandos y de alta plasticidad, se describe la cimentación con placa y pilotes y el sistema de construcción que incluye una primera excavación a 4.5 m de profundidad, muros de contención tipo pantalla y pilotes, placas puntal y placas cinturón y luego la excavación por etapas a cielo abierto hasta 9 m de profundidad y también se presenta la excavación de 9 a 11.5 m bajo la estructura. Se incluyen igualmente los resultados de instrumentación y las conclusiones respectivas.1. INTRODUCTION Bogota™s soft soils imply very important geotechnical challenges. It is a quaternary lacustrine clay deposit over 200 m thick, formed by highly plastic soft clays with a low over-consolidation ratio. The foundation of buildings, with 2 to 5 underground levels, usually includes a mat foundation to avoid bottom failure and support water pressures, as well as piles needed to carry a substantial portion of the load, work in tension for low weight portions of the building and support the loads during construction with an up-down construction method. This paper deals with the problems, due to the very soft soils, for the construction of a large shopping mall (230 x 130 m) with three underground levels and in most of the area only three to four stories above ground level. The TITAN Commercial Center is being constructed at the intersection of Calle 80 and Avenida Boyacá, north east corner. The description of the geotechnical properties to a depth of 50 m is presented, followed by the account of the foundation and construction methods. The foundation includes a mat foundation supporting an upward pressure of 6 T/m² or 59 KPa (bottom failure as well as water pressures) and cast in place friction piles with a length of 23-28 m. The construction method includes first a large excavation to 4.5 m depth, covering the foot print area, then the construction of piles and slurry walls. The piles are constructed to -11.5 m elevation (foundation grade level), except for those necessary to support peripheral wale slabs and two slabs as struts across the area, all of which work to support the large horizontal pressures on the retaining walls. The excavation proceeds as an open pit in the three central areas to a depth of 9.0 m. From this depth the construction includes caissons to reach the head of the piles, columns and the upper structure, as well as the excavation under the structure to 11.5 m depth (up-down construction). There is a description of the geotechnical instrumentation program; which is a priority in this type of job. Also there is a description of some of the problems that had to be solved during excavation. Among the main conclusions are the importance to build

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