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INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. The paper was published in the proceedings of the 17th African Regional Conference on Soil Mechanics and Geotechnical Engineering and was edited by Prof. Denis Kalumba. The conference was held in Cape Town, South Africa, on October 07-09 2019. Innovative foundation design for super-tall buildings T.E.B. Vorster & G. Wojtowitz Aurecon, Pretoria, South Africa ABSTRACT: Innovation has many definitions. For the purpose of this paper the authors lead with the definition stating that for something or some process to be called an innovation, an idea must be replicable at an econom- ical cost and must satisfy a specific need. Innovation involves deliberate application of information, imagination and initiative in deriving greater or different values from resources. In this paper we illustrate the innovative design process applied for the Dubai Creek Tower. Innovation was required due to the immense time pressure and challenging foundation installation depths foreseen using conventional design and construction techniques. By using combinations of total engineering geology approach, efficient parameter choice and choice of param- eter range application, full-scale testing, high-end finite element modelling, modular design and iterative pro- cess between the architect, the structural and geotechnical designers an efficient foundation system for the iconic Dubai Creek Tower was developed, by design. 1 INNOVATION BY DESIGN and founding system such as piled raft or piled foun- dation, to name a few. Innovation has many definitions. For the purpose of The implementation of conventional design meth- this paper we lead with the Business Dictionary’s def- odologies often requires the selection of conservative inition stating that for something or some process to and sometimes empirical ground parameters that may be called an innovation, an idea must be replicable at lead to overly-conservative design, impacting con- an economical cost and must satisfy a specific need. struction time and cost. Conservatism may not be a They go further to state that innovation involves de- driver for buildings of a more conventional height, liberate application of information, imagination and however for super-tall buildings generally in excess initiative in deriving greater or different values from of 300m, construction time, cost and viability of con- resources. In this paper we illustrate the innovative struction methods are some of the most significant design process applied for the Dubai Creek Tower. drivers of project viability. Innovation was required due to the immense time The Council for Tall Buildings and Urban Habitat pressure and challenging foundation installation (CTBUH) has classified buildings from 200 to 300m depths foreseen using conventional design and con- in height as tall, between 300 and 600m in height as struction techniques. By using combinations of total super-tall and mega-tall being in excess of 600m. The engineering geology approach, efficient parameter design of mega-tall buildings requires structural and choice and choice of parameter range application, geotechnical engineers to challenge traditional meth- full-scale testing, high-end finite element modelling, ods for applicability and range of application. Tradi- modular design and iterative process between the ar- tional empirical design approaches cannot necessarily chitect, the structural and geotechnical designers an be extrapolated with a high level of confidence and efficient foundation system was developed by design. designers are required to use more advanced methods of analysis and design (Poulos, 2009). 2 A DIFFERENT APPROACH NEEDED Compared with other buildings, due to the substan- tial building weight, height and slenderness of mega- The process of pile foundation design is well-estab- tall buildings, the design considerations are of a new lished and supported by an extensive range of re- magnitude and complexity. These comprise of large search over decades. However, the science of pile de- vertical loads, moments and lateral loads (in the order sign is still inexact and influenced by many factors of MN and GN); more complex load-sharing within such as geology, loadings, seismicity, installation, the foundation system; soil-structure interaction for groups of piles, cyclic degradation, rigidity of pile cap all loading scenarios; the dynamic response of the structure to wind and earthquake loads and the influ- The design is inspired by a lily flower and minaret, ence of the cyclic nature of these loads on the foun- integrating modern sustainable design with the rich dation; settlements and creep effects; the structural heritage and culture of the United Arab Emirates. The capacity of elements and the long-term response and slender structural stem supports an elongated bud at capacity of the ground. the top of the Tower where the observation decks, el- In the last 20 years, designers of super-tall build- evated garden, hotel and rotating balconies occur. ings in the Middle East have embraced the challenges The slender structure is anchored to the ground and of meeting stringent construction timelines and high stabilised by an array of cable stays suggesting the loads, without being able to properly draw on more delicate ribbing of lily leaves. efficiency within the ground. Iconic projects such as According to the CTBUH, a skyscraper is defined the Emirates Twin Towers (a tall building duo), the as a structure where over 50% of its height is occupi- Burj Khalifa (developed by Emaar Properties) and the able and it is self-supporting. The Dubai Creek Tower Nakheel Tall Tower Projects (both mega-tall sky- is thus an observation tower and sets itself apart from scrapers), started challenging conventional design the other tall buildings in Dubai by its extremely high and parameter selection using sophisticated labora- slenderness and it being cable-stayed. This creates a tory and full-scale testing (Poulos and Bunce, 2008; new challenge for the foundation design of this mega- Poulos, 2009 and Haberfield et al, 2008). tall structure. The design of the Dubai Creek Tower has once again pushed this envelope of thinking. To ensure that 4 A TOTAL ENGINEERING GEOLOGICAL the design met the challenges of stringent construc- APPROACH AND A “LIVE” MODEL tion schedules and efficient parameter selection, re- quired building on the legacies and knowledge of pre- Poulos (2009) gives a detailed summary of Du- vious mega-tall buildings and applying this in a new bai’s geological and geotechnical conditions, includ- creative way that ensures ultimate value for the client, ing work by Evans (1978) and Kent (1978) and recent satisfying the schedule need and economical cost. projects such as Emirate Twin Towers, Burj Khalifa This is the nature of science and innovation. and Nakheel Tall Tower. The geology of Dubai was primarily formed by the deposition of marine sedi- 3 THE DUBAI CREEK TOWER ments associated with a number of sea level changes during the Quaternary and Pleistocene periods. The The Dubai Creek Tower is a mega-tall building de- ‘young’ sedimentary rocks are classified as sand- signed by world-renowned architect and engineer stone, calcarenite and calcisiltite being commonly Santiago Calatrava. An architectural rendering of the found. Tower structure is illustrated in Figure 1. It will be the Typically, the ground conditions comprise a sub- focal point of a new development, the Dubai Creek surface profile which is complex and highly variable Harbour, located at the Creek in Dubai. It is currently in relation to thickness of strata, cementation and oc- under construction and upon completion will comple- currence of gypsum layers. This is due to the nature ment Dubai’s Burj Khalifa in reaching new heights. of deposition, seismic activity, river channels and the hot arid climatic conditions (Russo et al., 2013). For the Dubai Creek Tower project, like many con- struction projects, geotechnics and the foundation de- sign determined the initial critical path. The first pro- cess of innovation arose around the building of a live geotechnical model based on the Total Engineering Geology approach of Fookes et al. (2000). By gather- ing as much information as possible of sites around the proposed Dubai Creek Tower site and further afield, a model was created of possible subsoil condi- tion. This created a design geotechnical model, giv- ing a sense of variability of geology and geotechnical parameters. The Total Engineering Geology approach allowed the model to be updated as new information emerged from the extensive geotechnical investigation (GI) that followed, thereby consistently honing the model and the design. This allowed early sizing and devel- Figure 1. The Dubai Creek Tower (Image courtesy of Emaar oping of foundation concepts to be formulated and Properties) was essential for the design teams to remain ahead of construction, whilst delivering a safe and reliable de- sign. The GI ultimately comprised of 68 No. boreholes pile capacity for barrettes acting in tension throughout of various depths and a range of in situ

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