Optimum design methodologies for pile foundations in London Christos Letsios a , Nikos D. Lagaros b,⇑ , Manolis Papadrakakis b a Engineering & Construction Department, Facilities Maintenance Directorate, Hellenic Aerospace Industry S.A., P.O. Box 23, 320 09 Schimatari, Greece b Institute of Structural Analysis & Antiseismic Research, School of Civil Engineering, National Technical University of Athens, Zografou Campus, Athens 157 80, Greece article info Article history: Available online 8 August 2014 Keywords: Pile foundations Design codes Optimum design abstract Given the importance of pile foundations in geotechnical engineering for supporting high- significance structures such as bridges, high-rise buildings, power plant stations, offshore platforms and museums, it becomes a necessity to find the best pile foundation design in terms of performance and economy. The number of piles required might exceed several hundreds or even thousands while the pile foundation cost might exceed 20% of the con- struction cost of the superstructure. In this work the problem of finding optimized designs of pile foundations is examined and is performed in accordance to two design code recom- mendations, namely Eurocode 7 and DIN 4014. The proposed structural optimization pro- cedure is implemented in two real-world cases both located in London, UK in order to assess the efficiency of the proposed design formulation. Ó 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Introduction Pile-supported structures are known to have existed in pre-historic times, references to cedar timber piles in Babylon can be found in the Bible. In the Middle Ages, pile foundations supported a wide assortment of structures particularly in Venice and in the Netherlands. Piled foundations are a convenient method for supporting structures built over water or where uplift loads must be resisted. Inclined or raking piles have been also used to resist lateral forces. Piles supporting retaining walls, bridge piers and abutments and machinery foundations resist both vertical and horizontal loads. The main types of piles used are driven piles, driven and cast-in-place piles, jacked piles, bored and cast-in-place piles and composite piles [1]. The first three of the above types are also called displacement piles since the soil is displaced as the pile is driven or jacked into the ground. In the case of bored piles, and in some forms of composite piles, the soil is first removed by boring a hole where concrete is placed or various types of precast concrete or other proprietary units are inserted. Following the decision that piling is necessary, the engineer must make a choice from variety of types and sizes. Usually, there is only one type of pile which is satisfactory for a particular site condition [2]. In this work bearing piles will be exam- ined although any type of piles may also be considered in the proposed formulation. Bearing piles are required when the soil at normal foundation level cannot support ordinary pad, strip, or raft foundations or where structures are sited on deep fill- ing which is compressible and settling under its own weight. The foundation cost, of real-world structural systems, can vary from 5% to 20% of the construction cost of the superstruc- ture while the number of piles required might exceed several hundreds or even thousands. In the first part of this study the modelling of the soil-pile structure interaction using the finite element method is described while in the second part a formulation of an optimization problem is proposed, aiming at achieving the most economical-optimized design of the pile http://dx.doi.org/10.1016/j.csse.2014.08.001 2214-3998/Ó 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). ⇑ Corresponding author. E-mail addresses: xletsios@yahoo.gr (C. Letsios), nlagaros@central.ntua.gr (N.D. Lagaros), mpapadra@central.ntua.gr (M. Papadrakakis). Case Studies in Structural Engineering 2 (2014) 24–32 Contents lists available at ScienceDirect Case Studies in Structural Engineering journal homepage: www.elsevier.com/locate/csse